Darwin and Modern Science
A.C. Seward

Part 3 out of 14

strains without further selection, has, until a few years ago, been almost
entirely lost sight of. Only a very few agriculturists have applied it:
among these are Patrick Shirreff ("Die Verbesserung der Getreide-Arten",
translated by R. Hesse, Halle, 1880.) in Scotland and Willet M. Hays
("Wheat, varieties, breeding, cultivation", Univ. Minnesota, Agricultural
Experimental Station, Bull. no. 62, 1899.) in Minnesota. Patrick Shirreff
observed the fact, that in large fields of cereals, single plants may from
time to time be found with larger ears, which justify the expectation of a
far greater yield. In the course of about twenty-five years he isolated in
this way two varieties of wheat and two of oats. He simply multiplied them
as fast as possible, without any selection, and put them on the market.

Hays was struck by the fact that the yield of wheat in Minnesota was far
beneath that in the neighbouring States. The local varieties were Fife and
Blue Stem. They gave him, on inspection, some better specimens,
"phenomenal yielders" as he called them. These were simply isolated and
propagated, and, after comparison with the parent-variety and with some
other selected strains of less value, were judged to be of sufficient
importance to be tested by cultivation all over the State of Minnesota.
They have since almost supplanted the original types, at least in most
parts of the State, with the result that the total yield of wheat in
Minnesota is said to have been increased by about a million dollars yearly.

Definite progress in the method of single-ear sowing has, however, been
made only recently. It had been foreshadowed by Patrick Shirreff, who
after the production of the four varieties already mentioned, tried to
carry out his work on a larger scale, by including numerous minor
deviations from the main type. He found by doing so that the chances of
obtaining a better form were sufficiently increased to justify the trial.
But it was Nilsson who discovered the almost inexhaustible polymorphy of
cereals and other agricultural crops and made it the starting-point for a
new and entirely trustworthy method of the highest utility. By this means
he has produced during the last fifteen years a number of new and valuable
races, which have already supplanted the old types on numerous farms in
Sweden and which are now being introduced on a large scale into Germany and
other European countries.

It is now twenty years since the station at Svalof was founded. During the
first period of its work, embracing about five years, selection was
practised on the principle which was then generally used in Germany. In
order to improve a race a sample of the best ears was carefully selected
from the best fields of the variety. These ears were considered as
representatives of the type under cultivation, and it was assumed that by
sowing their grains on a small plot a family could be obtained, which could
afterwards be improved by a continuous selection. Differences between the
collected ears were either not observed or disregarded. At Svalof this
method of selection was practised on a far larger scale than on any German
farm, and the result was, broadly speaking, the same. This may be stated
in the following words: improvement in a few cases, failure in all the
others. Some few varieties could be improved and yielded excellent new
types, some of which have since been introduced into Swedish agriculture
and are now prominent races in the southern and middle parts of the
country. But the station had definite aims, and among them was the
improvement of the Chevalier barley. This, in Middle Sweden, is a fine
brewer's barley, but liable to failure during unfavourable summers on
account of its slender stems. It was selected with a view of giving it
stiffer stems, but in spite of all the care and work bestowed upon it no
satisfactory result was obtained.

This experience, combined with a number of analogous failures, could not
fail to throw doubt upon the whole method. It was evident that good
results were only exceptions, and that in most cases the principle was not
one that could be relied upon. The exceptions might be due to unknown
causes, and not to the validity of the method; it became therefore of much
more interest to search for the causes than to continue the work along
these lines.

In the year 1892 a number of different varieties of cereals were cultivated
on a large scale and a selection was again made from them. About two
hundred samples of ears were chosen, each apparently constituting a
different type. Their seeds were sown on separate plots and manured and
treated as much as possible in the same manner. The plots were small and
arranged in rows so as to facilitate the comparison of allied types.
During the whole period of growth and during the ripening of the ears the
plots were carefully studied and compared: they were harvested separately;
ears and kernels were counted and weighed, and notes were made concerning
layering, rust and other cereal pests.

The result of this experiment was, in the main, no distinct improvement.
Nilsson was especially struck by the fact that the plots, which should
represent distinct types, were far from uniform. Many of them were as
multiform as the fields from which the parent-ears were taken. Others
showed variability in a less degree, but in almost all of them it was clear
that a pure race had not been obtained. The experiment was a fair one,
inasmuch as it demonstrated the polymorphic variability of cereals beyond
all doubt and in a degree hitherto unsuspected; but from the standpoint of
the selectionist it was a failure. Fortunately there were, however, one or
two exceptions. A few lots showed a perfect uniformity in regard to all
the stalks and ears: these were small families. This fact suggested the
idea that each might have been derived from a single ear. During the
selection in the previous summer, Nilsson had tried to find as many ears as
possible of each new type which he recognised in his fields. But the
variability of his crops was so great, that he was rarely able to include
more than two or three ears in the same group, and, in a few cases, he
found only one representative of the supposed type. It might, therefore,
be possible that those small uniform plots were the direct progeny of ears,
the grains of which had not been mixed with those from other ears before
sowing. Exact records had, of course, been kept of the chosen samples, and
the number of ears had been noted in each case. It was, therefore,
possible to answer the question and it was found that those plots alone
were uniform on which the kernels of one single ear only had been sown.
Nilsson concluded that the mixture of two or more ears in a single sowing
might be the cause of the lack of uniformity in the progeny. Apparently
similar ears might be different in their progeny.

Once discovered, this fact was elevated to the rank of a leading principle
and tested on as large a scale as possible. The fields were again
carefully investigated and every single ear, which showed a distinct
divergence from the main type in one character or another, was selected. A
thousand samples were chosen, but this time each sample consisted of one
ear only. Next year, the result corresponded to the expectation.
Uniformity prevailed almost everywhere; only a few lots showed a
discrepancy, which might be ascribed to the accidental selection of hybrid
ears. It was now clear that the progeny of single ears was, as a rule,
pure, whereas that of mixed ears was impure. The single-ear selection or
single-ear sowing, which had fallen into discredit in Germany and elsewhere
in Europe, was rediscovered. It proved to be the only trustworthy
principle of selection. Once isolated, such single-parent races are
constant from seed and remain true to their type. No further selection is
needed; they have simply to be multiplied and their real value tested.

Patrick Shirreff, in his early experiments, Le Couteur, Hays and others had
observed the rare occurrence of exceptionally good yielders and the value
of their isolation to the agriculturist. The possibility of error in the
choice of such striking specimens and the necessity of judging their value
by their progeny were also known to these investigators, but they had not
the slightest idea of all the possibilities suggested by their principle.
Nilsson, who is a botanist as well as an agriculturist, discovered that,
besides these exceptionably good yielders, every variety of a cereal
consists of hundreds of different types, which find the best conditions for
success when grown together, but which, after isolation, prove to be
constant. Their preference for mixed growth is so definite, that once
isolated, their claims on manure and treatment are found to be much higher
than those of the original mixed variety. Moreover, the greatest care is
necessary to enable them to retain their purity, and as soon as they are
left to themselves they begin to deteriorate through accidental crosses and
admixtures and rapidly return to the mixed condition.

Reverting now to Darwin's discussion of the variability of cereals, we may
conclude that subsequent investigation has proved it to be exactly of the
kind which he describes. The only difference is that in reality it reaches
a degree, quite unexpected by Darwin and his contemporaries. But it is
polymorphic variability in the strictest sense of the word. How the single
constituents of a variety originate we do not see. We may assume, and
there can hardly be a doubt about the truth of the assumption, that a new
character, once produced, will slowly but surely be combined through
accidental crosses with a large number of previously existing types, and so
will tend to double the number of the constituents of the variety. But
whether it first appears suddenly or whether it is only slowly evolved we
cannot determine. It would, of course, be impossible to observe either
process in such a mixture. Only cultures of pure races, of single-parent
races as we have called them, can afford an opportunity for this kind of
observation. In the fields of Svalof new and unexpected qualities have
recently been seen, from time to time, to appear suddenly. These
characters are as distinct as the older ones and appear to be constant from
the moment of their origin.

Darwin has repeatedly insisted that man does not cause variability. He
simply selects the variations given to him by the hand of nature. He may
repeat this process in order to accumulate different new characters in the
same family, thus producing varieties of a higher order. This process of
accumulation would, if continued for a longer time, lead to the
augmentation of the slight differences characteristic of varieties into the
greater differences characteristic of species and genera. It is in this
way that horticultural and agricultural experience contribute to the
problem of the conversion of varieties into species, and to the explanation
of the admirable adaptations of each organism to its complex conditions of
life. In the long run new forms, distinguished from their allies by quite
a number of new characters, would, by the extermination of the older
intermediates, become distinct species.

Thus we see that the theory of the origin of species by means of natural
selection is quite independent of the question, how the variations to be
selected arise. They may arise slowly, from simple fluctuations, or
suddenly, by mutations; in both cases natural selection will take hold of
them, will multiply them if they are beneficial, and in the course of time
accumulate them, so as to produce that great diversity of organic life,
which we so highly admire.

Darwin has left the decision of this difficult and obviously subordinate
point to his followers. But in his Pangenesis hypothesis he has given us
the clue for a close study and ultimate elucidation of the subject under



Professor of Biology in the University of Cambridge.

Darwin's work has the property of greatness in that it may be admired from
more aspects than one. For some the perception of the principle of Natural
Selection stands out as his most wonderful achievement to which all the
rest is subordinate. Others, among whom I would range myself, look up to
him rather as the first who plainly distinguished, collected, and
comprehensively studied that new class of evidence from which hereafter a
true understanding of the process of Evolution may be developed. We each
prefer our own standpoint of admiration; but I think that it will be in
their wider aspect that his labours will most command the veneration of

A treatise written to advance knowledge may be read in two moods. The
reader may keep his mind passive, willing merely to receive the impress of
the writer's thought; or he may read with his attention strained and alert,
asking at every instant how the new knowledge can be used in a further
advance, watching continually for fresh footholds by which to climb higher
still. Of Shelley it has been said that he was a poet for poets: so
Darwin was a naturalist for naturalists. It is when his writings are used
in the critical and more exacting spirit with which we test the outfit for
our own enterprise that we learn their full value and strength. Whether we
glance back and compare his performance with the efforts of his
predecessors, or look forward along the course which modern research is
disclosing, we shall honour most in him not the rounded merit of finite
accomplishment, but the creative power by which he inaugurated a line of
discovery endless in variety and extension. Let us attempt thus to see his
work in true perspective between the past from which it grew, and the
present which is its consequence. Darwin attacked the problem of Evolution
by reference to facts of three classes: Variation; Heredity; Natural
Selection. His work was not as the laity suppose, a sudden and unheralded
revelation, but the first fruit of a long and hitherto barren controversy.
The occurrence of variation from type, and the hereditary transmission of
such variation had of course been long familiar to practical men, and
inferences as to the possible bearing of those phenomena on the nature of
specific difference had been from time to time drawn by naturalists.
Maupertuis, for example, wrote "Ce qui nous reste a examiner, c'est comment
d'un seul individu, il a pu naitre tant d'especes si differentes." And
again "La Nature contient le fonds de toutes ces varietes: mais le hasard
ou l'art les mettent en oeuvre. C'est ainsi que ceux dont l'industrie
s'applique a satisfaire le gout des curieux, sont, pour ainsi dire,
creatures d'especes nouvelles." ("Venus Physique, contenant deux
Dissertations, l'une sur l'origine des Hommes et des Animaux: Et l'autre
sur l'origine des Noirs" La Haye, 1746, pages 124 and 129. For an
introduction to the writings of Maupertuis I am indebted to an article by
Professor Lovejoy in "Popular Sci. Monthly", 1902.)

Such passages, of which many (though few so emphatic) can be found in
eighteenth century writers, indicate a true perception of the mode of
Evolution. The speculations hinted at by Buffon (For the fullest account
of the views of these pioneers of Evolution, see the works of Samuel
Butler, especially "Evolution, Old and New" (2nd edition) 1882. Butler's
claims on behalf of Buffon have met with some acceptance; but after reading
what Butler has said, and a considerable part of Buffon's own works, the
word "hinted" seems to me a sufficiently correct description of the part he
played. It is interesting to note that in the chapter on the Ass, which
contains some of his evolutionary passages, there is a reference to
"plusieurs idees tres-elevees sur la generation" contained in the Letters
of Maupertuis.), developed by Erasmus Darwin, and independently proclaimed
above all by Lamarck, gave to the doctrine of descent a wide renown. The
uniformitarian teaching which Lyell deduced from geological observation had
gained acceptance. The facts of geographical distribution (See especially
W. Lawrence, "Lectures on Physiology", London, 1823, pages 213 f.) had been
shown to be obviously inconsistent with the Mosaic legend. Prichard, and
Lawrence, following the example of Blumenbach, had successfully
demonstrated that the races of Man could be regarded as different forms of
one species, contrary to the opinion up till then received. These
treatises all begin, it is true, with a profound obeisance to the sons of
Noah, but that performed, they continue on strictly modern lines. The
question of the mutability of species was thus prominently raised.

Those who rate Lamarck no higher than did Huxley in his contemptuous phrase
"buccinator tantum," will scarcely deny that the sound of the trumpet had
carried far, or that its note was clear. If then there were few who had
already turned to evolution with positive conviction, all scientific men
must at least have known that such views had been promulgated; and many
must, as Huxley says, have taken up his own position of "critical
expectancy." (See the chapter contributed to the "Life and Letters of
Charles Darwin" II. page 195. I do not clearly understand the sense in
which Darwin wrote (Autobiography, ibid. I. page 87): "It has sometimes
been said that the success of the "Origin" proved 'that the subject was in
the air,' or 'that men's minds were prepared for it.' I do not think that
this is strictly true, for I occasionally sounded not a few naturalists,
and never happened to come across a single one who seemed to doubt about
the permanence of species." This experience may perhaps have been an
accident due to Darwin's isolation. The literature of the period abounds
with indications of "critical expectancy." A most interesting expression
of that feeling is given in the charming account of the "Early Days of
Darwinism" by Alfred Newton, "Macmillan's Magazine", LVII. 1888, page 241.
He tells how in 1858 when spending a dreary summer in Iceland, he and his
friend, the ornithologist John Wolley, in default of active occupation,
spent their days in discussion. "Both of us taking a keen interest in
Natural History, it was but reasonable that a question, which in those days
was always coming up wherever two or more naturalists were gathered
together, should be continually recurring. That question was, 'What is a
species?' and connected therewith was the other question, 'How did a
species begin?'...Now we were of course fairly well acquainted with what
had been published on these subjects." He then enumerates some of these
publications, mentioning among others T. Vernon Wollaston's "Variation of
Species"--a work which has in my opinion never been adequately appreciated.
He proceeds: "Of course we never arrived at anything like a solution of
these problems, general or special, but we felt very strongly that a
solution ought to be found, and that quickly, if the study of Botany and
Zoology was to make any great advance." He then describes how on his
return home he received the famous number of the "Linnean Journal" on a
certain evening. "I sat up late that night to read it; and never shall I
forget the impression it made upon me. Herein was contained a perfectly
simple solution of all the difficulties which had been troubling me for
months past...I went to bed satisfied that a solution had been found.")

Why, then, was it, that Darwin succeeded where the rest had failed? The
cause of that success was two-fold. First, and obviously, in the principle
of Natural Selection he had a suggestion which would work. It might not go
the whole way, but it was true as far as it went. Evolution could thus in
great measure be fairly represented as a consequence of demonstrable
processes. Darwin seldom endangers the mechanism he devised by putting on
it strains much greater than it can bear. He at least was under no
illusion as to the omnipotence of Selection; and he introduces none of the
forced pleading which in recent years has threatened to discredit that

For example, in the latest text of the "Origin" ("Origin", (6th edition
(1882), page 421.) we find him saying:

"But as my conclusions have lately been much misrepresented, and it has
been stated that I attribute the modification of species exclusively to
natural selection, I may be permitted to remark that in the first edition
of this work, and subsequently, I placed in a most conspicuous position--
namely, at the close of the Introduction--the following words: 'I am
convinced that natural selection has been the main but not the exclusive
means of modification.'"

But apart from the invention of this reasonable hypothesis, which may well,
as Huxley estimated, "be the guide of biological and psychological
speculation for the next three or four generations," Darwin made a more
significant and imperishable contribution. Not for a few generations, but
through all ages he should be remembered as the first who showed clearly
that the problems of Heredity and Variation are soluble by observation, and
laid down the course by which we must proceed to their solution. (Whatever
be our estimate of the importance of Natural Selection, in this we all
agree. Samuel Butler, the most brilliant, and by far the most interesting
of Darwin's opponents--whose works are at length emerging from oblivion--in
his Preface (1882) to the 2nd edition of "Evolution, Old and New", repeats
his earlier expression of homage to one whom he had come to regard as an
enemy: "To the end of time, if the question be asked, 'Who taught people
to believe in Evolution?' the answer must be that it was Mr. Darwin. This
is true, and it is hard to see what palm of higher praise can be awarded to
any philosopher.") The moment of inspiration did not come with the reading
of Malthus, but with the opening of the "first note-book on Transmutation
of Species." ("Life and Letters", I. pages 276 and 83.) Evolution is a
process of Variation and Heredity. The older writers, though they had some
vague idea that it must be so, did not study Variation and Heredity.
Darwin did, and so begat not a theory, but a science.

The extent to which this is true, the scientific world is only beginning to
realise. So little was the fact appreciated in Darwin's own time that the
success of his writings was followed by an almost total cessation of work
in that special field. Of the causes which led to this remarkable
consequence I have spoken elsewhere. They proceeded from circumstances
peculiar to the time; but whatever the causes there is no doubt that this
statement of the result is historically exact, and those who make it their
business to collect facts elucidating the physiology of Heredity and
Variation are well aware that they will find little to reward their quest
in the leading scientific Journals of the Darwinian epoch.

In those thirty years the original stock of evidence current and in
circulation even underwent a process of attrition. As in the story of the
Eastern sage who first wrote the collected learning of the universe for his
sons in a thousand volumes, and by successive compression and burning
reduced them to one, and from this by further burning distilled the single
ejaculation of the Faith, "There is no god but God and Mohamed is the
Prophet of God," which was all his maturer wisdom deemed essential:--so in
the books of that period do we find the corpus of genetic knowledge dwindle
to a few prerogative instances, and these at last to the brief formula of
an unquestioned creed.

And yet in all else that concerns biological science this period was, in
very truth, our Golden Age, when the natural history of the earth was
explored as never before; morphology and embryology were exhaustively
ransacked; the physiology of plants and animals began to rival chemistry
and physics in precision of method and in the rapidity of its advances; and
the foundations of pathology were laid.

In contrast with this immense activity elsewhere the neglect which befel
the special physiology of Descent, or Genetics as we now call it, is
astonishing. This may of course be interpreted as meaning that the
favoured studies seemed to promise a quicker return for effort, but it
would be more true to say that those who chose these other pursuits did so
without making any such comparison; for the idea that the physiology of
Heredity and Variation was a coherent science, offering possibilities of
extraordinary discovery, was not present to their minds at all. In a word,
the existence of such a science was well nigh forgotten. It is true that
in ancillary periodicals, as for example those that treat of entomology or
horticulture, or in the writings of the already isolated systematists (This
isolation of the systematists is the one most melancholy sequela of
Darwinism. It seems an irony that we should read in the peroration to the
"Origin" that when the Darwinian view is accepted "Systematists will be
able to pursue their labours as at present; but they will not be
incessantly haunted by the shadowy doubt whether this or that form be a
true species. This, I feel sure, and I speak after experience, will be no
slight relief. The endless disputes whether or not some fifty species of
British brambles are good species will cease." "Origin", 6th edition
(1882), page 425. True they have ceased to attract the attention of those
who lead opinion, but anyone who will turn to the literature of systematics
will find that they have not ceased in any other sense. Should there not
be something disquieting in the fact that among the workers who come most
into contact with specific differences, are to be found the only men who
have failed to be persuaded of the unreality of those differences?),
observations with this special bearing were from time to time related, but
the class of fact on which Darwin built his conceptions of Heredity and
Variation was not seen in the highways of biology. It formed no part of
the official curriculum of biological students, and found no place among
the subjects which their teachers were investigating.

During this period nevertheless one distinct advance was made, that with
which Weismann's name is prominently connected. In Darwin's genetic scheme
the hereditary transmission of parental experience and its consequences
played a considerable role. Exactly how great that role was supposed to
be, he with his habitual caution refrained from specifying, for the
sufficient reason that he did not know. Nevertheless much of the process
of Evolution, especially that by which organs have become degenerate and
rudimentary, was certainly attributed by Darwin to such inheritance, though
since belief in the inheritance of acquired characters fell into disrepute,
the fact has been a good deal overlooked. The "Origin" without "use and
disuse" would be a materially different book. A certain vacillation is
discernible in Darwin's utterances on this question, and the fact gave to
the astute Butler an opportunity for his most telling attack. The
discussion which best illustrates the genetic views of the period arose in
regard to the production of the rudimentary condition of the wings of many
beetles in the Madeira group of islands, and by comparing passages from the
"Origin" (6th edition pages 109 and 401. See Butler, "Essays on Life, Art,
and Science", page 265, reprinted 1908, and "Evolution, Old and New",
chapter XXII. (2nd edition), 1882.) Butler convicts Darwin of saying first
that this condition was in the main the result of Selection, with disuse
aiding, and in another place that the main cause of degeneration was
disuse, but that Selection had aided. To Darwin however I think the point
would have seemed one of dialectics merely. To him the one paramount
purpose was to show that somehow an Evolution by means of Variation and
Heredity might have brought about the facts observed, and whether they had
come to pass in the one way or the other was a matter of subordinate

To us moderns the question at issue has a diminished significance. For
over all such debates a change has been brought by Weismann's challenge for
evidence that use and disuse have any transmitted effects at all. Hitherto
the transmission of many acquired characteristics had seemed to most
naturalists so obvious as not to call for demonstration. (W. Lawrence was
one of the few who consistently maintained the contrary opinion. Prichard,
who previously had expressed himself in the same sense, does not, I believe
repeat these views in his later writings, and there are signs that he came
to believe in the transmission of acquired habits. See Lawrence, "Lect.
Physiol." 1823, pages 436-437, 447 Prichard, Edin. Inaug. Disp. 1808 (not
seen by me), quoted ibid. and "Nat. Hist. Man", 1843, pages 34 f.)
Weismann's demand for facts in support of the main proposition revealed at
once that none having real cogency could be produced. The time-honoured
examples were easily shown to be capable of different explanations. A few
certainly remain which cannot be so summarily dismissed, but--though it is
manifestly impossible here to do justice to such a subject--I think no one
will dispute that these residual and doubtful phenomena, whatever be their
true nature, are not of a kind to help us much in the interpretation of any
of those complex cases of adaptation which on the hypothesis of unguided
Natural Selection are especially difficult to understand. Use and disuse
were invoked expressly to help us over these hard places; but whatever
changes can be induced in offspring by direct treatment of the parents,
they are not of a kind to encourage hope of real assistance from that
quarter. It is not to be denied that through the collapse of this second
line of argument the Selection hypothesis has had to take an increased and
perilous burden. Various ways of meeting the difficulty have been
proposed, but these mostly resolve themselves into improbable attempts to
expand or magnify the powers of Natural Selection.

Weismann's interpellation, though negative in purpose, has had a lasting
and beneficial effect, for through his thorough demolition of the old loose
and distracting notions of inherited experience, the ground has been
cleared for the construction of a true knowledge of heredity based on
experimental fact.

In another way he made a contribution of a more positive character, for his
elaborate speculations as to the genetic meaning of cytological appearances
have led to a minute investigation of the visible phenomena occurring in
those divisions by which germ-cells arise. Though the particular views he
advocated have very largely proved incompatible with the observed facts of
heredity, yet we must acknowledge that it was chiefly through the stimulus
of Weismann's ideas that those advances in cytology were made; and though
the doctrine of the continuity of germ-plasm cannot be maintained in the
form originally propounded, it is in the main true and illuminating. (It
is interesting to see how nearly Butler was led by natural penetration, and
from absolutely opposite conclusions, back to this underlying truth: "So
that each ovum when impregnate should be considered not as descended from
its ancestors, but as being a continuation of the personality of every ovum
in the chain of its ancestry, which every ovum IT ACTUALLY IS quite as
truly as the octogenarian IS the same identity with the ovum from which he
has been developed. This process cannot stop short of the primordial cell,
which again will probably turn out to be but a brief resting-place. We
therefore prove each one of us to BE ACTUALLY the primordial cell which
never died nor dies, but has differentiated itself into the life of the
world, all living beings whatever, being one with it and members one of
another," "Life and Habit", 1878, page 86.) Nevertheless in the present
state of knowledge we are still as a rule quite unable to connect
cytological appearances with any genetic consequence and save in one
respect (obviously of extreme importance--to be spoken of later) the two
sets of phenomena might, for all we can see, be entirely distinct.

I cannot avoid attaching importance to this want of connection between the
nuclear phenomena and the features of bodily organisation. All attempts to
investigate Heredity by cytological means lie under the disadvantage that
it is the nuclear changes which can alone be effectively observed.
Important as they must surely be, I have never been persuaded that the rest
of the cell counts for nothing. What we know of the behaviour and
variability of chromosomes seems in my opinion quite incompatible with the
belief that they alone govern form, and are the sole agents responsible in
heredity. (This view is no doubt contrary to the received opinion. I am
however interested to see it lately maintained by Driesch ("Science and
Philosophy of the Organism", London, 1907, page 233), and from the recent
observations of Godlewski it has received distinct experimental support.)

If, then, progress was to be made in Genetics, work of a different kind was
required. To learn the laws of Heredity and Variation there is no other
way than that which Darwin himself followed, the direct examination of the
phenomena. A beginning could be made by collecting fortuitous observations
of this class, which have often thrown a suggestive light, but such
evidence can be at best but superficial and some more penetrating
instrument of research is required. This can only be provided by actual
experiments in breeding.

The truth of these general considerations was becoming gradually clear to
many of us when in 1900 Mendel's work was rediscovered. Segregation, a
phenomenon of the utmost novelty, was thus revealed. From that moment not
only in the problem of the origin of species, but in all the great problems
of biology a new era began. So unexpected was the discovery that many
naturalists were convinced it was untrue, and at once proclaimed Mendel's
conclusions as either altogether mistaken, or if true, of very limited
application. Many fantastic notions about the workings of Heredity had
been asserted as general principles before: this was probably only another
fancy of the same class.

Nevertheless those who had a preliminary acquaintance with the facts of
Variation were not wholly unprepared for some such revelation. The
essential deduction from the discovery of segregation was that the
characters of living things are dependent on the presence of definite
elements or factors, which are treated as units in the processes of
Heredity. These factors can thus be recombined in various ways. They act
sometimes separately, and sometimes they interact in conjunction with each
other, producing their various effects. All this indicates a definiteness
and specific order in heredity, and therefore in variation. This order
cannot by the nature of the case be dependent on Natural Selection for its
existence, but must be a consequence of the fundamental chemical and
physical nature of living things. The study of Variation had from the
first shown that an orderliness of this kind was present. The bodies and
the properties of living things are cosmic, not chaotic. No matter how low
in the scale we go, never do we find the slightest hint of a diminution in
that all-pervading orderliness, nor can we conceive an organism existing
for a moment in any other state. Moreover not only does this order prevail
in normal forms, but again and again it is to be seen in newly-sprung
varieties, which by general consent cannot have been subjected to a
prolonged Selection. The discovery of Mendelian elements admirably
coincided with and at once gave a rationale of these facts. Genetic
Variation is then primarily the consequence of additions to, or omissions
from, the stock of elements which the species contains. The further
investigation of the species-problem must thus proceed by the analytical
method which breeding experiments provide.

In the nine years which have elapsed since Mendel's clue became generally
known, progress has been rapid. We now understand the process by which a
polymorphic race maintains its polymorphism. When a family consists of
dissimilar members, given the numerical proportions in which these members
are occurring, we can represent their composition symbolically and state
what types can be transmitted by the various members. The difficulty of
the "swamping effects of intercrossing" is practically at an end. Even the
famous puzzle of sex-limited inheritance is solved, at all events in its
more regular manifestations, and we know now how it is brought about that
the normal sisters of a colour-blind man can transmit the colour-blindness
while his normal brothers cannot transmit it.

We are still only on the fringe of the inquiry. It can be seen extending
and ramifying in many directions. To enumerate these here would be
impossible. A whole new range of possibilities is being brought into view
by study of the interrelations between the simple factors. By following up
the evidence as to segregation, indications have been obtained which can
only be interpreted as meaning that when many factors are being
simultaneously redistributed among the germ-cells, certain of them exert
what must be described as a repulsion upon other factors. We cannot
surmise whither this discovery may lead.

In the new light all the old problems wear a fresh aspect. Upon the
question of the nature of Sex, for example, the bearing of Mendelian
evidence is close. Elsewhere I have shown that from several sets of
parallel experiments the conclusion is almost forced upon us that, in the
types investigated, of the two sexes the female is to be regarded as
heterozygous in sex, containing one unpaired dominant element, while the
male is similarly homozygous in the absence of that element. (In other
words, the ova are each EITHER female, OR male (i.e. non-female), but the
sperms are all non-female.) It is not a little remarkable that on this
point--which is the only one where observations of the nuclear processes of
gameto-genesis have yet been brought into relation with the visible
characteristics of the organisms themselves--there should be diametrical
opposition between the results of breeding experiments and those derived
from cytology.

Those who have followed the researches of the American school will be aware
that, after it had been found in certain insects that the spermatozoa were
of two kinds according as they contained or did not contain the accessory
chromosome, E.B. Wilson succeeded in proving that the sperms possessing
this accessory body were destined to form FEMALES on fertilisation, while
sperms without it form males, the eggs being apparently indifferent.
Perhaps the most striking of all this series of observations is that lately
made by T.H. Morgan (Morgan, "Proc. Soc. Exp. Biol. Med." V. 1908, and von
Baehr, "Zool. Anz." XXXII. page 507, 1908.), since confirmed by von Baehr,
that in a Phylloxeran two kinds of spermatids are formed, respectively with
and without an accessory (in this case, DOUBLE) chromosome. Of these, only
those possessing the accessory body become functional spermatozoa, the
others degenerating. We have thus an elucidation of the puzzling fact that
in these forms fertilisation results in the formation of FEMALES only. How
the males are formed--for of course males are eventually produced by the
parthenogenetic females--we do not know.

If the accessory body is really to be regarded as bearing the factor for
femaleness, then in Mendelian terms female is DD and male is DR. The eggs
are indifferent and the spermatozoa are each male, OR female. But
according to the evidence derived from a study of the sex-limited descent
of certain features in other animals the conclusion seems equally clear
that in them female must be regarded as DR and male as RR. The eggs are
thus each either male or female and the spermatozoa are indifferent. How
this contradictory evidence is to be reconciled we do not yet know. The
breeding work concerns fowls, canaries, and the Currant moth (Abraxas
grossulariata). The accessory chromosome has been now observed in most of
the great divisions of insects (As Wilson has proved, the unpaired body is
not a universal feature even in those orders in which it has been observed.
Nearly allied types may differ. In some it is altogether unpaired. In
others it is paired with a body of much smaller size, and by selection of
various types all gradations can be demonstrated ranging to the condition
in which the members of the pair are indistinguishable from each other.),
except, as it happens, Lepidoptera. At first sight it seems difficult to
suppose that a feature apparently so fundamental as sex should be
differently constituted in different animals, but that seems at present the
least improbable inference. I mention these two groups of facts as
illustrating the nature and methods of modern genetic work. We must
proceed by minute and specific analytical investigation. Wherever we look
we find traces of the operation of precise and specific rules.

In the light of present knowledge it is evident that before we can attack
the Species-problem with any hope of success there are vast arrears to be
made up. He would be a bold man who would now assert that there was no
sense in which the term Species might not have a strict and concrete
meaning in contradistinction to the term Variety. We have been taught to
regard the difference between species and variety as one of degree. I
think it unlikely that this conclusion will bear the test of further
research. To Darwin the question, What is a variation? presented no
difficulties. Any difference between parent and offspring was a variation.
Now we have to be more precise. First we must, as de Vries has shown,
distinguish real, genetic, variation from FLUCTUATIONAL variations, due to
environmental and other accidents, which cannot be transmitted. Having
excluded these sources of error the variations observed must be expressed
in terms of the factors to which they are due before their significance can
be understood. For example, numbers of the variations seen under
domestication, and not a few witnessed in nature, are simply the
consequence of some ingredient being in an unknown way omitted from the
composition of the varying individual. The variation may on the contrary
be due to the addition of some new element, but to prove that it is so is
by no means an easy matter. Casual observation is useless, for though
these latter variations will always be dominants, yet many dominant
characteristics may arise from another cause, namely the meeting of
complementary factors, and special study of each case in two generations at
least is needed before these two phenomena can be distinguished.

When such considerations are fully appreciated it will be realised that
medleys of most dissimilar occurrences are all confused together under the
term Variation. One of the first objects of genetic analysis is to
disentangle this mass of confusion.

To those who have made no study of heredity it sometimes appears that the
question of the effect of conditions in causing variation is one which we
should immediately investigate, but a little thought will show that before
any critical inquiry into such possibilities can be attempted, a knowledge
of the working of heredity under conditions as far as possible uniform must
be obtained. At the time when Darwin was writing, if a plant brought into
cultivation gave off an albino variety, such an event was without
hesitation ascribed to the change of life. Now we see that albino GAMETES,
germs, that is to say, which are destitute of the pigment-forming factor,
may have been originally produced by individuals standing an indefinite
number of generations back in the ancestry of the actual albino, and it is
indeed almost certain that the variation to which the appearance of the
albino is due cannot have taken place in a generation later than that of
the grandparents. It is true that when a new DOMINANT appears we should
feel greater confidence that we were witnessing the original variation, but
such events are of extreme rarity, and no such case has come under the
notice of an experimenter in modern times, as far as I am aware. That they
must have appeared is clear enough. Nothing corresponding to the Brown-
breasted Game fowl is known wild, yet that colour is a most definite
dominant, and at some moment since Gallus bankiva was domesticated, the
element on which that special colour depends must have at least once been
formed in the germ-cell of a fowl; but we need harder evidence than any
which has yet been produced before we can declare that this novelty came
through over-feeding, or change of climate, or any other disturbance
consequent on domestication. When we reflect on the intricacies of genetic
problems as we must now conceive them there come moments when we feel
almost thankful that the Mendelian principles were unknown to Darwin. The
time called for a bold pronouncement, and he made it, to our lasting profit
and delight. With fuller knowledge we pass once more into a period of
cautious expectation and reserve.

In every arduous enterprise it is pleasanter to look back at difficulties
overcome than forward to those which still seem insurmountable, but in the
next stage there is nothing to be gained by disguising the fact that the
attributes of living things are not what we used to suppose. If they are
more complex in the sense that the properties they display are throughout
so regular (I have in view, for example, the marvellous and specific
phenomena of regeneration, and those discovered by the students of
"Entwicklungsmechanik". The circumstances of its occurrence here preclude
any suggestion that this regularity has been brought about by the workings
of Selection. The attempts thus to represent the phenomena have resulted
in mere parodies of scientific reasoning.) that the Selection of minute
random variations is an unacceptable account of the origin of their
diversity, yet by virtue of that very regularity the problem is limited in
scope and thus simplified.

To begin with, we must relegate Selection to its proper place. Selection
permits the viable to continue and decides that the non-viable shall
perish; just as the temperature of our atmosphere decides that no liquid
carbon shall be found on the face of the earth: but we do not suppose that
the form of the diamond has been gradually achieved by a process of
Selection. So again, as the course of descent branches in the successive
generations, Selection determines along which branch Evolution shall
proceed, but it does not decide what novelties that branch shall bring
forth. "La Nature contient le fonds de toutes ces varietes, mais le hazard
ou l'art les mettent en oeuvre," as Maupertuis most truly said.

Not till knowledge of the genetic properties of organisms has attained to
far greater completeness can evolutionary speculations have more than a
suggestive value. By genetic experiment, cytology and physiological
chemistry aiding, we may hope to acquire such knowledge. In 1872 Nathusius
wrote ("Vortrage uber Viehzucht und Rassenerkenntniss", page 120, Berlin,
1872.): "Das Gesetz der Vererbung ist noch nicht erkannt; der Apfel ist
noch nicht vom Baum der Erkenntniss gefallen, welcher, der Sage nach,
Newton auf den rechten Weg zur Ergrundung der Gravitationsgesetze fuhrte."
We cannot pretend that the words are not still true, but in Mendelian
analysis the seeds of that apple-tree at last are sown.

If we were asked what discovery would do most to forward our inquiry, what
one bit of knowledge would more than any other illuminate the problem, I
think we may give the answer without hesitation. The greatest advance that
we can foresee will be made when it is found possible to connect the
geometrical phenomena of development with the chemical. The geometrical
symmetry of living things is the key to a knowledge of their regularity,
and the forces which cause it. In the symmetry of the dividing cell the
basis of that resemblance we call Heredity is contained. To imitate the
morphological phenomena of life we have to devise a system which can
divide. It must be able to divide, and to segment as--grossly--a vibrating
plate or rod does, or as an icicle can do as it becomes ribbed in a
continuous stream of water; but with this distinction, that the
distribution of chemical differences and properties must simultaneously be
decided and disposed in orderly relation to the pattern of the
segmentation. Even if a model which would do this could be constructed it
might prove to be a useful beginning.

This may be looking too far ahead. If we had to choose some one piece of
more proximate knowledge which we would more especially like to acquire, I
suppose we should ask for the secret of interracial sterility. Nothing has
yet been discovered to remove the grave difficulty, by which Huxley in
particular was so much oppressed, that among the many varieties produced
under domestication--which we all regard as analogous to the species seen
in nature--no clear case of interracial sterility has been demonstrated.
The phenomenon is probably the only one to which the domesticated products
seem to afford no parallel. No solution of the difficulty can be offered
which has positive value, but it is perhaps worth considering the facts in
the light of modern ideas. It should be observed that we are not
discussing incompatibility of two species to produce offspring (a totally
distinct phenomenon), but the sterility of the offspring which many of them
do produce.

When two species, both perfectly fertile severally, produce on crossing a
sterile progeny, there is a presumption that the sterility is due to the
development in the hybrid of some substance which can only be formed by the
meeting of two complementary factors. That some such account is correct in
essence may be inferred from the well-known observation that if the hybrid
is not totally sterile but only partially so, and thus is able to form some
good germ-cells which develop into new individuals, the sterility of these
daughter-individuals is sensibly reduced or may be entirely absent. The
fertility once re-established, the sterility does not return in the later
progeny, a fact strongly suggestive of segregation. Now if the sterility
of the cross-bred be really the consequence of the meeting of two
complementary factors, we see that the phenomenon could only be produced
among the divergent offspring of one species by the acquisition of at least
TWO new factors; for if the acquisition of a single factor caused sterility
the line would then end. Moreover each factor must be separately acquired
by distinct individuals, for if both were present together, the possessors
would by hypothesis be sterile. And in order to imitate the case of
species each of these factors must be acquired by distinct breeds. The
factors need not, and probably would not, produce any other perceptible
effects; they might, like the colour-factors present in white flowers, make
no difference in the form or other characters. Not till the cross was
actually made between the two complementary individuals would either factor
come into play, and the effects even then might be unobserved until an
attempt was made to breed from the cross-bred.

Next, if the factors responsible for sterility were acquired, they would in
all probability be peculiar to certain individuals and would not readily be
distributed to the whole breed. Any member of the breed also into which
BOTH the factors were introduced would drop out of the pedigree by virtue
of its sterility. Hence the evidence that the various domesticated breeds
say of dogs or fowls can when mated together produce fertile offspring, is
beside the mark. The real question is, Do they ever produce sterile
offspring? I think the evidence is clearly that sometimes they do, oftener
perhaps than is commonly supposed. These suggestions are quite amenable to
experimental tests. The most obvious way to begin is to get a pair of
parents which are known to have had any sterile offspring, and to find the
proportions in which these steriles were produced. If, as I anticipate,
these proportions are found to be definite, the rest is simple.

In passing, certain other considerations may be referred to. First, that
there are observations favouring the view that the production of totally
sterile cross-breds is seldom a universal property of two species, and that
it may be a matter of individuals, which is just what on the view here
proposed would be expected. Moreover, as we all know now, though
incompatibility may be dependent to some extent on the degree to which the
species are dissimilar, no such principle can be demonstrated to determine
sterility or fertility in general. For example, though all our Finches can
breed together, the hybrids are all sterile. Of Ducks some species can
breed together without producing the slightest sterility; others have
totally sterile offspring, and so on. The hybrids between several genera
of Orchids are perfectly fertile on the female side, and some on the male
side also, but the hybrids produced between the Turnip (Brassica napus) and
the Swede (Brassica campestris), which, according to our estimates of
affinity should be nearly allied forms, are totally sterile. (See Sutton,
A.W., "Journ. Linn. Soc." XXXVIII. page 341, 1908.) Lastly, it may be
recalled that in sterility we are almost certainly considering a meristic
phenomenon. FAILURE TO DIVIDE is, we may feel fairly sure, the immediate
"cause" of the sterility. Now, though we know very little about the
heredity of meristic differences, all that we do know points to the
conclusion that the less-divided is dominant to the more-divided, and we
are thus justified in supposing that there are factors which can arrest or
prevent cell-division. My conjecture therefore is that in the case of
sterility of cross-breds we see the effect produced by a complementary pair
of such factors. This and many similar problems are now open to our

The question is sometimes asked, Do the new lights on Variation and
Heredity make the process of Evolution easier to understand? On the whole
the answer may be given that they do. There is some appearance of loss of
simplicity, but the gain is real. As was said above, the time is not ripe
for the discussion of the origin of species. With faith in Evolution
unshaken--if indeed the word faith can be used in application to that which
is certain--we look on the manner and causation of adapted differentiation
as still wholly mysterious. As Samuel Butler so truly said: "To me it
seems that the 'Origin of Variation,' whatever it is, is the only true
'Origin of Species'" ("Life and Habit", London, page 263, 1878.), and of
that Origin not one of us knows anything. But given Variation--and it is
given: assuming further that the variations are not guided into paths of
adaptation--and both to the Darwinian and to the modern school this
hypothesis appears to be sound if unproven--an evolution of species
proceeding by definite steps is more, rather than less, easy to imagine
than an evolution proceeding by the accumulation of indefinite and
insensible steps. Those who have lost themselves in contemplating the
miracles of Adaptation (whether real or spurious) have not unnaturally
fixed their hopes rather on the indefinite than on the definite changes.
The reasons are obvious. By suggesting that the steps through which an
adaptative mechanism arose were indefinite and insensible, all further
trouble is spared. While it could be said that species arise by an
insensible and imperceptible process of variation, there was clearly no use
in tiring ourselves by trying to perceive that process. This labour-saving
counsel found great favour. All that had to be done to develop evolution-
theory was to discover the good in everything, a task which, in the
complete absence of any control or test whereby to check the truth of the
discovery, is not very onerous. The doctrine "que tout est au mieux" was
therefore preached with fresh vigour, and examples of that illuminating
principle were discovered with a facility that Pangloss himself might have
envied, till at last even the spectators wearied of such dazzling

But in all seriousness, why should indefinite and unlimited variation have
been regarded as a more probable account of the origin of Adaptation?
Only, I think, because the obstacle was shifted one plane back, and so
looked rather less prominent. The abundance of Adaptation, we all grant,
is an immense, almost an unsurpassable difficulty in all non-Lamarckian
views of Evolution; but if the steps by which that adaptation arose were
fortuitous, to imagine them insensible is assuredly no help. In one most
important respect indeed, as has often been observed, it is a
multiplication of troubles. For the smaller the steps, the less could
Natural Selection act upon them. Definite variations--and of the
occurrence of definite variations in abundance we have now the most
convincing proof--have at least the obvious merit that they can make and
often do make a real difference in the chances of life.

There is another aspect of the Adaptation problem to which I can only
allude very briefly. May not our present ideas of the universality and
precision of Adaptation be greatly exaggerated? The fit of organism to its
environment is not after all so very close--a proposition unwelcome
perhaps, but one which could be illustrated by very copious evidence.
Natural Selection is stern, but she has her tolerant moods.

We have now most certain and irrefragable proof that much definiteness
exists in living things apart from Selection, and also much that may very
well have been preserved and so in a sense constituted by Selection. Here
the matter is likely to rest. There is a passage in the sixth edition of
the "Origin" which has I think been overlooked. On page 70 Darwin says
"The tuft of hair on the breast of the wild turkey-cock cannot be of any
use, and it is doubtful whether it can be ornamental in the eyes of the
female bird." This tuft of hair is a most definite and unusual structure,
and I am afraid that the remark that it "cannot be of any use" may have
been made inadvertently; but it may have been intended, for in the first
edition the usual qualification was given and must therefore have been
deliberately excised. Anyhow I should like to think that Darwin did throw
over that tuft of hair, and that he felt relief when he had done so.
Whether however we have his great authority for such a course or not, I
feel quite sure that we shall be rightly interpreting the facts of nature
if we cease to expect to find purposefulness wherever we meet with definite
structures or patterns. Such things are, as often as not, I suspect rather
of the nature of tool-marks, mere incidents of manufacture, benefiting
their possessor not more than the wire-marks in a sheet of paper, or the
ribbing on the bottom of an oriental plate renders those objects more
attractive in our eyes.

If Variation may be in any way definite, the question once more arises, may
it not be definite in direction? The belief that it is has had many
supporters, from Lamarck onwards, who held that it was guided by need, and
others who, like Nageli, while laying no emphasis on need, yet were
convinced that there was guidance of some kind. The latter view under the
name of "Orthogenesis," devised I believe by Eimer, at the present day
commends itself to some naturalists. The objection to such a suggestion is
of course that no fragment of real evidence can be produced in its support.
On the other hand, with the experimental proof that variation consists
largely in the unpacking and repacking of an original complexity, it is not
so certain as we might like to think that the order of these events is not
pre-determined. For instance the original "pack" may have been made in
such a way that at the nth division of the germ-cells of a Sweet Pea a
colour-factor might be dropped, and that at the n plus n prime division the
hooded variety be given off, and so on. I see no ground whatever for
holding such a view, but in fairness the possibility should not be
forgotten, and in the light of modern research it scarcely looks so
absurdly improbable as before.

No one can survey the work of recent years without perceiving that
evolutionary orthodoxy developed too fast, and that a great deal has got to
come down; but this satisfaction at least remains, that in the experimental
methods which Mendel inaugurated, we have means of reaching certainty in
regard to the physiology of Heredity and Variation upon which a more
lasting structure may be built.


Professor of Botany in the University of Bonn.

Since 1875 an unexpected insight has been gained into the internal
structure of cells. Those who are familiar with the results of
investigations in this branch of Science are convinced that any modern
theory of heredity must rest on a basis of cytology and cannot be at
variance with cytological facts. Many histological discoveries, both such
as have been proved correct and others which may be accepted as probably
well founded, have acquired a fundamental importance from the point of view
of the problems of heredity.

My aim is to describe the present position of our knowledge of Cytology.
The account must be confined to essentials and cannot deal with far-
reaching and controversial questions. In cases where difference of opinion
exists, I adopt my own view for which I hold myself responsible. I hope to
succeed in making myself intelligible even without the aid of
illustrations: in order to convey to the uninitiated an adequate idea of
the phenomena connected with the life of a cell, a greater number of
figures would be required than could be included within the scope of this

So long as the most eminent investigators (As for example the illustrious
Wilhelm Hofmeister in his "Lehre von der Pflanzenzelle" (1867).) believed
that the nucleus of a cell was destroyed in the course of each division and
that the nuclei of the daughter-cells were produced de novo, theories of
heredity were able to dispense with the nucleus. If they sought, as did
Charles Darwin, who showed a correct grasp of the problem in the
enunciation of his Pangenesis hypothesis, for histological connecting
links, their hypotheses, or at least the best of them, had reference to the
cell as a whole. It was known to Darwin that the cell multiplied by
division and was derived from a similar pre-existing cell. Towards 1870 it
was first demonstrated that cell-nuclei do not arise de novo, but are
invariably the result of division of pre-existing nuclei. Better methods
of investigation rendered possible a deeper insight into the phenomena
accompanying cell and nuclear divisions and at the same time disclosed the
existence of remarkable structures. The work of O. Butschli, O. Hertwig,
W. Flemming H. Fol and of the author of this article (For further reference
to literature, see my article on "Die Ontogenie der Zelle seit 1875", in
the "Progressus Rei Botanicae", Vol. I. page 1, Jena, 1907.), have
furnished conclusive evidence in favour of these facts. It was found that
when the reticular framework of a nucleus prepares to divide, it separates
into single segments. These then become thicker and denser, taking up with
avidity certain stains, which are used as aids to investigation, and
finally form longer or shorter, variously bent, rodlets of uniform
thickness. In these organs which, on account of their special property of
absorbing certain stains, were styled Chromosomes (By W. Waldeyer in
1888.), there may usually be recognised a separation into thicker and
thinner discs; the former are often termed Chromomeres. (Discovered by W.
Pfitzner in 1880.) In the course of division of the nucleus, the single
rows of chromomeres in the chromosomes are doubled and this produces a
band-like flattening and leads to the longitudinal splitting by which each
chromosome is divided into two exactly equal halves. The nuclear membrane
then disappears and fibrillar cell-plasma or cytoplasm invades the nuclear
area. In animal cells these fibrillae in the cytoplasm centre on definite
bodies (Their existence and their multiplication by fission were
demonstrated by E. van Beneden and Th. Boveri in 1887.), which it is
customary to speak of as Centrosomes. Radiating lines in the adjacent
cell-plasma suggest that these bodies constitute centres of force. The
cells of the higher plants do not possess such individualised centres; they
have probably disappeared in the course of phylogenetic development: in
spite of this, however, in the nuclear division-figures the fibrillae of
the cell-plasma are seen to radiate from two opposite poles. In both
animal and plant cells a fibrillar bipolar spindle is formed, the fibrillae
of which grasp the longitudinally divided chromosomes from two opposite
sides and arrange them on the equatorial plane of the spindle as the so-
called nuclear or equatorial plate. Each half-chromosome is connected with
one of the spindle poles only and is then drawn towards that pole. (These
important facts, suspected by W. Flemming in 1882, were demonstrated by E.
Heuser, L. Guignard, E. van Beneden, M. Nussbaum, and C. Rabl.)

The formation of the daughter-nuclei is then effected. The changes which
the daughter-chromosomes undergo in the process of producing the daughter-
nuclei repeat in the reverse order the changes which they went through in
the course of their progressive differentiation from the mother-nucleus.
The division of the cell-body is completed midway between the two daughter-
nuclei. In animal cells, which possess no chemically differentiated
membrane, separation is effected by simple constriction, while in the case
of plant cells provided with a definite wall, the process begins with the
formation of a cytoplasmic separating layer.

The phenomena observed in the course of the division of the nucleus show
beyond doubt that an exact halving of its substance is of the greatest
importance. (First shown by W. Roux in 1883.) Compared with the method of
division of the nucleus, that of the cytoplasm appears to be very simple.
This led to the conception that the cell-nucleus must be the chief if not
the sole carrier of hereditary characters in the organism. It is for this
reason that the detailed investigation of fertilisation phenomena
immediately followed researches into the nucleus. The fundamental
discovery of the union of two nuclei in the sexual act was then made (By O.
Hertwig in 1875.) and this afforded a new support for the correct
conception of the nuclear functions. The minute study of the behaviour of
the other constituents of sexual cells during fertilisation led to the
result, that the nucleus alone is concerned with handing on hereditary
characters (This was done by O. Hertwig and the author of this essay
simultaneously in 1884.) from one generation to another. Especially
important, from the point of view of this conclusion, is the study of
fertilisation in Angiosperms (Flowering plants); in these plants the male
sexual cells lose their cell-body in the pollen-tube and the nucleus only--
the sperm-nucleus--reaches the egg. The cytoplasm of the male sexual cell
is therefore not necessary to ensure a transference of hereditary
characters from parents to offspring. I lay stress on the case of the
Angiosperms because researches recently repeated with the help of the
latest methods failed to obtain different results. As regards the
descendants of angiospermous plants, the same laws of heredity hold good as
for other sexually differentiated organisms; we may, therefore, extend to
the latter what the Angiosperms so clearly teach us.

The next advance in the hitherto rapid progress in our knowledge of nuclear
division was delayed, because it was not at once recognised that there are
two absolutely different methods of nuclear division. All such nuclear
divisions were united under the head of indirect or mitotic divisions;
these were also spoken of as karyo-kineses, and were distinguished from the
direct or amitotic divisions which are characterised by a simple
constriction of the nuclear body. So long as the two kinds of indirect
nuclear division were not clearly distinguished, their correct
interpretation was impossible. This was accomplished after long and
laborious research, which has recently been carried out and with results
which should, perhaps, be regarded as provisional.

Soon after the new study of the nucleus began, investigators were struck by
the fact that the course of nuclear division in the mother-cells, or more
correctly in the grandmother-cells, of spores, pollen-grains, and embryo-
sacs of the more highly organised plants and in the spermatozoids and eggs
of the higher animals, exhibits similar phenomena, distinct from those
which occur in the somatic cells.

In the nuclei of all those cells which we may group together as gonotokonts
(At the suggestion of J.P. Lotsy in 1904.) (i.e. cells concerned in
reproduction) there are fewer chromosomes than in the adjacent body-cells
(somatic cells). It was noticed also that there is a peculiarity
characteristic of the gonotokonts, namely the occurrence of two nuclear
divisions rapidly succeeding one another. It was afterwards recognised
that in the first stage of nuclear division in the gonotokonts the
chromosomes unite in pairs: it is these chromosome-pairs, and not the two
longitudinal halves of single chromosomes, which form the nuclear plate in
the equatorial plane of the nuclear spindle. It has been proposed to call
these pairs gemini. (J.E.S. Moore and A.L. Embleton, "Proc. Roy. Soc."
London, Vol. LXXVII. page 555, 1906; V. Gregoire, 1907.) In the course of
this division the spindle-fibrillae attach themselves to the gemini, i.e.
to entire chromosomes and direct them to the points where the new daughter-
nuclei are formed, that is to those positions towards which the
longitudinal halves of the chromosomes travel in ordinary nuclear
divisions. It is clear that in this way the number of chromosomes which
the daughter-nuclei contain, as the result of the first stage in division
in the gonotokonts, will be reduced by one half, while in ordinary
divisions the number of chromosomes always remains the same. The first
stage in the division of the nucleus in the gonotokonts has therefore been
termed the reduction division. (In 1887 W. Flemming termed this the
heterotypic form of nuclear division.) This stage in division determines
the conditions for the second division which rapidly ensues. Each of the
paired chromosomes of the mother-nucleus has already, as in an ordinary
nuclear division, completed the longitudinal fission, but in this case it
is not succeeded by the immediate separation of the longitudinal halves and
their allotment to different nuclei. Each chromosome, therefore, takes its
two longitudinal halves into the same daughter-nucleus. Thus, in each
daughter-nucleus the longitudinal halves of the chromosomes are present
ready for the next stage in the division; they only require to be arranged
in the nuclear plate and then distributed among the granddaughter-nuclei.
This method of division, which takes place with chromosomes already split,
and which have only to provide for the distribution of their longitudinal
halves to the next nuclear generation, has been called homotypic nuclear
division. (The name was proposed by W. Flemming in 1887; the nature of
this type of division was, however, not explained until later.)

Reduction division and homotypic nuclear division are included together
under the term allotypic nuclear division and are distinguished from the
ordinary or typical nuclear division. The name Meiosis (By J. Bretland
Farmer and J.E.S. Moore in 1905.) has also been proposed for these two
allotypic nuclear divisions. The typical divisions are often spoken of as

Observers who were actively engaged in this branch of recent histological
research soon noticed that the chromosomes of a given organism are
differentiated in definite numbers from the nuclear network in the course
of division. This is especially striking in the gonotokonts, but it
applies also to the somatic tissues. In the latter, one usually finds
twice as many chromosomes as in the gonotokonts. Thus the conclusion was
gradually reached that the doubling of chromosomes, which necessarily
accompanies fertilisation, is maintained in the product of fertilisation,
to be again reduced to one half in the gonotokonts at the stage of
reduction-division. This enabled us to form a conception as to the essence
of true alternation of generations, in which generations containing single
and double chromosomes alternate with one another.

The single-chromosome generation, which I will call the HAPLOID, must have
been the primitive generation in all organisms; it might also persist as
the only generation. Every sexual differentiation in organisms, which
occurred in the course of phylogenetic development, was followed by
fertilisation and therefore by the creation of a diploid or double-
chromosome product. So long as the germination of the product of
fertilisation, the zygote, began with a reducing process, a special DIPLOID
generation was not represented. This, however, appeared later as a product
of the further evolution of the zygote, and the reduction division was
correspondingly postponed. In animals, as in plants, the diploid
generation attained the higher development and gradually assumed the
dominant position. The haploid generation suffered a proportional
reduction, until it finally ceased to have an independent existence and
became restricted to the role of producing the sexual products within the
body of the diploid generation. Those who do not possess the necessary
special knowledge are unable to realise what remains of the first haploid
generation in a phanerogamic plant or in a vertebrate animal. In
Angiosperms this is actually represented only by the short developmental
stages which extend from the pollen mother-cells to the sperm-nucleus of
the pollen-tube, and from the embryo-sac mother-cell to the egg and the
endosperm tissue. The embryo-sac remains enclosed in the diploid ovule,
and within this from the fertilised egg is formed the embryo which
introduces the new diploid generation. On the full development of the
diploid embryo of the next generation, the diploid ovule of the preceding
diploid generation is separated from the latter as a ripe seed. The
uninitiated sees in the more highly organised plants only a succession of
diploid generations. Similarly all the higher animals appear to us as
independent organisms with diploid nuclei only. The haploid generation is
confined in them to the cells produced as the result of the reduction
division of the gonotokonts; the development of these is completed with the
homotypic stage of division which succeeds the reduction division and
produces the sexual products.

The constancy of the numbers in which the chromosomes separate themselves
from the nuclear network during division gave rise to the conception that,
in a certain degree, chromosomes possess individuality. Indeed the most
careful investigations (Particularly those of V. Gregoire and his pupils.)
have shown that the segments of the nuclear network, which separate from
one another and condense so as to produce chromosomes for a new division,
correspond to the segments produced from the chromosomes of the preceding
division. The behaviour of such nuclei as possess chromosomes of unequal
size affords confirmatory evidence of the permanence of individual
chromosomes in corresponding sections of an apparently uniform nuclear
network. Moreover at each stage in division chromosomes with the same
differences in size reappear. Other cases are known in which thicker
portions occur in the substance of the resting nucleus, and these agree in
number with the chromosomes. In this network, therefore, the individual
chromosomes must have retained their original position. But the
chromosomes cannot be regarded as the ultimate hereditary units in the
nuclei, as their number is too small. Moreover, related species not
infrequently show a difference in the number of their chromosomes, whereas
the number of hereditary units must approximately agree. We thus picture
to ourselves the carriers of hereditary characters as enclosed in the
chromosomes; the transmitted fixed number of chromosomes is for us only the
visible expression of the conception that the number of hereditary units
which the chromosomes carry must be also constant. The ultimate hereditary
units may, like the chromosomes themselves, retain a definite position in
the resting nucleus. Further, it may be assumed that during the separation
of the chromosomes from one another and during their assumption of the rod-
like form, the hereditary units become aggregated in the chromomeres and
that these are characterised by a constant order of succession. The
hereditary units then grow, divide into two and are uniformly distributed
by the fission of the chromosomes between their longitudinal halves.

As the contraction and rod-like separation of the chromosomes serve to
isnure the transmission of all hereditary units in the products of division
of a nucleus, so, on the other hand, the reticular distension of each
chromosome in the so-called resting nucleus may effect a separation of the
carriers of hereditary units from each other and facilitate the specific
activity of each of them.

In the stages preliminary to their division, the chromosomes become denser
and take up a substance which increases their staining capacity; this is
called chromatin. This substance collects in the chromomeres and may form
the nutritive material for the carriers of hereditary units which we now
believe to be enclosed in them. The chromatin cannot itself be the
hereditary substance, as it afterwards leaves the chromosomes, and the
amount of it is subject to considerable variation in the nucleus, according
to its stage of development. Conjointly with the materials which take part
in the formation of the nuclear spindle and other processes in the cell,
the chromatin accumulates in the resting nucleus to form the nucleoli.

Naturally connected with the conclusion that the nuclei are the carriers of
hereditary characters in the organism, is the question whether enucleate
organisms can also exist. Phylogenetic considerations give an affirmative
answer to this question. The differentiation into nucleus and cytoplasm
represents a division of labour in the protoplast. A study of organisms
which belong to the lowest class of the organic world teaches us how this
was accomplished. Instead of well-defined nuclei, scattered granules have
been described in the protoplasm of several of these organisms (Bacteria,
Cyanophyceae, Protozoa.), characterised by the same reactions as nuclear
material, provided also with a nuclear network, but without a limiting
membrane. (This is the result of the work of R. Hertwig and of the most
recently published investigations.) Thus the carriers of hereditary
characters may originally have been distributed in the common protoplasm,
afterwards coming together and eventually assuming a definite form as
special organs of the cell. It may be also assumed that in the protoplasm
and in the primitive types of nucleus, the carriers of the same hereditary
unit were represented in considerable quantity; they became gradually
differentiated to an extent commensurate with newly acquired characters.
It was also necessary that, in proportion as this happened, the mechanism
of nuclear division must be refined. At first processes resembling a
simple constriction would suffice to provide for the distribution of all
hereditary units to each of the products of division, but eventually in
both organic kingdoms nuclear division, which alone insured the qualitative
identity of the products of division, became a more marked feature in the
course of cell-multiplication.

Where direct nuclear division occurs by constriction in the higher
organisms, it does not result in the halving of hereditary units. So far
as my observations go, direct nuclear division occurs in the more highly
organised plants only in cells which have lost their specific functions.
Such cells are no longer capable of specific reproduction. An interesting
case in this connection is afforded by the internodal cells of the
Characeae, which possess only vegetative functions. These cells grow
vigorously and their cytoplasm increases, their growth being accompanied by
a correspondingly direct multiplication of the nuclei. They serve chiefly
to nourish the plant, but, unlike the other cells, they are incapable of
producing any offspring. This is a very instructive case, because it
clearly shows that the nuclei are not only carriers of hereditary
characters, but that they also play a definite part in the metabolism of
the protoplasts.

Attention was drawn to the fact that during the reducing division of nuclei
which contain chromosomes of unequal size, gemini are constantly produced
by the pairing of chromosomes of the same size. This led to the conclusion
that the pairing chromosomes are homologous, and that one comes from the
father, the other from the mother. (First stated by T.H. Montgomery in
1901 and by W.S. Sutton in 1902.) This evidently applies also to the
pairing of chromosomes in those reduction-divisions in which differences in
size do not enable us to distinguish the individual chromosomes. In this
case also each pair would be formed by two homologous chromosomes, the one
of paternal, the other of maternal origin. When the separation of these
chromosomes and their distribution to both daughter-nuclei occur a
chromosome of each kind is provided for each of these nuclei. It would
seem that the components of each pair might pass to either pole of the
nuclear spindle, so that the paternal and maternal chromosomes would be
distributed in varying proportion between the daughter-nuclei; and it is
not impossible that one daughter-nucleus might occasionally contain
paternal chromosomes only and its sister-nucleus exclusively maternal

The fact that in nuclei containing chromosomes of various sizes, the
chromosomes which pair together in reduction-division are always of equal
size, constitutes a further and more important proof of their qualitative
difference. This is supported also by ingenious experiments which led to
an unequal distribution of chromosomes in the products of division of a
sea-urchin's egg, with the result that a difference was induced in their
further development. (Demonstrated by Th. Boveri in 1902.)

The recently discovered fact that in diploid nuclei the chromosomes are
arranged in pairs affords additional evidence in favour of the unequal
value of the chromosomes. This is still more striking in the case of
chromosomes of different sizes. It has been shown that in the first
division-figure in the nucleus of the fertilised egg the chromosomes of
corresponding size form pairs. They appear with this arrangement in all
subsequent nuclear divisions in the diploid generation. The longitudinal
fissions of the chromosomes provide for the unaltered preservation of this
condition. In the reduction nucleus of the gonotokonts the homologous
chromosomes being near together need not seek out one another; they are
ready to form gemini. The next stage is their separation to the haploid
daughter-nuclei, which have resulted from the reduction process.

Peculiar phenomena in the reduction nucleus accompany the formation of
gemini in both organic kingdoms. (This has been shown more particularly by
the work of L. Guignard, M. Mottier, J.B. Farmer, C.B. Wilson, V. Hacker
and more recently by V. Gregoire and his pupil C.A. Allen, by the
researches conducted in the Bonn Botanical Institute, and by A. and K.E.
Schreiner.) Probably for the purpose of entering into most intimate
relation, the pairs are stretched to long threads in which the chromomeres
come to lie opposite one another. (C.A. Allen, A. and K.E. Schreiner, and
Strasburger.) It seems probable that these are homologous chromomeres, and
that the pairs afterwards unite for a short time, so that an exchange of
hereditary units is rendered possible. (H. de Vries and Strasburger.)
This cannot be actually seen, but certain facts of heredity point to the
conclusion that this occurs. It follows from these phenomena that any
exchange which may be effected must be one of homologous carriers of
hereditary units only. These units continue to form exchangeable segments
after they have undergone unequal changes; they then constitute
allelotropic pairs. We may thus calculate what sum of possible
combinations the exchange of homologous hereditary units between the
pairing chromosomes provides for before the reduction division and the
subsequent distribution of paternal and maternal chromosomes in the haploid
daughter-nuclei. These nuclei then transmit their characters to the sexual
cells, the conjugation of which in fertilization again produces the most
varied combinations. (A. Weismann gave the impulse to these ideas in his
theory on "Amphimixis".) In this way all the cooperations which the
carriers of hereditary characters are capable of in a species are produced;
this must give it an appreciable advantage in the struggle for life.

The admirers of Charles Darwin must deeply regret that he did not live to
see the results achieved by the new Cytology. What service would they have
been to him in the presentation of his hypothesis of Pangenesis; what an
outlook into the future would they have given to his active mind!

The Darwinian hypothesis of Pangenesis rests on the conception that all
inheritable properties are represented in the cells by small invisible
particles or gemmules and that these gemmules increase by division.
Cytology began to develop on new lines some years after the publication in
1868 of Charles Darwin's "Provisional hypothesis of Pangenesis" ("Animals
and Plants under Domestication", London, 1868, Chapter XXVII.), and when he
died in 1882 it was still in its infancy. Darwin would have soon suggested
the substitution of the nuclei for his gemmules. At least the great
majority of present-day investigators in the domain of cytology have been
led to the conclusion that the nucleus is the carrier of hereditary
characters, and they also believe that hereditary characters are
represented in the nucleus as distinct units. Such would be Darwin's
gemmules, which in conformity with the name of his hypothesis may be called
pangens (So called by H. de Vries in 1889.): these pangens multiply by
division. All recently adopted views may be thus linked on to this part of
Darwin's hypothesis. It is otherwise with Darwin's conception to which
Pangenesis owes its name, namely the view that all cells continually give
off gemmules, which migrate to other places in the organism, where they
unite to form reproductive cells. When Darwin foresaw this possibility,
the continuity of the germinal substance was still unknown (Demonstrated by
Nussbaum in 1880, by Sachs in 1882, and by Weismann in 1885.), a fact which
excludes a transference of gemmules.

But even Charles Darwin's genius was confined within finite boundaries by
the state of science in his day.

It is not my province to deal with other theories of development which
followed from Darwin's Pangenesis, or to discuss their histological
probabilities. We can, however, affirm that Charles Darwin's idea that
invisible gemmules are the carriers of hereditary characters and that they
multiply by division has been removed from the position of a provisional
hypothesis to that of a well-founded theory. It is supported by histology,
and the results of experimental work in heredity, which are now assuming
extraordinary prominence, are in close agreement with it.


Professor of Anatomy in the University of Strassburg.

The problem of the origin of the human race, of the descent of man, is
ranked by Huxley in his epoch-making book "Man's Place in Nature", as the
deepest with which biology has to concern itself, "the question of
questions,"--the problem which underlies all others. In the same brilliant
and lucid exposition, which appeared in 1863, soon after the publication of
Darwin's "Origin of Species", Huxley stated his own views in regard to this
great problem. He tells us how the idea of a natural descent of man
gradually grew up in his mind, it was especially the assertions of Owen in
regard to the total difference between the human and the simian brain that
called forth strong dissent from the great anatomist Huxley, and he easily
succeeded in showing that Owen's supposed differences had no real
existence; he even established, on the basis of his own anatomical
investigations, the proposition that the anatomical differences between the
Marmoset and the Chimpanzee are much greater than those between the
Chimpanzee and Man.

But why do we thus introduce the study of Darwin's "Descent of Man", which
is to occupy us here, by insisting on the fact that Huxley had taken the
field in defence of the descent of man in 1863, while Darwin's book on the
subject did not appear till 1871? It is in order that we may clearly
understand how it happened that from this time onwards Darwin and Huxley
followed the same great aim in the most intimate association.

Huxley and Darwin working at the same Problema maximum! Huxley fiery,
impetuous, eager for battle, contemptuous of the resistance of a dull
world, or energetically triumphing over it. Darwin calm, weighing every
problem slowly, letting it mature thoroughly,--not a fighter, yet having
the greater and more lasting influence by virtue of his immense mass of
critically sifted proofs. Darwin's friend, Huxley, was the first to do him
justice, to understand his nature, and to find in it the reason why the
detailed and carefully considered book on the descent of man made its
appearance so late. Huxley, always generous, never thought of claiming
priority for himself. In enthusiastic language he tells how Darwin's
immortal work, "The Origin of Species", first shed light for him on the
problem of the descent of man; the recognition of a vera causa in the
transformation of species illuminated his thoughts as with a flash. He was
now content to leave what perplexed him, what he could not yet solve, as he
says himself, "in the mighty hands of Darwin." Happy in the bustle of
strife against old and deep-rooted prejudices, against intolerance and
superstition, he wielded his sharp weapons on Darwin's behalf; wearing
Darwin's armour he joyously overthrew adversary after adversary. Darwin
spoke of Huxley as his "general agent." ("Life and Letters of Thomas Henry
Huxley", Vol. I. page 171, London, 1900.) Huxley says of himself "I am
Darwin's bulldog." (Ibid. page 363.)

Thus Huxley openly acknowledged that it was Darwin's "Origin of Species"
that first set the problem of the descent of man in its true light, that
made the question of the origin of the human race a pressing one. That
this was the logical consequence of his book Darwin himself had long felt.
He had been reproached with intentionally shirking the application of his
theory to Man. Let us hear what he says on this point in his
autobiography: "As soon as I had become, in the year 1837 or 1838,
convinced that species were mutable productions, I could not avoid the
belief that man must come under the same law. Accordingly I collected
notes on the subject for my own satisfaction, and not for a long time with
any intention of publishing. Although in the 'Origin of Species' the
derivation of any particular species is never discussed, yet I thought it
VIEWS (No italics in original.), to add that by the work 'light would be
thrown on the origin of man and his history.' It would have been useless
and injurious to the success of the book to have paraded, without giving
any evidence, my conviction with respect to his origin." ("Life and
Letters of Charles Darwin", Vol. 1. page 93.)

In a letter written in January, 1860, to the Rev. L. Blomefield, Darwin
expresses himself in similar terms. "With respect to man, I am very far
from wishing to obtrude my belief; but I thought it dishonest to quite
conceal my opinion." (Ibid. Vol. II. page 263.)

The brief allusion in the "Origin of Species" is so far from prominent and
so incidental that it was excusable to assume that Darwin had not touched
upon the descent of man in this work. It was solely the desire to have his
mass of evidence sufficiently complete, solely Darwin's great
characteristic of never publishing till he had carefully weighed all
aspects of his subject for years, solely, in short, his most fastidious
scientific conscience that restrained him from challenging the world in
1859 with a book in which the theory of the descent of man was fully set
forth. Three years, frequently interrupted by ill-health, were needed for
the actual writing of the book ("Life and Letters", Vol. I. page 94.): the
first edition, which appeared in 1871, was followed in 1874 by a much
improved second edition, the preparation of which he very reluctantly
undertook. (Ibid. Vol. III. page 175.)

This, briefly, is the history of the work, which, with the "Origin of
Species", marks an epoch in the history of biological sciences--the work
with which the cautious, peace-loving investigator ventured forth from his
contemplative life into the arena of strife and unrest, and laid himself
open to all the annoyances that deep-rooted belief and prejudice, and the
prevailing tendency of scientific thought at the time could devise.

Darwin did not take this step lightly. Of great interest in this
connection is a letter written to Wallace on Dec. 22, 1857 (Ibid. Vol. II.
page 109.), in which he says "You ask whether I shall discuss 'man.' I
think I shall avoid the whole subject, as so surrounded with prejudices;
though I fully admit that it is the highest and most interesting problem
for the naturalist." But his conscientiousness compelled him to state
briefly his opinion on the subject in the "Origin of Species" in 1859.
Nevertheless he did not escape reproaches for having been so reticent.
This is unmistakably apparent from a letter to Fritz Muller dated February
22 (1869?), in which he says: "I am thinking of writing a little essay on
the Origin of Mankind, as I have been taunted with concealing my opinions."
(Ibid. Vol. III. page 112.)

It might be thought that Darwin behaved thus hesitatingly, and was so slow
in deciding on the full publication of his collected material in regard to
the descent of man, because he had religious difficulties to overcome.

But this was not the case, as we can see from his admirable confession of
faith, the publication of which we owe to his son Francis. (Ibid. Vol. I.
pages 304-317.) Whoever wishes really to understand the lofty character of
this great man should read these immortal lines in which he unfolds to us
in simple and straightforward words the development of his conception of
the universe. He describes how, though he was still quite orthodox during
his voyage round the world on board the "Beagle", he came gradually to see,
shortly afterwards (1836-1839) that the Old Testament was no more to be
trusted than the Sacred Books of the Hindoos; the miracles by which
Christianity is supported, the discrepancies between the accounts in the
different Gospels, gradually led him to disbelieve in Christianity as a
divine revelation. "Thus," he writes ("Life and Letters", Vol. 1. page
309.), "disbelief crept over me at a very slow rate, but was at last
complete. The rate was so slow that I felt no distress." But Darwin was
too modest to presume to go beyond the limits laid down by science. He
wanted nothing more than to be able to go, freely and unhampered by belief
in authority or in the Bible, as far as human knowledge could lead him. We
learn this from the concluding words of his chapter on religion: "The
mystery of the beginning of all things is insoluble by us; and I for one
must be content to remain an Agnostic." (Loc. cit. page 313.)

Darwin was always very unwilling to give publicity to his views in regard
to religion. In a letter to Asa Gray on May 22, 1860 (Ibid. Vol. II. page
310.), he declares that it is always painful to him to have to enter into
discussion of religious problems. He had, he said, no intention of writing

Finally, let us cite one characteristic sentence from a letter from Darwin
to C. Ridley (Ibid. Vol. III. page. 236. ("C. Ridley," Mr Francis Darwin
points out to me, should be H.N. Ridley. A.C.S.)) (Nov. 28, 1878.) A
clergyman, Dr Pusey, had asserted that Darwin had written the "Origin of
Species" with some relation to theology. Darwin writes emphatically, "Many
years ago, when I was collecting facts for the 'Origin', my belief in what
is called a personal God was as firm as that of Dr Pusey himself, and as to
the eternity of matter I never troubled myself about such insoluble
questions." The expression "many years ago" refers to the time of his
voyage round the world, as has already been pointed out. Darwin means by
this utterance that the views which had gradually developed in his mind in
regard to the origin of species were quite compatible with the faith of the

If we consider all these utterances of Darwin in regard to religion and to
his outlook on life (Weltanschauung), we shall see at least so much, that
religious reflection could in no way have influenced him in regard to the
writing and publishing of his book on "The Descent of Man". Darwin had
early won for himself freedom of thought, and to this freedom he remained
true to the end of his life, uninfluenced by the customs and opinions of
the world around him.

Darwin was thus inwardly fortified and armed against the host of calumnies,
accusations, and attacks called forth by the publication of the "Origin of
Species", and to an even greater extent by the appearance of the "Descent
of Man". But in his defence he could rely on the aid of a band of
distinguished auxiliaries of the rarest ability. His faithful confederate,
Huxley, was joined by the botanist Hooker, and, after longer resistance, by
the famous geologist Lyell, whose "conversion" afforded Darwin peculiar
satisfaction. All three took the field with enthusiasm in defence of the
natural descent of man. From Wallace, on the other hand, though he shared
with him the idea of natural selection, Darwin got no support in this
matter. Wallace expressed himself in a strange manner. He admitted
everything in regard to the morphological descent of man, but maintained,
in a mystic way, that something else, something of a spiritual nature must
have been added to what man inherited from his animal ancestors. Darwin,
whose esteem for Wallace was extraordinarily high, could not understand how
he could give utterance to such a mystical view in regard to man; the idea
seemed to him so "incredibly strange" that he thought some one else must
have added these sentences to Wallace's paper.

Even now there are thinkers who, like Wallace, shrink from applying to man
the ultimate consequences of the theory of descent. The idea that man is
derived from ape-like forms is to them unpleasant and humiliating.

So far I have been depicting the development of Darwin's work on the
descent of man. In what follows I shall endeavour to give a condensed
survey of the contents of the book.

It must at once be said that the contents of Darwin's work fall into two
parts, dealing with entirely different subjects. "The Descent of Man"
includes a very detailed investigation in regard to secondary sexual
characters in the animal series, and on this investigation Darwin founded a
new theory, that of sexual selection. With astonishing patience he
gathered together an immense mass of material, and showed, in regard to
Arthropods and Vertebrates, the wide distribution of secondary characters,
which develop almost exclusively in the male, and which enable him, on the
one hand, to get the better of his rivals in the struggle for the female by
the greater perfection of his weapons, and on the other hand, to offer
greater allurements to the female through the higher development of
decorative characters, of song, or of scent-producing glands. The best
equipped males will thus crowd out the less well-equipped in the matter of
reproduction, and thus the relevant characters will be increased and
perfected through sexual selection. It is, of course, a necessary
assumption that these secondary sexual characters may be transmitted to the
female, although perhaps in rudimentary form.

As we have said, this theory of sexual selection takes up a great deal of
space in Darwin's book, and it need only be considered here in so far as
Darwin applied it to the descent of man. To this latter problem the whole
of Part I is devoted, while Part III contains a discussion of sexual
selection in relation to man, and a general summary. Part II treats of
sexual selection in general, and may be disregarded in our present study.
Moreover, many interesting details must necessarily be passed over in what
follows, for want of space.

The first part of the "Descent of Man" begins with an enumeration of the
proofs of the animal descent of man taken from the structure of the human
body. Darwin chiefly emphasises the fact that the human body consists of
the same organs and of the same tissues as those of the other mammals; he
shows also that man is subject to the same diseases and tormented by the
same parasites as the apes. He further dwells on the general agreement
exhibited by young, embryonic forms, and he illustrates this by two figures
placed one above the other, one representing a human embryo, after Eaker,
the other a dog embryo, after Bischoff. ("Descent of Man" (Popular
Edition, 1901), fig. 1, page 14.)

Darwin finds further proofs of the animal origin of man in the reduced
structures, in themselves extremely variable, which are either absolutely
useless to their possessors, or of so little use that they could never have
developed under existing conditions. Of such vestiges he enumerates: the
defective development of the panniculus carnosus (muscle of the skin) so
widely distributed among mammals, the ear-muscles, the occasional
persistence of the animal ear-point in man, the rudimentary nictitating
membrane (plica semilunaris) in the human eye, the slight development of
the organ of smell, the general hairiness of the human body, the frequently
defective development or entire absence of the third molar (the wisdom
tooth), the vermiform appendix, the occasional reappearance of a bony canal
(foramen supracondyloideum) at the lower end of the humerus, the
rudimentary tail of man (the so-called taillessness), and so on. Of these
rudimentary structures the occasional occurrence of the animal ear-point in
man is most fully discussed. Darwin's attention was called to this
interesting structure by the sculptor Woolner. He figures such a case
observed in man, and also the head of an alleged orang-foetus, the
photograph of which he received from Nitsche.

Darwin's interpretation of Woolner's case as having arisen through a
folding over of the free edge of a pointed ear has been fully borne out by
my investigations on the external ear. (G. Schwalbe, "Das Darwin'sche
Spitzohr beim menschlichen Embryo", "Anatom. Anzeiger", 1889, pages 176-
189, and other papers.) In particular, it was established by these
investigations that the human foetus, about the middle of its embryonic
life, possesses a pointed ear somewhat similar to that of the monkey genus
Macacus. One of Darwin's statements in regard to the head of the orang-
foetus must be corrected. A LARGE ear with a point is shown in the
photograph ("Descent of Man", fig.3, page 24.), but it can easily be
demonstrated--and Deniker has already pointed this out--that the figure is
not that of an orang-foetus at all, for that form has much smaller ears
with no point; nor can it be a gibbon-foetus, as Deniker supposes, for the
gibbon ear is also without a point. I myself regard it as that of a
Macacus-embryo. But this mistake, which is due to Nitsche, in no way
affects the fact recognised by Darwin, that ear-forms showing the point
characteristic of the animal ear occur in man with extraordinary frequency.

Finally, there is a discussion of those rudimentary structures which occur
only in ONE sex, such as the rudimentary mammary glands in the male, the
vesicula prostatica, which corresponds to the uterus of the female, and
others. All these facts tell in favour of the common descent of man and
all other vertebrates. The conclusion of this section is characteristic:
(Ibid. page 36.)

In the second chapter there is a more detailed discussion, again based upon
an extraordinary wealth of facts, of the problem as to the manner in which,
and the causes through which, man evolved from a lower form. Precisely the
same causes are here suggested for the origin of man, as for the origin of
species in general. Variability, which is a necessary assumption in regard
to all transformations, occurs in man to a high degree. Moreover, the
rapid multiplication of the human race creates conditions which necessitate
an energetic struggle for existence, and thus afford scope for the
intervention of natural selection. Of the exercise of ARTIFICIAL selection
in the human race, there is nothing to be said, unless we cite such cases
as the grenadiers of Frederick William I, or the population of ancient
Sparta. In the passages already referred to and in those which follow, the
transmission of acquired characters, upon which Darwin does not dwell, is
taken for granted. In man, direct effects of changed conditions can be
demonstrated (for instance in regard to bodily size), and there are also
proofs of the influence exerted on his physical constitution by increased
use or disuse. Reference is here made to the fact, established by Forbes,
that the Quechua-Indians of the high plateaus of Peru show a striking
development of lungs and thorax, as a result of living constantly at high

Such special forms of variation as arrests of development (microcephalism)
and reversion to lower forms are next discussed. Darwin himself felt
("Descent of Man", page 54.) that these subjects are so nearly related to
the cases mentioned in the first chapter, that many of them might as well
have been dealt with there. It seems to me that it would have been better
so, for the citation of additional instances of reversion at this place
rather disturbs the logical sequence of his ideas as to the conditions
which have brought about the evolution of man from lower forms. The
instances of reversion here discussed are microcephalism, which Darwin
wrongly interpreted as atavistic, supernumerary mammae, supernumerary
digits, bicornuate uterus, the development of abnormal muscles, and so on.
Brief mention is also made of correlative variations observed in man.

Darwin next discusses the question as to the manner in which man attained
to the erect position from the state of a climbing quadruped. Here again
he puts the influence of Natural Selection in the first rank. The
immediate progenitors of man had to maintain a struggle for existence in
which success was to the more intelligent, and to those with social
instincts. The hand of these climbing ancestors, which had little skill
and served mainly for locomotion, could only undergo further development
when some early member of the Primate series came to live more on the
ground and less among trees.

A bipedal existence thus became possible, and with it the liberation of the
hand from locomotion, and the one-sided development of the human foot. The
upright position brought about correlated variations in the bodily
structure; with the free use of the hand it became possible to manufacture
weapons and to use them; and this again resulted in a degeneration of the
powerful canine teeth and the jaws, which were then no longer necessary for
defence. Above all, however, the intelligence immediately increased, and
with it skull and brain. The nakedness of man, and the absence of a tail
(rudimentariness of the tail vertebrae) are next discussed. Darwin is
inclined to attribute the nakedness of man, not to the action of natural
selection on ancestors who originally inhabited a tropical land, but to
sexual selection, which, for aesthetic reasons, brought about the loss of
the hairy covering in man, or primarily in woman. An interesting
discussion of the loss of the tail, which, however, man shares with the
anthropoid apes, some other monkeys and lemurs, forms the conclusion of the
almost superabundant material which Darwin worked up in the second chapter.
His object was to show that some of the most distinctive human characters
are in all probability directly or indirectly due to natural selection.
With characteristic modesty he adds ("Descent of Man", page 92.): "Hence,
if I have erred in giving to natural selection great power, which I am very
far from admitting, or in having exaggerated its power, which is in itself
probable, I have at least, as I hope, done good service in aiding to
overthrow the dogma of separate creations." At the end of the chapter he
touches upon the objection as to man's helpless and defenceless condition.
Against this he urges his intelligence and social instincts.

The two following chapters contain a detailed discussion of the objections
drawn from the supposed great differences between the mental powers of men
and animals. Darwin at once admits that the differences are enormous, but
not that any fundamental difference between the two can be found. Very
characteristic of him is the following passage: "In what manner the mental
powers were first developed in the lowest organisms, is as hopeless an
enquiry as how life itself first originated. These are problems for the
distant future, if they are ever to be solved by man." (Ibid. page 100.)

After some brief observations on instinct and intelligence, Darwin brings
forward evidence to show that the greater number of the emotional states,
such as pleasure and pain, happiness and misery, love and hate are common
to man and the higher animals. He goes on to give various examples showing
that wonder and curiosity, imitation, attention, memory and imagination
(dreams of animals), can also be observed in the higher mammals, especially
in apes. In regard even to reason there are no sharply defined limits. A
certain faculty of deliberation is characteristic of some animals, and the
more thoroughly we know an animal the more intelligence we are inclined to
credit it with. Examples are brought forward of the intelligent and
deliberate actions of apes, dogs and elephants. But although no sharply
defined differences exist between man and animals, there is, nevertheless,
a series of other mental powers which are characteristics usually regarded
as absolutely peculiar to man. Some of these characteristics are examined
in detail, and it is shown that the arguments drawn from them are not
conclusive. Man alone is said to be capable of progressive improvement;
but against this must be placed as something analogous in animals, the fact
that they learn cunning and caution through long continued persecution.
Even the use of tools is not in itself peculiar to man (monkeys use sticks,
stones and twigs), but man alone fashions and uses implements DESIGNED FOR
A SPECIAL PURPOSE. In this connection the remarks taken from Lubbock in
regard to the origin and gradual development of the earliest flint
implements will be read with interest; these are similar to the
observations on modern eoliths, and their bearing on the development of the
stone-industry. It is interesting to learn from a letter to Hooker ("Life
and Letters", Vol. II. page 161, June 22, 1859.), that Darwin himself at
first doubted whether the stone implements discovered by Boucher de Perthes
were really of the nature of tools. With the relentless candour as to
himself which characterised him, he writes four years later in a letter to
Lyell in regard to this view of Boucher de Perthes' discoveries: "I know
something about his errors, and looked at his book many years ago, and am
ashamed to think that I concluded the whole was rubbish! Yet he has done
for man something like what Agassiz did for glaciers." (Ibid. Vol. III.
page 15, March 17, 1863.)

To return to Darwin's further comparisons between the higher mental powers
of man and animals. He takes much of the force from the argument that man
alone is capable of abstraction and self-consciousness by his own
observations on dogs. One of the main differences between man and animals,
speech, receives detailed treatment. He points out that various animals
(birds, monkeys, dogs) have a large number of different sounds for
different emotions, that, further, man produces in common with animals a
whole series of inarticulate cries combined with gestures, and that dogs
learn to understand whole sentences of human speech. In regard to human
language, Darwin expresses a view contrary to that held by Max Muller
("Descent of Man", page 132.): "I cannot doubt that language owes its
origin to the imitation and modification of various natural sounds, the
voices of other animals, and man's own instinctive cries, aided by signs
and gestures." The development of actual language presupposes a higher
degree of intelligence than is found in any kind of ape. Darwin remarks on
this point (Ibid. pages 136, 137.): "The fact of the higher apes not using
their vocal organs for speech no doubt depends on their intelligence not
having been sufficiently advanced."

The sense of beauty, too, has been alleged to be peculiar to man. In
refutation of this assertion Darwin points to the decorative colours of
birds, which are used for display. And to the last objection, that man
alone has religion, that he alone has a belief in God, it is answered "that
numerous races have existed, and still exist, who have no idea of one or
more gods, and who have no words in their languages to express such an
idea." (Ibid. page 143.)

The result of the investigations recorded in this chapter is to show that,
great as the difference in mental powers between man and the higher animals
may be, it is undoubtedly only a difference "of degree and not of kind."
("Descent of Man", page 193.)

In the fourth chapter Darwin deals with the MORAL SENSE or CONSCIENCE,
which is the most important of all differences between man and animals. It
is a result of social instincts, which lead to sympathy for other members
of the same society, to non-egoistic actions for the good of others.
Darwin shows that social tendencies are found among many animals, and that
among these love and kin-sympathy exist, and he gives examples of animals
(especially dogs) which may exhibit characters that we should call moral in
man (e.g. disinterested self-sacrifice for the sake of others). The early
ape-like progenitors of the human race were undoubtedly social. With the
increase of intelligence the moral sense develops farther; with the
acquisition of speech public opinion arises, and finally, moral sense
becomes habit. The rest of Darwin's detailed discussions on moral
philosophy may be passed over.

The fifth chapter may be very briefly summarised. In it Darwin shows that
the intellectual and moral faculties are perfected through natural
selection. He inquires how it can come about that a tribe at a low level
of evolution attains to a higher, although the best and bravest among them
often pay for their fidelity and courage with their lives without leaving
any descendants. In this case it is the sentiment of glory, praise and
blame, the admiration of others, which bring about the increase of the
better members of the tribe. Property, fixed dwellings, and the
association of families into a community are also indispensable
requirements for civilisation. In the longer second section of the fifth
chapter Darwin acts mainly as recorder. On the basis of numerous
investigations, especially those of Greg, Wallace, and Galton, he inquires
how far the influence of natural selection can be demonstrated in regard to
civilised nations. In the final section, which deals with the proofs that
all civilised nations were once barbarians, Darwin again uses the results
gained by other investigators, such as Lubbock and Tylor. There are two
sets of facts which prove the proposition in question. In the first place,
we find traces of a former lower state in the customs and beliefs of all
civilised nations, and in the second place, there are proofs to show that
savage races are independently able to raise themselves a few steps in the
scale of civilisation, and that they have thus raised themselves.

In the sixth chapter of the work, Morphology comes into the foreground once
more. Darwin first goes back, however, to the argument based on the great
difference between the mental powers of the highest animals and those of
man. That this is only quantitative, not qualitative, he has already
shown. Very instructive in this connection is the reference to the
enormous difference in mental powers in another class. No one would draw
from the fact that the cochineal insect (Coccus) and the ant exhibit
enormous differences in their mental powers, the conclusion that the ant
should therefore be regarded as something quite distinct, and withdrawn
from the class of insects altogether.

Darwin next attempts to establish the SPECIFIC genealogical tree of man,
and carefully weighs the differences and resemblances between the different
families of the Primates. The erect position of man is an adaptive
character, just as are the various characters referable to aquatic life in
the seals, which, notwithstanding these, are ranked as a mere family of the
Carnivores. The following utterance is very characteristic of Darwin
("Descent of Man", page 231.): "If man had not been his own classifier, he
would never have thought of founding a separate order for his own
reception." In numerous characters not mentioned in systematic works, in
the features of the face, in the form of the nose, in the structure of the
external ear, man resembles the apes. The arrangement of the hair in man
has also much in common with the apes; as also the occurrence of hair on
the forehead of the human embryo, the beard, the convergence of the hair of
the upper and under arm towards the elbow, which occurs not only in the
anthropoid apes, but also in some American monkeys. Darwin here adopts
Wallace's explanation of the origin of the ascending direction of the hair
in the forearm of the orang,--that it has arisen through the habit of
holding the hands over the head in rain. But this explanation cannot be
maintained when we consider that this disposition of the hair is widely
distributed among the most different mammals, being found in the dog, in
the sloth, and in many of the lower monkeys.

After further careful analysis of the anatomical characters Darwin reaches
the conclusion that the New World monkeys (Platyrrhine) may be excluded
from the genealogical tree altogether, but that man is an offshoot from the
Old World monkeys (Catarrhine) whose progenitors existed as far back as the
Miocene period. Among these Old World monkeys the forms to which man shows
the greatest resemblance are the anthropoid apes, which, like him, possess
neither tail nor ischial callosities. The platyrrhine and catarrhine
monkeys have their primitive ancestor among extinct forms of the Lemuridae.
Darwin also touches on the question of the original home of the human race
and supposes that it may have been in Africa, because it is there that
man's nearest relatives, the gorilla and the chimpanzee, are found. But he
regards speculation on this point as useless. It is remarkable that, in
this connection, Darwin regards the loss of the hair-covering in man as
having some relation to a warm climate, while elsewhere he is inclined to
make sexual selection responsible for it. Darwin recognises the great gap
between man and his nearest relatives, but similar gaps exist at other
parts of the mammalian genealogical tree: the allied forms have become
extinct. After the extermination of the lower races of mankind, on the one
hand, and of the anthropoid apes on the other, which will undoubtedly take
place, the gulf will be greater than ever, since the baboons will then
bound it on the one side, and the white races on the other. Little weight
need be attached to the lack of fossil remains to fill up this gap, since
the discovery of these depends upon chance. The last part of the chapter
is devoted to a discussion of the earlier stages in the genealogy of man.
Here Darwin accepts in the main the genealogical tree, which had meantime
been published by Haeckel, who traces the pedigree back through Monotremes,
Reptiles, Amphibians, and Fishes, to Amphioxus.

Then follows an attempt to reconstruct, from the atavistic characters, a
picture of our primitive ancestor who was undoubtedly an arboreal animal.
The occurrence of rudiments of parts in one sex which only come to full
development in the other is next discussed. This state of things Darwin
regards as derived from an original hermaphroditism. In regard to the
mammary glands of the male he does not accept the theory that they are
vestigial, but considers them rather as not fully developed.

The last chapter of Part I deals with the question whether the different
races of man are to be regarded as different species, or as sub-species of
a race of monophyletic origin. The striking differences between the races
are first emphasised, and the question of the fertility or infertility of
hybrids is discussed. That fertility is the more usual is shown by the
excessive fertility of the hybrid population of Brazil. This, and the
great variability of the distinguishing characters of the different races,
as well as the fact that all grades of transition stages are found between
these, while considerable general agreement exists, tell in favour of the
unity of the races and lead to the conclusion that they all had a common
primitive ancestor.

Darwin therefore classifies all the different races as sub-species of ONE
AND THE SAME SPECIES. Then follows an interesting inquiry into the reasons
for the extinction of human races. He recognises as the ultimate reason
the injurious effects of a change of the conditions of life, which may
bring about an increase in infantile mortality, and a diminished fertility.
It is precisely the reproductive system, among animals also, which is most
susceptible to changes in the environment.

The final section of this chapter deals with the formation of the races of
mankind. Darwin discusses the question how far the direct effect of
different conditions of life, or the inherited effects of increased use or
disuse may have brought about the characteristic differences between the
different races. Even in regard to the origin of the colour of the skin he
rejects the transmitted effects of an original difference of climate as an
explanation. In so doing he is following his tendency to exclude
Lamarckian explanations as far as possible. But here he makes gratuitous
difficulties from which, since natural selection fails, there is no escape
except by bringing in the principle of sexual selection, to which, he
regarded it as possible, skin-colouring, arrangement of hair, and form of
features might be traced. But with his characteristic conscientiousness he
guards himself thus: "I do not intend to assert that sexual selection will
account for all the differences between the races." ("Descent of Man",
page 308.)

I may be permitted a remark as to Darwin's attitude towards Lamarck.
While, at an earlier stage, when he was engaged in the preliminary labours
for his immortal work, "The Origin of Species", Darwin expresses himself
very forcibly against the views of Lamarck, speaking of Lamarckian
"nonsense," ("Life and Letters", Vol. II. page 23.), and of Lamarck's
"absurd, though clever work" (Loc. cit. page 39.) and expressly declaring,
"I attribute very little to the direct action of climate, etc." (Loc. cit.
(1856), page 82.) yet in later life he became more and more convinced of
the influence of external conditions. In 1876, that is, two years after
the appearance of the second edition of "The Descent of Man", he writes
with his usual candid honesty: "In my opinion the greatest error which I
have committed, has been not allowing sufficient weight to the direct
action of the environment, i.e. food, climate, etc. independently of
natural selection." (Ibid. Vol. III. page 159.) It is certain from this
change of opinion that, if he had been able to make up his mind to issue a
third edition of "The Descent of Man", he would have ascribed a much
greater influence to the effect of external conditions in explaining the
different characters of the races of man than he did in the second edition.
He would also undoubtedly have attributed less influence to sexual
selection as a factor in the origin of the different bodily
characteristics, if indeed he would not have excluded it altogether.

In Part III of the "Descent" two additional chapters are devoted to the
discussion of sexual selection in relation to man. These may be very
briefly referred to. Darwin here seeks to show that sexual selection has
been operative on man and his primitive progenitor. Space fails me to
follow out his interesting arguments. I can only mention that he is
inclined to trace back hairlessness, the development of the beard in man,
and the characteristic colour of the different human races to sexual
selection. Since bareness of the skin could be no advantage, but rather a
disadvantage, this character cannot have been brought about by natural
selection. Darwin also rejected a direct influence of climate as a cause
of the origin of the skin-colour. I have already expressed the opinion,
based on the development of his views as shown in his letters, that in a
third edition Darwin would probably have laid more stress on the influence
of external environment. He himself feels that there are gaps in his
proofs here, and says in self-criticism: "The views here advanced, on the
part which sexual selection has played in the history of man, want
scientific precision." ("Descent of Man", page 924.) I need here only
point out that it is impossible to explain the graduated stages of skin-
colour by sexual selection, since it would have produced races sharply
defined by their colour and not united to other races by transition stages,
and this, it is well known, is not the case. Moreover, the fact
established by me ("Die Hautfarbe des Menschen", "Mitteilungen der
Anthropologischen Gesellschaft in Wien", Vol. XXXIV. pages 331-352.), that
in all races the ventral side of the trunk is paler than the dorsal side,
and the inner surface of the extremities paler than the outer side, cannot
be explained by sexual selection in the Darwinian sense.

With this I conclude my brief survey of the rich contents of Darwin's book.
I may be permitted to conclude by quoting the magnificent final words of
"The Descent of Man": "We must, however, acknowledge, as it seems to me,
that man, with all his noble qualities, with sympathy which feels for the
most debased, with benevolence which extends not only to other men but to
the humblest living creature, with his god-like intellect which has
penetrated into the movements and constitution of the solar system--with
all these exalted powers--Man still bears in his bodily frame the indelible
stamp of his lowly origin." (Ibid. page 947.)

What has been the fate of Darwin's doctrines since his great achievement?
How have they been received and followed up by the scientific and lay
world? And what do the successors of the mighty hero and genius think now
in regard to the origin of the human race?

At the present time we are incomparably more favourably placed than Darwin
was for answering this question of all questions. We have at our command
an incomparably greater wealth of material than he had at his disposal.
And we are more fortunate than he in this respect, that we now know
transition-forms which help to fill up the gap, still great, between the
lowest human races and the highest apes. Let us consider for a little the
more essential additions to our knowledge since the publication of "The
Descent of Man".

Since that time our knowledge of animal embryos has increased enormously.
While Darwin was obliged to content himself with comparing a human embryo
with that of a dog, there are now available the youngest embryos of monkeys
of all possible groups (Orang, Gibbon, Semnopithecus, Macacus), thanks to
Selenka's most successful tour in the East Indies in search of such
material. We can now compare corresponding stages of the lower monkeys and
of the Anthropoid apes with human embryos, and convince ourselves of their
great resemblance to one another, thus strengthening enormously the armour
prepared by Darwin in defence of his view on man's nearest relatives. It
may be said that Selenka's material fils up the blanks in Darwin's array of
proofs in the most satisfactory manner.

The deepening of our knowledge of comparative anatomy also gives us much
surer foundations than those on which Darwin was obliged to build. Just of
late there have been many workers in the domain of the anatomy of apes and
lemurs, and their investigations extend to the most different organs. Our
knowledge of fossil apes and lemurs has also become much wider and more


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