trace of this long and varied ancestry. And it does
retain such traces ; this is a very plain and precise fact.
Haeckel, in his History of Natural Creation, and in
his AntJiropogenie, has well summarized the facts bear-
ing on this question, and it is useless to go over the
details which are familiar to all. In the course of
the few months during which the primitive egg-cell be-
comes evolved into a new-born child, the human organ-
ism offers unmistakable evidence of its animal ancestry



32 EXPERIMENTAL EVOLUTION LECT..



down to the fishes themselves, as, for instance, in its
temporary branchial slits and arches, in the primitive
circulatory apparatus of the earlier stages of develop-
ment, in the various forms which the central nervous
system presents at various periods. The evolution of
the circulatory apparatus is wonderful. At the begin-
ning, during the first hour of evolution, the heart is a
mere tube or bulb, exactly similar to the heart of the
ascidians. Through some modifications, it then pre-
sents the typical aspect of the heart of mud fishes
or Dipnoi'. Later on, we meet with the condition
persistent in adult amphibians ; then follows a stage
which corresponds to that of reptiles, and finally
the heart corresponds to that of birds and mammals.
The same process is to be seen in the evolution of
the principal blood-vessels which are attached to the
central organ of circulation, and the same stages are
successively gone through. Classical as these facts
may be, they may be briefly recalled, as their
signification is of great weight. All fishes, it
is well known, have a number of gill-arches on
each side. In the amphioxus or lancelet, the
lowest of known fish-like forms, there are very
numerous slits, doubtfully homologous with those
of true fishes, which have seven, five, four, or three.
Their use is quite clear : the blood flows through the
arches and the fringes they support, and thus be-



I EMBRYOLOGICAL ARGUMENT 33

comes aerated. If we consider amphibians, we
notice that the gill-arches and corresponding blood-
vessels are retained in the tadpole, and do not wonder
at it, since the tadpole, during its early life, is a gill-
breather. But when we consider reptiles a lizard
for instance we meet with the same vessels. Why ?
No reptile, at any time of its life, is a gill-breather, and
the use of these vessels is not easy to understand. It
cannot be said that they are useful to circulation,
since the circulatory function is much more effective
in birds or mammals, where these vessels are pro-
foundly modified. And no explanation can be given
except that reptiles are derived from amphibians and
fishes, and have retained a large part of the anatomy
of their ancestors. A closer study of the amphibians
shows that this explanation is acceptable. When the
gills shrivel and disappear, while lung respiration be-
comes established, the vessels do not entirely dis-
appear : they remain and persist exactly as before :
the gill-arches minus gills are known as aortic arches.
The need of these aortic arches is gone ; a much better
circulation might be provided otherwise, but this would
require a miracle, and as none occurs, we readily under-
stand how it is that these arches persist ; they have
been useful and necessary, and their presence explains
itself. So, then, if these aortic arches are present in the
reptiles, we must interpret them as we have interpreted

D



34 EXPERIMENTAL EVOLUTION LECT.

those of the frog, as having been useful at some time,
when they were rendered efficient by the presence of
gill-arches and gills, the only difference being in this
last case, that they have been useful not some days or
weeks or months ago, not in the same individual at an
earlier stage of life, but in remote ancestors, and the
remote ancestors are the amphibians, and, further still,
the fishes. If any other intelligible explanation can
be given of the presence of these aortic arches in
reptiles, which never, at any stage of life, are gill-
breathers, we certainly shall listen to it with great at-
tention. But the argument does not stop here, and
things may be pushed further still. Useless as cir-
culatory organs, and useless as respiratory organs,
these aortic arches are not limited to adult amphibians
and reptiles ; we meet them in birds, in mammals, and
even in man himself. At an early stage of their de-
velopment the latter all have on the side of the neck
several gill-slits and aortic arches. Will some creationist
explain why these arches, most of which are destined to
disappear, put in this temporary appearance ? Evolu-
tionists explain it as we have briefly pointed out :
but creationists must explain in some way or other
the temporary presence of these arches of which the
larger part rapidly disappears, while the remainder goes
to build the principal blood-vessels which originate in
the heart.



I EMBRYOLOGICAL ARGUMENT 35

The development of the central nervous system
furnishes us with another important argument out of
many in favour of evolution. The brain of man, dur-
ing the development of the embryo, passes through a
series of stages of increasing complexity, and a careful
study shows that these stages, which are temporary in
the embryo, are permanent in the principal groups of
animals. One may easily detect in the evolution of
the human brain a stage corresponding to that of the
brain of fishes ; but while the fishes permanently re-
tain this brain-structure, an advance occurs in man,
and the brain acquires the characters of the reptilian
encephalon ; later on it progresses again, and acquires
bird characters, then mammalian characters, and
finally it acquires those characters which are peculiar
to mankind. Here again, ontogeny demonstrates phy-
logeny, and phylogeny, that is, derivation from the
lower vertebrate forms, must be admitted to be true,
unless some better explanation can be proposed.

Many other embryological facts do not admit of
any explanation, if the hypothesis of derivation and
descent is not admitted. For instance, on the special
creation theory, why have baleen whales been provided
with a full set of teeth' which remain rudimentary, and
soon disappear in the course of development, and
which are never used nor even could be useful ? Again,
why are there pelvic bones in the whale, and even

D 2



36 EXPERIMENTAL EVOLUTION LECT.

rudiments of the hind-limbs, when both are totally
useless ? Innumerable questions of the same sort
might be and have been asked ; but no satisfactory
answer has yet been given by any creationist.

We may consider as belonging remotely to embry-
ology, some pathological proofs of evolution of which
a passing word may be said. I refer to those many
cases, well known to the pathologist, of tumours, of
fistulae, and of various malformations in many parts
of the body, which are congenital, and are seen in the
child from the moment of his birth, and cannot be
ascribed to any disease or accident. Some of these
cases are most curious and interesting to the evolu-
tionist. A great number of them have been recently
collected in an important work published by Professor
Lannelongue and V. Menard, under the title of
Affections Congenitalesl In the first volume of this
work the only one yet published the authors deal
with the congenital malformations of the head and
neck, and, to those who are not familiar with the evolu-
tionary theory, it may seem astounding that such or
such malformation of the neck or ears is due to the
persistence of the fish or amphibian stage of develop-
ment of these parts. Such is the case, however, and

1 Affections Congenitales, vol. i. Tctc ct Con, Maladies des Bour-
geons de FEmbryon, des Arcs brancliiaux et de leurs Fentes, Paris :
Asselin et Houzeau. 1891.



I PATHOLOGICAL ARGUMENT 37

there is no going against the facts of pathology which
come to furnish an unexpected support to the theory
of evolution. Other pathological, or, at least, abnor-
mal, facts point in the same direction. Some years
ago Dr. L. Testut, of Bordeaux, wrote l a large work
on muscular anomalies in man. It is well known
that there are frequent variations in the muscular
system, muscles being sometimes differently attached,
sometimes absent, while in many cases unusual
muscles appear in the human organism. Have the
persons who offer these abnormal conditions been
specially created with these peculiarities ? There is
no reason for supposing that they originated by a
different method from that with which we are all
acquainted, and then what can the creationists say to
explain these facts ? The evolutionist appeals to
descent, and does not much wonder at the occasional
presence, in man, of muscles which exist permanently
and constantly in other mammals. As Dr. Testut
says, " When we consider the facts separately [the
facts of muscular variation], we find, in short, that
nearly all the muscular anomalies of man are normal
dispositions in organisms which are inferior to him in
the zoological scale." This means that no condition

1 Les Anomalies wuscntaires c/icz F Homme expliquecs par T Anatomic
comparte, by L. Testut, Professor in the Medical School of Bordeaux.
8vo, 850 pages, 1884. Paris : G. Masson.



3cS EXPERIMENTAL EVOLUTION LECT.

is exceptionally met with in man, which does not
represent the normal condition in apes or in other
animals, and this is a fact of great importance to the
evolutionist. But it sorely tries the feelings of the
creationist, who cannot explain the case, who cannot
give any satisfactory reason for the presence, in that
specially created creature, man, of muscles which
typically belong to some other mammal, ape, bear, or
hog, also specially created.

A third argument for evolution is offered by the
facts of morphology. Morphology shows the unity
of plan of quite different organs, as for instance, the
arm of man, the fore-paw of the lion, the wing of the
bat, the fin of the whale, and the wing of the bird ;
it shows that they arc all made up of the same ele-
ments which are more or less modified in each case
according to what is required from them. The same
may be said of the numerous homologous organs in
any large group : as for instance the mouth-parts of
insects, which, although very different in their anatomy
and also in their function, when considered in the dif-
ferent orders of insects, are easily seen to be identical
fundamentally, whether the mouth is used for biting,
for sucking, or for other purposes. Other organs in
the same group, and sometimes in very large sub-
divisions of the animal kingdom, admit of being
morphologically compared, and in many cases we



MORPHOLOGICAL ARGUMENT 39



find that organs which often subserve very different
functions have a common origin, and are identical in
despite of the modifications through which they have
been adapted to their peculiar uses.

Such are, briefly stated, the general proofs of
evolution, or at least the principal among them ; I
must be content with this short statement.

Are these proofs satisfactory, are they convincing,
and what do they demonstrate ?

To an impartial mind, they prove one thing to
begin with, and it is that if we accept the creation
theory, we must believe that creation has been going
on through the whole series of past ages, and that
every type of life has been specially created at some
time or other, being in most, if not all cases, very
similar to types which have lived before, and must
also have been specially created. We must believe
that the Creator while obeying a general tendency to
progress, has first created some types of life which He,
soon after, has diversified in various directions ; and
that some of these types were doubtless of inferior
order, since they have died out, while the types of new
creation, the new species or varieties, have taken their
place. But then, these new species also have proved
inferior, and again new types have been created, or,
again, without proving inferior, they have soon had new
companions more perfect. Upon the whole, innumer-




40 EXPERIMENTAL EVOLUTION LECT.



able creations must have taken place, from the Cam-
brian to the Quaternary period, during millions of
years, and it would seem as if the Creator has been
trying to evolve out of each given type the greatest
number of forms without altering the fundamental
structure of the type Also it would seem as if the
Creator evolved the higher types very slowly and
gradually, through small modifications in various parts,
by a sort of patching, an ever-mending and rearrang-
ing process, just as a man generally proceeds. Things
stand, therefore, exactly as they should stand if the
Creator had been unable to create immediately the
desired form or types ; if He had begun by inferior
forms which required much alteration to attain the
desired degree of efficiency. This inability to attain,
from the first, the desired result, is very striking ;
palaeontology amply illustrates it, and embryology
also ; and to many it may seem surprising, while
evolutionists, and believers in natural selection, do not
wonder at it.

Palaeontology and embryology therefore, while not
disproving the creation theory, render it rather un-
intelligible to our reason, while they display facts
which seem very intelligible upon evolutionary views.
But can palaeontology and embryology, and all the
other facts appealed to by evolutionists, disprove
special creation, and establish the evolution theory



I VALUE OF THESE ARGUMENTS 41

on a firm basis ? Can we consider the doctrine of
the transmutation of species as firmly established, as
demonstrated by fact in an unmistakable manner ?
Certainly not. Evolutionists are convinced of the
truth of their doctrine, they can point to a number of
facts which fit with it, but they cannot give the re-
quired demonstration. The situation of the creation-
ists is different. If they accept the view and they
must do so that every species and variety has been
specially created, they may say that things stand as
they ought to, if special creation has existed ; and as
none of them claim that special creation is going on
now we cannot ask of them to show us a creation of that
sort. On the other hand, evolutionists cannot claim
that evolution is a process of the past. They believe
in its present existence, not only in organic structure,
but in mental organization, and also in the inorganic
world, and they point to the facts of psychology,
zoology, and astronomy, as illustrating the pro-
cess of evolution. And creationists may rightly
demand of them to show precise and unmistakable
instances of transmutation.

Are evolutionists prepared to meet this difficulty,
this requirement ? They may answer that the astron-
omical facts are not under their control, and that an
enormous amount of time is required to yield a single
instance of evolution, so that all they can do is to



42 EXPERIMENTAL EVOLUTION LECT.

note the present condition of things, and let our de-
scendants do the same and draw their conclusions.
So far as psychology is concerned, they may answer
that proofs of individual evolution are to be seen every
day, and that mental evolution is a positive fact in
every individual man, and in the animal kingdom as
a whole. And as concerns zoology, they may reply
that innumerable facts point to descent and evolution.
But the creationists may object to this argument,
and say ; if species are really evolved from each
other and the case of species is only a very small
point in the question you must show us species aris-
ing, by evolution, from former species. In many
palaeontological cases we do not find the connecting
links of which you assume the existence in fact, it
may be said with truth that their existence is not
always* required and, especially, we have not yet
seen a new species originate from a preceding one.
Show us this, show us a positive case of transmuta-
tion through natural means, such as may and do
operate under natural conditions, show us a species
becoming a new one, hitherto unknown? and we
will believe in evolution. Such is the answer of
creationists.

It might be discussed whether this argument is not

1 This requirement is necessary to preclude all objection which might
be raised with reason from the possibility of normal dimorphism.



I A POSITIVE PROOF WANTED. 43

of the most : dangerous sort, more especially for
creationists, whether there are not serious inconveni-
ences in refusing 1 to believe in that which cannot be

o

demonstrated by actual, precise, visible and tangible
fact. But this point had better be left out, and we
will accept the reply of the creationists as it stands.

They ask for a proof of transmutation : we must
secure that proof and meet their demand. How so ?
Through direct experiment, through experimental
transformism. The notion is not exactly a recent
one, but in the present debate it represents the only
line along which we may expect to discover the
positive facts which are necessary. As Buffon has
said, " Man will never be conscious enough of nature's
power, nor of his power on nature." And this state-
ment I believe to be positively true. The only thing
to be clone, at all events, is to subject the notion to
the only possible test of which it admits, and to begin
experiments.

I have just said that the notion is not of recent
origin. The fact is that we find it clearly expressed
in the Nova Atlantis, where Bacon advises experi-
mental investigations for the purpose of discover-
ing how the environment reacts on living organ-
isms and forms species. But the most authorized
defender of experimental transformism has surely
been Isidore Geoffroy Saint Hilaire, and many



44 EXPERIMENTAL EVOLUTION LECT.



passages concerning this matter might be quoted from
his Histoire naturelle generate des Regnes orga-
niques, and his Influence du Monde ambiant, etc. One
will be enough, " Since Nature," he says," left to
herself never allows us to witness considerable modifi-
cations in the conditions of life, it is clear that only
one way is open to us if we wish to perceive such
modifications and to examine their effects on the
organism ; we must oblige Nature to perform that
which she would not spontaneously accomplish."
(Hist. Nat. Gen. iii. p. 389.)

This is exactly what we require. While facts of
observation are sufficiently numerous to give us a fair
idea of the amount of natural variability and variation
although much may yet be done to give an adequate
notion of the amount of this variability we require
to extend our knowledge concerning the causes of vari-
ability (the natural causes, of course), and to discover
in what manner, and to what extent they do operate.
We are already acquainted with some of these causes,
and we know that by selection, crossings, modified en-
vironment, much has been done. But still more can be
done, and in experimental transformism lies the only
test which we can apply to the evolutionary theory. We
must use all the methods we are acquainted with, and
also those, yet unknown, which cannot fail to disclose
themselves when we begin a thorough investigation



I EXPERIMENTAL TEST NECESSARY 45

of the matter, and do our utmost to bring about the
transmutation of any species. We do not specially
desire to transform any one species into another
known at present ; we wish to transform it into a new
species. And this is necessary, if we do not wish to
remain open to an objection suggested by the facts of
dimorphism. Many species occur in two or more forms,
sometimes very different, and if we were merely to
transmute one species into another, it might be said
that we had mistaken the two forms of a dimorphic
species for two different species, and then our attempt
would be useless to a large extent.

Experimental transformism is what we need now,
and therein lies the only method we can use.

But it must be demonstrated that this test is avail-
able, and it remains to show what are the facts which
lie at its basis, and what are the methods to be used.



LECTURE II

Summary Experimental Evolution based on Three Groups of Facts
First Group : the Facts of Natural or Spontaneous Variation :
Organisms are not rigid structures, but exhibit much plasticity.
Facts of Variation in Colour, correlated sometimes, and
perhaps always, with variation of chemical composition
(Armand Gautier's investigations) ; Variation in Dimensions and
Experiments on the real cause of this Variation, .Semper and the
Author ; Variation in Integuments, Form, Shape of Fruits and
Leaves, Flowers Penzig's Pflanzcn-Ter dialogic Skeleton,
Muscles, Internal Organs and Viscera ; Sexuality Camerano's
Neotenia.

TJIUI.I groups of facts lie at the basis of experi-
mental transformism and display at the same time
its conditions and its methods. The first, and most
important, comprises the facts which illustrate varia-
bility in the state of nature, natural or spontaneous
variability. Spontaneous, we call it, but in fact we use
the word only because we are ignorant of the real and
positive causes of this variability. The second group
includes the facts of variation under domestication
and culture ; the third, the facts illustrating the direct
influence of environment as a factor of modification and
transformation. These three groups of facts require



LECT. ii BASIS OF EXPERIMENTAL EVOLUTION 47

to be briefly stated in order to show how experimental
transformism must be carried out. Of course it is of
much importance to prove that living organisms
display a marked tendency to vary, under natural con-
ditions, in most of their parts, in a more or less marked
degree. For this natural variability l is that which

1 Cornevin (Traitc de Zootechnie generate, 1891, p. 226) establishes
the following list of the modes of variation among domestic animals :

I. Morphological variations.

Variations through disappearance. Absence of horns, ears,

hair, pigment, etc.
Total. Dwarfing, discolour-
ation.

arrested ' Partial. Niatism, partial

development, j discolouration, reduction
in the number of limbs,
etc.

juxtaposition. Is seen in some hybrids
when the characters of
both progenitors coexist
side by side.

fusion. Diminished number of

ribs, teeth, digits, verte-
brae, etc.

transformation. Wool replaced -by hair;

scales replaced by fea-
thers, etc.

j Total. Giants, melanism,
; extreme hairiness.

- hypertrophy. Partial Drooping ears ;
very long horns, hairs
or feathers of unusual
length.

( Supplementary vertebrae
division or ribs, teeth, horns, digits,

repetition. /



48 EXPERIMENTAL EVOLUTION LECT.

has allowed natural selection to operate, and allows
us to expect to push things further in the way of
direct experiment.

I do not intend to recall here all the facts which
have been quoted by a large number of naturalists, up
to the present day. I shall merely call attention to
the most important of them, using again preferably,
as they may be less familiar to my hearers, those
which I have been able to collect from French
sources.

One of the variable characters in most living beings
is colour, in most, not in all, for there is among the
human races a strong tendency to the preservation of
the race-colour, while among animals, and especially
plants, colour varies a great deal. And this is the
reason why Linnaeus wrote his ever-quoted nimium

II. Physiological variations.

Variations through diminished activity. Lateness of develop-
ment ; enfeeble -
ment of sexual ten-
dencies ; sluggish-
ness.

earlier Precocity.

exaggerated Increase in fertility,

etc.

stronger Vigour ; immunity

from diseases, etc.

To this list, as I shall show later on, we must make an important
addition in Group II., and add what I propose to call physiological or
chemical variation, although it differs entirely from the sort of variation
included by Cornevin under the same name



COLOUR- VARIATION 49



ne crede color i. It may be noticed here that persons who
want their supposed good sayings to travel far and
long, should always say them in Latin ; if Linnaeus
had written the four words above in good sensible
English, or in clear French, his saying, which seems
to be a sort of divinely inspired axiom for many,
would never have met with the success it has obtained,
and it would have been better. Perhaps the fact that
these words are a quotation from Virgil (Eclogues, ii.
17) has something to do with the matter. Accepting
this dictum, many have considered colour as of no im-
portance in the organism, whereas in many cases it is