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Title: Biology
A lecture delivered at Columbia University in the series
on Science, Philosophy and Art November 20, 1907
Author: Edmund Beecher Wilson
Release Date: July 26, 2006 [EBook #18911]
Language: English
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BIOLOGY
BY
EDMUND BEECHER WILSON
PROFESSOR OF ZOOLOGY
COLUMBIA UNIVERSITY
New York
THE COLUMBIA UNIVERSITY PRESS
1908
BIOLOGY
A LECTURE DELIVERED AT COLUMBIA UNIVERSITY
IN THE SERIES ON SCIENCE, PHILOSOPHY AND ART
NOVEMBER 20, 1907
BIOLOGY
BY
EDMUND BEECHER WILSON
PROFESSOR OF ZOOLOGY
COLUMBIA UNIVERSITY
New York
THE COLUMBIA UNIVERSITY PRESS
1908
COPYRIGHT, 1908,
by THE COLUMBIA UNIVERSITY PRESS.
Set up, and published March, 1908.
BIOLOGY
I must at the outset remark that among the many sciences that are
occupied with the study of the living world there is no one that may
properly lay exclusive claim to the name of Biology. The word does
not, in fact, denote any particular science but is a generic term
applied to a large group of biological sciences all of which alike are
concerned with the phenomena of life. To present in a single address,
even in rudimentary outline, the specific results of these sciences is
obviously an impossible task, and one that I have no intention of
attempting. I shall offer no more than a kind of preface or
introduction to those who will speak after me on the biological
sciences of physiology, botany and zoology; and I shall confine it to
what seem to me the most essential and characteristic of the general
problems towards which all lines of biological inquiry must sooner or
later converge.
It is the general aim of the biological sciences to learn something of
the order of nature in the living world. Perhaps it is not amiss to
remark that the biologist may not hope to solve the ultimate problems
of life any more than the chemist and physicist may hope to penetrate
the final mysteries of existence in the non-living world. What he can
do is to observe, compare and experiment with phenomena, to resolve
more complex phenomena into simpler components, and to this extent, as
he says, to "explain" them; but he knows in advance that his
explanations will never be in the full sense of the word final or
complete. Investigation can do no more than push forward the limits of
knowledge.
The task of the biologist is a double one. His more immediate effort is
to inquire into the nature of the existing organism, to ascertain in
what measure the complex phenomena of life as they now appear are
capable of resolution into simpler factors or components, and to
determine as far as he can what is the relation of these factors to
other natural phenomena. It is often practically convenient to consider
the organism as presenting two different aspects--a structural or
morphological one, and a functional or physiological--and biologists
often call themselves accordingly morphologists or physiologists.
Morphological investigation has in the past largely followed the method
of observation and comparison, physiological investigation that of
experiment; but it is one of the best signs of progress that in recent
years the fact has come clearly into view that morphology and
physiology are really inseparable, and in consequence the distinctions
between them, in respect both to subject matter and to method, have
largely disappeared in a greater community of aim. Morphology and
physiology alike were profoundly transformed by the introduction into
biological studies of the genetic or historical point of view by
Darwin, who did more than any other to establish the fact, suspected by
many earlier naturalists, that existing vital phenomena are the outcome
of a definite process of evolution; and it was he who first fully
brought home to us how defective and one-sided is our view of the
organism so long as we do not consider it as a product of the past. It
is the second and perhaps greater task of the biologist to study the
organism from the historical point of view, considering it as the
product of a continuous process of evolution that has been in operation
since life began. In its widest scope this genetic inquiry involves
not only the evolution of higher forms from lower ones, but also the
still larger question of the primordial relation of living things to
the non-living world. Here is involved the possibility so strikingly
expressed many years ago by Tyndall in that eloquent passage in the
Belfast address, where he declared himself driven by an intellectual
necessity to cross the boundary line of the experimental evidence and
to discern in non-living matter, as he said, the promise and potency of
every form and quality of terrestrial life. This intellectual necessity
was created by a conviction of the continuity and consistency of
natural phenomena, which is almost inseparable from the scientific
attitude towards nature. But Tyndall's words stood after all for a
confession of faith, not for a statement of fact; and they soared far
above the _terra firma_ of the actual evidence. At the present day we
too may find ourselves logically driven to the view that living things
first arose as a product of non-living matter. We must fully recognize
the extraordinary progress that has been made by the chemist in the
artificial synthesis of compounds formerly known only as the direct
products of living protoplasm. But it must also be admitted that we are
still wholly without evidence of the origin of any living thing, at any
period of the earth's history, save from some other living thing; and
after more than two centuries Redi's aphorism _omne vivum e vivo_
retains to-day its full force. It is my impression therefore that the
time has not yet come when hypotheses regarding a different origin of
life can be considered as practically useful.
If I have the temerity to ask your attention to the fundamental
problem towards which all lines of biological inquiry sooner or later
lead us it is not with the delusion that I can contribute anything new
to the prolonged discussions and controversies to which it has given
rise. I desire only to indicate in what way it affects the practical
efforts of biologists to gain a better understanding of the living
organism, whether regarded as a group of existing phenomena or as a
product of the evolutionary process; and I shall speak of it, not in
any abstract or speculative way, but from the standpoint of the
working naturalist. The problem of which I speak is that of organic
mechanism and its relation to that of organic adaptation. How in
general are the phenomena of life related to those of the non-living
world? How far can we profitably employ the hypothesis that the living
body is essentially an automaton or machine, a configuration of
material particles, which, like an engine or a piece of clockwork,
owes its mode of operation to its physical and chemical construction?
It is not open to doubt that the living body _is_ a machine. It is a
complex chemical engine that applies the energy of the food-stuffs to
the performance of the work of life. But is it something more than a
machine? If we may imagine the physico-chemical analysis of the body
to be carried through to the very end, may we expect to find at last
an unknown something that transcends such analysis and is neither a
form of physical energy nor anything given in the physical or chemical
configuration of the body? Shall we find anything corresponding to the
usual popular conception--which was also along the view of
physiologists--that the body is "animated" by a specific "vital
principle," or "vital force," a dominating "archæus" that exists only
in the realm of organic nature? If such a principle exists, then the
mechanistic hypothesis fails and the fundamental problem of biology
becomes a problem _sui generis_.
In its bearing on man's place in nature this question is one of the
most momentous with which natural science has to deal, and it has
occupied the attention of thinking men in every age. I cannot trace
its history, but it will be worth our while to place side by side the
words of three of the great leaders of modern scientific and
philosophic thought. The saying has been attributed to Descartes,
"Give me matter and I will construct the world"--meaning by this the
living world as well as the non-living; but Descartes specifically
excepted the human mind. I do not know whether the great French
philosopher actually used these particular words, but they express the
essence of the mechanistic hypothesis that he adopted. Kant utterly
repudiated such a conception in the following well known passage: "It
is quite certain that we cannot become adequately acquainted with
organized creatures and their hidden potentialities by means of the
merely mechanical principles of nature, much less can we explain them;
and this is so certain that we may boldly assert that it is absurd for
man even to make such an attempt or to hope that a Newton may one day
arise who will make the production of a blade of grass comprehensible
to us according to natural laws that have not been ordered by design.
Such an insight we must absolutely deny to man." Still, in another
place Kant admitted that the facts of comparative anatomy give us "a
ray of hope, however faint, that something may be accomplished by the
aid of the principle of the mechanism of nature, without which there
can be no science in general." It is interesting to turn from this to
the bold and aggressive assertion of Huxley: "Living matter differs
from other matter in degree and not in kind, the microcosm repeats the
macrocosm; and one chain of causation connects the nebulous origin of
suns and planetary systems with the protoplasmic foundations of life
and organization."
Do not expect me to decide where such learned doctors disagree; but I
will at this point venture on one comment which may sound the key-note
of this address. Perhaps we shall find that in the long run and in the
large sense Kant was right; but it is certain that to-day we know
very much more about the formation of the living body, whether a blade
of grass or a man, than did the naturalists of Kant's time; and for
better or for worse the human mind seems to be so constituted that it
will continue its efforts to explain such matters, however difficult
they may seem to be. But I return to our more specific inquiry with
the remark that the history of physiology in the past two hundred
years has been the history of a progressive restriction of the notion
of a "vital force" or "vital principle" within narrower and narrower
limits, until at present it may seem to many physiologists that no
room for it remains within the limits of our biological philosophy.
One after another the vital activities have been shown to be in
greater or less degree explicable or comprehensible considered as
physico-chemical operations of various degrees of complexity. Every
physiologist will maintain that we cannot name one of these
activities, not even thought, that is not carried on by a physical
mechanism. He will maintain further that in most cases the vital
actions are not merely accompanied by physico-chemical operations but
actually consist of them; and he may go so far as definitely to
maintain that we have no evidence that life itself can be regarded as
anything more than their sum total. He is able to bring forward cogent
evidence that all modes of vital activity are carried on by means of
energy that is set free in protoplasm or its products by means of
definite chemical processes collectively known as metabolism. When the
matter is reduced to its lowest terms, life, as thus viewed, seems to
have its root in chemical change; and we can understand how an eminent
German physiologist offers us a definition or characterization of life
that runs: "The life-process consists in the metabolism of proteids."
I ask your particular attention to this definition since I now wish to
contrast with it another and very different one.
I shall introduce it to your attention by asking a very simple
question. We may admit that digestion, for example, is a purely
chemical operation, and one that may be exactly imitated outside the
living body in a glass flask. My question is, how does it come to pass
that an animal has a stomach?--and, pursuing the inquiry, how does it
happen that the human stomach is practically incapable of digesting
cellulose, while the stomachs of some lower animals, such as the goat,
readily digest this substance? The earlier naturalists, such as
Linnaeus, Cuvier or Agassiz, were ready with a reply which seemed so
simple, adequate and final that the plodding modern naturalist cannot
repress a feeling of envy. In their view plants and animals are made
as they were originally created, each according to its kind. The
biologist of to-day views the matter differently; and I shall give his
answer in the form in which I now and then make it to a student who
may chance to ask why an insect has six legs and a spider eight, or
why a yellowbird is yellow and a bluebird blue. The answer is: "For
the same reason that the elephant has a trunk." I trust that a certain
rugged pedagogical virtue in this reply may atone for its lack of
elegance. The elephant has a trunk, as the insect has six legs, for
the reason that such is the specific nature of the animal; and we may
assert with a degree of probability that amounts to practical
certainty that this specific nature is the outcome of a definite
evolutionary process, the nature and causes of which it is our
tremendous task to determine to such extent as we may be able. But
this does not yet touch the most essential side of the problem. What
is most significant is that the clumsy, short-necked elephant has been
endowed--"by nature," as we say--with precisely such an organ, the
trunk, as he needs to compensate for his lack of flexibility and
agility in other respects. If we are asked _why_ the elephant has a
trunk, we must answer because the animal needs it. But does such a
reply in itself explain the fact? Evidently not. The question which
science must seek to answer, is _how_ came the elephant to have a
trunk; and we do not properly answer it by saying that it has
developed in the course of evolution. It has been well said that even
the most complete knowledge of the genealogy of plants and animals
would give us no more than an ancestral portrait-gallery. We must
determine the causes and conditions that have cooperated to produce
this particular result if our answer is to constitute a true
scientific explanation. And evidently he who adopts the machine-theory
as a general interpretation of vital phenomena must make clear to us
how the machine was built before we can admit the validity of his
theory, even in a single case. Our apparently simple question as to
why the animal has a stomach has thus revealed to us the full
magnitude of the task with which the mechanist is confronted; and it
has brought us to that part of our problem that is concerned with the
nature and origin of organic adaptations. Without tarrying to attempt
a definition of adaptation I will only emphasize the fact that many of
the great naturalists, from Aristotle onward, have recognized the
purposeful or design-like quality of vital phenomena as their most
essential and fundamental characteristic. Herbert Spencer defined life
as the continuous _adjustment_ of internal relations to external
relations. It is one of the best that has been given, though I am not
sure that Professor Brooks has not improved upon it when he says that
life is "response to the order of nature." This seems a long way from
the definition of Verworn, heretofore cited, as the "metabolism of
proteids." To this Brooks opposes the telling epigram: "The essence of
life is not protoplasm but purpose."
Without attempting adequately to illustrate the nature of organic
adaptations, I will direct your attention to what seems to me one of
their most striking features regarded from the mechanistic position.
This is the fact that adaptations so often run counter to direct or
obvious mechanical conditions. Nature is crammed with devices to
protect and maintain the organism against the stress of the
environment. Some of these are given in the obvious structure of the
organism, such as the tendrils by means of which the climbing plant
sustains itself against the action of gravity or the winds, the
protective shell of the snail, the protective colors and shapes of
animals, and the like. Any structural feature that is useful because
of its construction is a structural adaptation; and when such
adaptations are given the mechanist has for the most part a relatively
easy task in his interpretation. He has a far more difficult knot to
disentangle in the case of the so-called functional adaptations, where
the organism modifies its activities (and often also its structure) in
response to changed conditions. The nature of these phenomena may be
illustrated by a few examples so chosen as to form a progressive
series. If a spot on the skin be rubbed for some time the first result
is a direct and obviously mechanical one; the skin is worn away. But
if the rubbing be continued long enough, and is not too severe, an
indirect effect is produced that is precisely the opposite of the
initial direct one; the skin is replaced, becomes thicker than before,
and a callus is produced that protects the spot from further injury.
The healing of a wound involves a similar action. Again, remove one
kidney or one lung and the remaining one will in time enlarge to
assume, as far as it is able, the functions of both. If the leg of a
salamander or a lobster be amputated, the wound not only heals but a
new leg is regenerated in place of that which has been lost. If a
flatworm be cut in two, the front piece grows out a new tail, the hind
piece a new head, and two perfect worms result. Finally, it has been
found in certain cases, including animals as highly organized as
salamanders, that if the egg be separated into two parts at an early
period of development each part develops into a perfect embryo animal
of half the usual size, and a pair of twins results. In each of these
cases the astonishing fact is that a mechanical injury sets up in the
organism a complicated adaptive response in the form of operations
which in the end counteract the initial mechanical effect. It is no
doubt true that somewhat similar self-adjustments or responses may be
said to take place in certain non-living mechanical systems, such as
the spinning top or the gyroscope; but those that occur in the living
body are of such general occurrence, of such complexity and variety,
and of so design-like a quality, that they may fairly be regarded as
among the most characteristic of the vital activities. It is precisely
this characteristic of many vital phenomena that renders their
accurate analysis so difficult and complex a task; and it is largely
for this reason that the biological sciences, as a whole, still stand
far behind the physical sciences, both in precision and in
completeness of analysis.
What is the actual working attitude of naturalists towards the general
problem that I have endeavored to outline? It would be a piece of
presumption for me to speak for the body of working biologists, and I
will therefore speak for only one of them. It is my own conviction
that whatever be the difficulties that the mechanistic hypothesis has
to face, it has established itself as the most useful working
hypothesis that we can at present employ. I do not mean to assert that
it is adequate, or even true. I believe only that we should make use
of it as a working program, because the history of biological research
proves it to have been a more effective and fruitful means of
advancing knowledge than the vitalistic hypothesis. We should
therefore continue to employ it for this purpose until it is clearly
shown to be untenable. Whether we must in the end adopt it will
depend on whether it proves the simplest hypothesis in the large
sense, the one most in harmony with our knowledge of nature in
general. If such is the outcome, we shall be bound by a deeply lying
instinct that is almost a law of our intellectual being to accept it,
as we have accepted the Copernican system rather than the Ptolemaic. I
believe I am right in saying that the attitude I have indicated as a
more or less personal one is also that of the body of working
biologists, though there are some conspicuous exceptions.
In endeavoring to illustrate how this question actually affects
research I will offer two illustrative cases, one of which may
indicate the fruitfulness of the mechanistic conception in the
analysis of complex and apparently mysterious phenomena, the other the
nature of the difficulties that have in recent years led to attempts
to re-establish the vitalistic view. The first example is given by the
so-called law or principle of Mendel in heredity. The principle
revealed by Mendel's wonderful discovery is not shown in all the
phenomena of heredity and is probably of more or less limited
application. It possesses however a profound significance because it
gives almost a demonstration that a definite, and perhaps a relatively
simple, mechanism must lie behind the phenomena of heredity in
general. Hereditary characters that conform to this law undergo
combinations, disassociations and recombinations which in certain way
suggest those that take place in chemical reactions; and like the
latter they conform to definite quantitative rules that are capable of
arithmetical formulation. This analogy must not be pressed too far;
for chemical reactions are individually definite and fixed, while
those of the hereditary characters involve a fortuitous element of
such a nature that the numerical result is not fixed or constant in
the individual case but follows the law of probability in the
aggregate of individuals. Nevertheless, it is possible, and has
already become the custom, to designate the hereditary organization by
symbols or formulas that resemble those of the chemist in that they
imply the _quantitative_ results of heredity that follow the union of
compounds of known composition. Quantitative prediction--not precisely
accurate, but in accordance with the law of probability--has thus
become possible to the biological experimenter on heredity. I will
give one example of such a prediction made by Professor Cuénot in
experimenting on the heredity of color in mice (see the following
table). The experiment extended through three generations. Of the four
grandparents three were pure white albinos, identical in outward
appearance, but of different hereditary capacity, while the fourth was
a pure black mouse. The first pair of grandparents consisted of an
albino of gray ancestry, AG, and one of black ancestry, AB. The second
pair consisted of an albino of yellow ancestry, AY, and a black mouse,
CB. The result of the first union, AG x AB is to produce again pure
white mice of the composition AGAB. The second union, AY x CB is to
produce mice that appear pure _yellow_, and have the formula AYCB.
What, now, will be the result of uniting the two forms thus
produced--_i.e._ AGAB × AYCB? Cuénot's prediction was that they should
yield eight different kinds of mice, of which four should be white,
two yellow, one black and one gray. The actual aggregate result of
such unions, repeatedly performed, compared with the theoretic
expectation, is shown in the foregoing table. As will be seen, the
correspondence, though close, is not absolutely exact, yet is near
enough to prove the validity of the principle on which the prediction
was based, and we may be certain that had a much larger number of
these mice been reared the correspondence would have been still
closer. I have purposely selected a somewhat complicated example, and
time will not admit of a full explanation of the manner in which this
particular result was reached. I will however attempt to give an
indication of the general Mendelian principle by means of which
predictions of this kind are made. This principle appears in its
simplest form in the behavior of two contrasting characters of the
same general type--for instance two colors, such as gray and white in
mice. If two animals, which show respectively two such characters are
bred together, only one of the characters (known as the "dominant")
appears in the offspring, while the other (known as the "recessive")
disappears from view. In the next generation, obtained by breeding
these hybrids together, both characters appear separately and in a
definite ratio, there being in the long run three individuals that
show the dominant character to one that shows the recessive. Thus, in
the case of gray and white mice, the first cross is always gray, while
the next generation includes three grays to one white. This is the
fundamental Mendelian ratio for a single pair of characters; and from
it may readily be deduced the more complicated combinations that
appear when two or more pairs of characters are considered together.
Such combinations appear in definite series, the nature of which may
be worked out by a simple method of binomial expansion. By the use of
this principle astonishingly accurate numerical predictions may be
made, even of rather complex combinations; and furthermore, new
combinations may be, and have been, artificially produced, the number,
character and hereditary capacity of which are known in advance. The
fundamental ratio for a single pair of characters is explained by a
very simple assumption. When a dominant and a recessive character are
associated in a hybrid, the two must undergo in some sense a
disjunction or separation in the formation of the germ-cells of the
hybrid. This takes place in a quite definite way, exactly half the
germ-cells in each sex receiving the potentiality of the dominant
character, the other half the potentiality of the recessive. This is
roughly expressed by saying that the germ-cells are no longer hybrid,
like the body in which they arise, but bear one character or the
other; and although in a technical sense this is probably not
precisely accurate, it will sufficiently answer our purpose. If, now,
it be assumed that fertilization takes place fortuitously--that is
that union is equally probable between germ-cells bearing the same
character and those bearing opposite characters,--the observed
numerical ratio in the following generation follows according to the
law of probability. Thus is explained both the fortuitous element that
differentiates these cases from exact chemical combinations, and the
definite numerical relations that appear in the aggregate of
individuals.
Grandparents AG (white) AB (white) AY (white) CB (black)
| | | |
+---------+ +-----------+
| |
Parents AGAB (white) AYCB (yellow)
| |
+----------------------+
| Observed Calculated
{AGAY}
{ABAY} (White) 81 76
{AGAB}
Offspring ---------------{ABAB}
{
{AGCY} (Yellow) 34 38
{ABCY}
{
{ABCB (Black) 20 19
{AGCB (Gray) 16 19
---- ----
151 152
Now, the point that I desire to emphasize is that one or two very
simple mechanistic assumptions give a luminously clear explanation of
the behavior of the hereditary characters according to Mendel's law,
and at one stroke bring order out of the chaos in which facts of this
kind at first sight seem to be. Not less significant is the fact that
direct microscopical investigation is actually revealing in the
germ-cells a physical mechanism that seems adequate to explain the
disjunction of characters on which Mendel's law depends; and this
mechanism probably gives us also at least a key to the long standing
riddle of the determination and heredity of sex. These phenomena are
therefore becoming intelligible from the mechanistic point of view.
From any other they appear as an insoluble enigma. When such progress
as this is being made, have we not a right to believe that we are
employing a useful working hypothesis?
But let us now turn to a second example that will illustrate a class
of phenomena which have thus far almost wholly eluded all attempts to
explain them. The one that I select is at present one of the most
enigmatical cases known, namely, the regeneration of the lens of the
eye in the tadpoles of salamanders. If the lens be removed from the
eye of a young tadpole, the animal proceeds to manufacture a new one
to take its place, and the eye becomes as perfect as before. That such
a process should take place at all is remarkable enough; but from a
technical point of view this is not the extraordinary feature of the
case. What fills the embryologist with astonishment is the fact that
the new lens is not formed in the same way or from the same material
as the old one. In the normal development of the tadpole from the egg,
as in all other vertebrate animals, the lens is formed from the outer
skin or ectoderm of the head. In the replacement of the lens after
removal it arises from the cells of the iris, which form the edge of
the optic cup, and this originates in the embryo not from the outer
skin but as an outgrowth from the brain. As far as we can see, neither
the animal itself nor any of its ancestors can have had experience of
such a process. How, then, can such a power have been acquired, and
how does it inhere in the structure of the organism? If the process of
repair be due to some kind of intelligent action, as some naturalists
have supposed, why should not the higher animals and man possess a
similar useful capacity? To these questions biology can at present
give no reply. In the face of such a case the mechanist must simply
confess himself for the time being brought to a standstill; and there
are some able naturalists who have in recent years argued that by the
very nature of the case such phenomena are incapable of a rational
explanation along the lines of a physico-chemical or mechanistic
analysis. These writers have urged, accordingly, that we must
postulate in the living organism some form of controlling or
regulating agency which does not lie in its physico-chemical
configuration and is not a form of physical energy--something that may
be akin to a form of intelligence (conscious or unconscious), and to
which the physical energies are in some fashion subject. To this
supposed factor in the vital processes have been applied such terms as
the "entelechy" (from Aristotle), or the "psychoid"; and some writers
have even employed the word "soul" in this sense--though this
technical and limited use of the word should not be confounded with
the more usual and general one with which we are familiar. Views of
this kind represent a return, in some measure, to earlier vitalistic
conceptions, but differ from the latter in that they are an outcome of
definite and exact experimental work. They are therefore often spoken
of collectively as "neo-vitalism."
It is not my purpose to enter upon a detailed critique of this
doctrine. To me it seems not to be science, but either a kind of
metaphysics or an act of faith. I must own to complete inability to
see how our scientific understanding of the matter is in any way
advanced by applying such names as "entelechy" or "psychoid" to the
unknown factors of the vital activities. They are words that have been
written into certain spaces that are otherwise blank in our record of
knowledge, and as far as I can see no more than this. It is my
impression that we shall do better as investigators of natural
phenomena frankly to admit that they stand for matters that we do not
yet understand, and continue our efforts to make them known. And have
we any other way of doing this than by observation, experiment,
comparison and the resolution of more complex phenomena into simpler
components? I say again, with all possible emphasis, that the
mechanistic hypothesis or machine-theory of living beings is not fully
established, that it _may_ not be adequate or even true; yet I can
only believe that until every other possibility has realty been
exhausted scientific biologists should hold fast to the working
program that has created the sciences of biology. The vitalistic
hypothesis may be held, and is held, as a matter of faith; but we
cannot call it science without misuse of the word.
When we turn, finally, to the genetic or historical part of our task,
we find ourselves confronted with precisely the same general problem
as in case of the existing organism. Biological investigators have
long since ceased to regard the fact of organic evolution as open to
serious discussion. The transmutation of species is not an hypothesis
or assumption, it is a fact accurately observed in our laboratories;
and the theory of evolution is only questioned in the same very
general way in which all the great generalizations of science are held
open to modification as knowledge advances. But it is a very large
question what has caused and determined evolution. Here, too, the
fundamental problem is, how far the process may be mechanically
explicable or comprehensible, how far it is susceptible of formulation
in physico-chemical or mechanistic terms. The most essential part of
this problem relates to the origin of organic adaptations, the
production of the fit. With Kant, Cuvier and Linnaeus believed this
problem scientifically insoluble. Lamarck attempted to find a solution
in his theory of the inheritance of the effects of use, disuse and
other "acquired characters"; but his theory was insecurely based and
also begged the question, since the power of adaptation through which
use, disuse and the like produce their effects is precisely that which
must be explained. Darwin believed he had found a partial solution in
his theory of natural selection, and he was hailed by Haeckel as the
biological Newton who had set at naught the _obiter dictum_ of Kant.
But Darwin himself did not consider natural selection as an adequate
explanation, since he called to its aid the subsidiary hypotheses of
sexual selection and the inheritance of acquired characters. If I
correctly judge, the first of these hypotheses must be considered as
of limited application if it is not seriously discredited, while the
second can at best receive the Scotch verdict, not proven. In any
case, natural selection must fight its own battles.
Latter day biologists have come to see clearly that the inadequacy of
natural selection lies in its failure to explain the origin of the
fit; and Darwin himself recognized clearly enough that it is not an
originative or creative principle. It is only a condition of survival,
and hence a condition of progress. But whether we conceive with Darwin
that selection has acted mainly upon slight individual variations, or
with DeVries that it has operated with larger and more stable
mutations, any adequate general theory of evolution must explain the
origin of the fit. Now, under the theory of natural selection, pure
and simple, adaptation or fitness has a merely casual or accidental
character. In itself the fit has no more significance than the unfit.
It is only one out of many possibilities of change, and evolution by
natural selection resolves itself into a series of lucky accidents.
For Agassiz or Cuvier the fit is that which was designed to fit. For
natural selection, pure and simple, the fit is that which happens to
fit. I, for one, am unable to find a logical flaw in this conception
of the fit; and perhaps we may be forced to accept it as sufficient.
But I believe that naturalists do not yet rest content with it. Darwin
himself was repeatedly brought to a standstill, not merely by specific
difficulties in the application of his theory, but also by a certain
instinctive or temperamental dissatisfaction with such a general
conclusion as the one I have indicated; and many able naturalists feel
the same difficulty to-day. Whether this be justified or not, it is
undoubtedly the fact that few working naturalists feel convinced that
the problem of organic evolution has been fully solved. One of the
questions with which research is seriously engaged is whether
variations or mutations are indeterminate, as Darwin on the whole
believed, or whether they may be in greater or less degree
determinate, proceeding along definite lines as if impelled by a _vis
a tergo_. The theory of "orthogenesis," proposed by Naegeli and Eimer,
makes the latter assumption; and it has found a considerable number of
adherents among recent biological investigators, including some of our
own colleagues, who have made important contributions to the
investigation of this fundamental question. It is too soon to venture
a prediction as to the ultimate result. That evolution has been
orthogenetic in the case of certain groups, seems to be well
established, but many difficulties stand in the way of its acceptance
as a general principle of explanation. The uncertainty that still
hangs over this question and that of the heredity of acquired
characters bears witness to the unsettled state of opinion regarding
the whole problem, and to the inadequacy of the attempts thus far made
to find its consistent and adequate solution.
Here, too, accordingly, we find ourselves confronted with wide gaps in
our knowledge which open the way to vitalistic or transcendental
theories of development. I think we should resist the temptation to
seek such refuge. It is more than probable that there are factors of
evolution still unknown. We can but seek for them. Nothing is more
certain than that life and the evolution of life are natural
phenomena. We must approach them, and as far as I can see must attempt
to analyze them, by the same methods that are employed in the study of
other natural phenomena. The student of nature can do no more than
strive towards the truth. When he does not find the whole truth there
is but one gospel for his salvation--still to strive towards the
truth. He knows that each forward step on the highway of discovery
will bring to view a new horizon of regions still unknown. It will be
an ill day for science when it can find no more fields to conquer. And
so, if you ask whether I look to a day when we shall know the whole
truth in regard to organic mechanism and organic evolution, I answer:
No! But let us go forward.
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BOTANY, by Herbert Maule Richards, _Professor of Botany_.
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SOCIOLOGY, by Franklin Henry Giddings, _Professor of Sociology_.
PHILOSOPHY, by Nicholas Murray Butler. _President of the
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PSYCHOLOGY, by Robert S. Woodworth, _Adjunct Professor of
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METAPHYSICS, by Frederick J.E. Woodbridge, _Johnsonian Professor
of Philosophy_.
ETHICS, by John Dewey, _Professor of Philosophy_.
PHILOLOGY, by A.V.W. Jackson, _Professor of Indo-Iranian
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