Chapter VI: Introduction: §1 (4)

By undertaking the analysis of the characteristics of conscious behaviour without departing from the methods of the traditional physiology of reflex action, biological science in our generation has shown that there is no nicely defined boundary at which physiology ends and moral philosophy begins. Hitherto physiology and academic philosophy have developed independently, because physiologists themselves have accepted the common sense dualism of mind and matter. Moral philosophy can no longer claim that there is any distinctive aspect of the Nature of Life, which lies beyond the province of physiological enquiry. If any fundamental distinction between mind and matter remains, that distinction henceforth defines the antinomy of a _public world_ of common beliefs which all can share, the conceptual world of science in which ethical neutrality and economy of hypothesis reign supreme, and, in contradistinction to that public world, many _private_ worlds which for the present remain impenetrable through the medium of discourse. Biological science is continually socializing our beliefs. What seems irrevocably part of the private worlds of one generation becomes irrevocably part of the public world of its grandchildren. Thus the new pluralism will not be, like the Cartesian system, static, but dynamic. It is ever tending towards a monistic outlook as a limiting case. Such a monism, unlike traditional materialism and traditional idealism will be regarded not as a formula but as an asymptote. It is evidently immaterial to _public_ discourse whether we _privately_ entertain the view that _the_ public world is more or less _real_ than _our_ private worlds. It would thus seem that as biological science invades the province of human behaviour the concept of _publicity_, as I venture to call the communicability of beliefs, will come to occupy the status of importance which _reality_ has held in the systems of egocentric philosophers.

The public world, as I have conceived it, is a construction based on the continuous extension of the principle of mechanism. The principle of mechanism, that a complex system is interpretable only by reference to the properties of its constituent parts, is not urged in the spirit of dogmatic assertion, but because it has served us well in the past. We still await any single verifiable conclusion that is uniquely developed from any alternative principle. Holism, the newest form of Vitalism, claims to have found an alternative or supplementary principle that is essentially teleological. The holist does not specify by reference to any single concrete situation how he proposes to use his principle. It is admitted even by the mechanist that we are not in a position to construct a symbolic relation which will completely describe the vagaries of a Ford car in terms of the field equations of the proton and electron. Does the holist wish us to believe that we can help anyone to drive a car by assuring him that at every level of complexity between the internal structure of the atom and the newly licensed automobile there emerges an ever-increasing urge to a wholeness or unity which is somehow indefinably different from the interaction of the parts? Verily the mechanist of all people knows that we know in part and we prophesy in part. For this very reason, because he is prepared to await with patience the slow advance of science, he refuses to subscribe to high-sounding pseudonyms for ignorance and principles that are never seriously intended to be put into practice.

In the recent symposium on _The Nature of Life_ before the British Association both General Smuts in his exposition of the holistic standpoint and Dr. Haldane who supported him dwelt upon the supposed collapse of mechanistic principles in physics itself. The former cited in support of his point a somewhat rhetorical remark by Dr. Whitehead in this sense. It is of course evident that if our mechanical principles undergo modification our biological interpretations must share in the general change of outlook. It is, therefore, beside the point to criticize the mechanistic standpoint on the ground that our mechanical principles are undergoing revision. Let us examine this objection a little more closely. Experimental biology, we are told, has been directed towards the attempt to describe the properties of living matter in terms of the traditional physical concepts of mass, length, time, energy, etc. Since these concepts now appear to be less fundamental than we once believed, the hope that a complete mathematical description of the universe is realizable, has, as Mr. Sullivan asserts with triumphant _naïveté_, “no longer any plausibility.” Surely it is evident that a signal advance towards a more monistic interpretation of nature has been made, when the analysis of any biological phenomenon has been achieved with the aid of traditional physical concepts, and when concepts once peculiar to biology, as affinity was once peculiar to chemistry, have been translated into the traditional language of physics. Physics to-day is seeking a new synthesis to take into one system of equations all the old data, and many new ones which have lately accumulated. This is not a new situation. The old mechanics remains as valid as ever for the realm in which it was developed to operate. To effect a more comprehensive scheme it has been necessary to examine many of the old postulates. In the meantime we have to recognize that we are not so near to a single unifying hypothesis as the rise of energetics led the physicists of Kelvin’s generation to hope. What does this signify? Certainly not that mechanics has abandoned the principles of mechanism. Is it not rather a fact that the modern physicist is complaining that the inadequacy of Newtonian principles is in part attributable to teleological implications insufficiently recognized till now? The very hope of finality which Kelvin’s generation entertained seems from the new mechanistic standpoint, as I have stated it, to savour of scholasticism.

In taking this line General Smuts and Dr. Haldane seem to me to have laid bare the source of a misunderstanding that lies at the root of most of the criticism which vitalists old or new direct against the new or the old mechanistic standpoint. Those who have the scholastic predilection for finality and the scholastic predilection for the abstract noun, do not seem to be able to believe in the existence of people who are not like themselves. They cannot, it appears, understand that unless one starts off with the obsession that the universe can be summed up in a monosyllable, one is under no imperative necessity on the one hand to be resentful towards or disappointed with science because it lays no claim to the finality of religious dogma, nor on the other to make the assumption that such finality ought to be obtainable. The mechanist does not claim that his system is, or ever will be, complete in the sense that science will one day find an answer for all the conundrums which the scholastic temperament dictates. On the contrary, it is the essence of the mechanistic position that there is a technique of asking questions profitably as well as a way of answering them satisfactorily. All the mechanist claims is that as far as we can see at present his way of dealing with things leads to the most complete unanimity which it is possible to attain. Against the old vitalism, that of Dr. Haldane, who denies that the principle of mechanism can ever deal with conscious behaviour the older mechanistic outlook was secure in the assurance that, if the principle of mechanism failed at such a level, no other principle led to verifiable predictions in the same field. Against the new vitalism or holistic standpoint of General Smuts which no longer asserts dogmatically that the principle of mechanism is inapplicable at any specific level of existence, but contends that it does not anywhere give a complete account, the new mechanistic or _publicist_ standpoint which I have outlined contends that if the principle of mechanism fails to give a complete account at any level no alternative or supplementary principle has been discovered. The reply of the mechanist old or new to the vitalist old or new is that of Mr. W. B. Yeats’ faeries:

“Is anything better, anything better
Tell us it then...”

It follows that, in any discussion between the two, the combatants are generally at cross-purposes. The mechanist is primarily concerned with an epistemological issue. His critic has always an ontological axe to grind. The mechanist is concerned with how to proceed to a construction which will represent as much about the universe as human beings with their limited range of receptor organs can agree to accept. The vitalist or holist has an incorrigible urge to get behind the limitations of our receptor organs and discover what the universe is _really_ like. What we mean by _really_ in this connexion evidently depends upon whether we view the question socially or individually. In our relation to other human beings the nearest approach to what the universe is really like is found in the schematization of our common experiences. If there is any other reality its sanction is non-social. Thus in contradistinction to the _reality_ of traditional philosophy which is an individualistic concept, the concept of _publicity_, which it is proposed to substitute as the goal of synthetic philosophy, is an essentially social one.

IV. THE CONCEPT OF ADAPTATION

“No philosopher who is rational and modest has ever pretended to
assign the ultimate cause of any natural operation, or to show
distinctly the action of that power which produces single effect
in the universe. It is confessed that the utmost effort of human
reason is to reduce the principles productive of natural phenomena
to a greater simplicity.... The most perfect philosophy of the
natural kind only staves off our ignorance a little longer, as
perhaps the most perfect philosophy of the moral or metaphysical
kind serves only to discover larger portions of it.”--David Hume,
_Sceptical Doubts_

§1

By those who hesitate to commit themselves to an explicit advocacy of either the vitalistic or mechanistic views about the Nature of Life it has often been urged that the concept of adaptation is fundamental to biological science. Professor A. V. Hill is perhaps the most brilliant physiologist now living. He adopts a hopeful attitude to the progress which awaits further analysis of the properties of living matter in physico-chemical terms. He also thinks that, however far mechanistic principles are extended, the biologist will always encounter “adaptation” in the phenomena which he studies. Another distinguished physiologist, Professor Lovatt Evans has expressed himself in rather more emphatic terms.

“Physiologists,” he states, “in attempting to know what life is,
have in my opinion attempted too much, and I think that a new point
of view is essential.... The idea of adaptation, urged by Claude
Bernard, should be adopted by physiology as its basal principle, as
the chemist accepts the conservation of matter or the physicist
the conservation of energy. We need not seek to know why it is so,
that is the province of the philosopher.... It is not a definition
of what life is, but a brief statement of its way.... Life is
conserved by adaptation.”

When I first read these words I was not sure that I agreed with them. I was not quite certain that I knew what they meant. I had already come to the conclusion that the word adaptation is frequently used by biologists without a very clear agreement as to its content. I cannot subscribe to the view that there is a sort of trade union of philosophers to which physiologists are ineligible, unless they can show their articles of apprenticeship. Nor can I conceive what is meant by a concept of life except such as is implied in a statement of _its way_. A scientific concept defines a class of properties. A scientific concept of life or adaptation must conform to this requirement. In this essay my object is not to criticize Professor Lovatt Evans for whose breadth of view I entertain a very sincere respect. I have quoted his words, because they focus attention on some significant and controversial issues. They serve to reveal how imperative it has become that biologists should agree about the sense in which they intend to use the word _adaptation_.

The quotation given above might be interpreted to mean two very different things. If the term adaptation is used to define certain very general characteristics of living systems, it becomes almost co-extensive with a scientific concept of life itself. If we use _principle_ in a somewhat archaic sense to indicate a field for investigation, like the principle of affinity or the active principle of the thyroid gland, there can be no question that the idea of adaptation is the basic principle of physiology. The comparison of the biologist with the chemist or physicist seems to go beyond this, and imply that adaptation is not something to be explored and interpreted, but part of the logical procedure of biology, something by the aid of which we can predict conclusions of universal validity in the field of biological enquiry. I do not think that Professor Lovatt Evans really means this. I do urge that biologists continually confuse within the compass of the concept of adaptation the notion of a problem for solution and of a _vera causa_. This in everything but verbiage is precisely what the cruder type of vitalist does, when he invokes the vital principle. He first introduces a term to describe a large number of things about which we are ignorant and wish that we knew more. He then falls into the trap of imagining that the invention of a new term has solved the problem.

Quite apart from this difference which, if it is to define the scope of our scientific enquiries, cannot be dismissed as metaphysics, biologists differ a good deal concerning the extent of the phenomena and the kinds of phenomena they are dealing with, when they speak of adaptation. The physiologist--in the restricted sense of the term--is usually referring to something which might be called the self-regulating characteristic of the body. The evolutionary biologist--who to-day is a physiologist in the broader sense of the term--is usually thinking of “a change in the structure, and by implication also in the habits of an animal which render it better fitted” for life. I here quote Professor D. M. S. Watson’s suggestive address on adaptation from the evolutionary standpoint.[3] Sometimes the word adaptation has a more comprehensive significance and includes both definitions which I have distinguished. It then amounts to saying that living systems are self-regulating and self-propagating, which is one way of defining the nature of life as a scientific concept. None of these technical uses of the word adaptation imply anything that the most dogmatic mechanist could decry. If we define adaptation as the self-regulating processes by which living matter retains its recognizable characteristics, it is a truism to say that life is preserved by adaptation. In that case, if adaptation is to be made the paramount issue for biological enquiry, we can hardly upbraid our predecessors for presumptuously seeking to know what life is. If we are to reach any agreement about the use of the word adaptation we must therefore retrace our steps, and examine more closely what are the characteristics of a living system. It is useless to define the goal of biological enquiry in terms of a concept which is as vague as life itself. I suggest that when, in its various uses, the term adaptation has any objective utility, it refers to these two more or less distinct categories of characteristics which living beings display, i.e. self-regulating and self-propagating. They are separable issues inasmuch as a worker bee and a Dominican friar are self-regulating but not self-propagating systems. There is no particular reason to object to the use of the prefix, so long as no personalistic implications of the word self are imposed upon it without further discussion.

§2

Of the two ways in which the word adaptation is used in biological discussion, that which implies the notion of self-regulation is most fundamental. A living organism is an extremely complex system in dynamic equilibrium with its environment. The idea of dynamical equilibrium is not peculiar to biology. The atom, which for traditional chemistry was a statical concept, is no longer regarded in that way by the modern physicist. What is more peculiar about living matter is its amazing complexity, and the idea of adaptation in the sense of self-regulation calls attention to the fact that a system of such extreme complexity, a system with so many characteristics, continues to maintain its individuality, i.e., its manifold characteristics, in spite of all the changes that are taking place within it and without. The recognition of this complexity is common ground. If the mechanist underrates the difficulty of the problem, he is certainly to be discouraged, except in so far as the scientist in attacking any problem must always focus his attention on a limited range of data and rule out certain things as insignificant for his present purpose. It may be true, as Professor Lovatt Evans opines, that mechanistic interpretations tend to become arrogant and superficial. Is he on surer ground in holding that “it is unthinkable that a chance encounter of physico-chemical phenomena can be the explanation”? Might we not reflect with David Hume that “our own mind being narrow and contracted, we cannot extend our conception to the variety and extent of nature, but imagine that she is as much bounded in her operations, as we are in our speculation”?

Scientific hypotheses are not always thinkable, if by that we mean pleasant, easy or conformable to common sense. Our grandfathers thought it “inconceivable” that her Gracious Majesty, Queen of Great Britain and Ireland, Empress of India and Defender of the Faith, could be descended from an ape. The atomic structure of matter was unthinkable to many people little more than a century ago. To-day the quantum atomic model is unthinkable; but we think it is the best way of interpreting the data. Given this amazingly complex system in dynamically stable equilibrium with its environment, we have to decide consistently with the fullest requirements of the problems what is the most economical way in which we can envisage its existence. Seeing that a mechanistic interpretation is evidently the most economical one, the real issue is to decide whether there are any characteristics of the complex which are inconsistent with such an attitude.

From the modern standpoint the individuality of the atom is a statistical concept. The atom is in dynamically stable equilibrium with its surroundings. It might, therefore, be argued that a Ford car is an example of a complex mechanism which is in dynamical equilibrium with its environment. This would be a superficial analogy for the order of complexity which we encounter in living matter. The molecular constitution of the parts of a Ford car is comparatively static. In the minutest parts of an organism new molecules are being built up and replacing others that have been broken down. Nevertheless, in all this astonishing panorama of microscopic revolutions which underlie the microscopic continuity of the organism we know of no events which are in conflict with the great generalizations of physical science.

On this point Professor Hill speaks with special authority, when he declares:

“Fortunately for physiology several of the generalizations of
science appear to be fairly strictly true, even when applied
to the living organism. Although such exact experiments are
not possible on man, or animals, or plants, as may be made on
non-living objects, there is little evidence--indeed, I would be
bold and say there is no evidence--that such living creatures can,
in any manner or degree, evade the ordinary laws of mechanics,
chemistry and physics, the principles of the Conservation of Energy
and Mass.... There really is _no_ evidence that momentum and
kinetic energy, that chemical transformations, that electrical and
magnetic phenomena, occur in the living body in any manner, or to
any extent, which differs from that obtaining in the more readily
investigated non-living world.”

In the same lecture Professor Hill replies to a statement which has been frequently reiterated by vitalistic writers including General Smuts and Professor Julian Huxley. Referring to the Second Law of Thermodynamics, he says:

“Philosophically speaking, the Second Law of Thermodynamics,
dealing with the limitations of the availability of Energy, is
more liable to doubt. It is known to rest on a statistical basis,
and when we are dealing with units, complete, self-producing,
yet as invisible and intangible as the filter-passing or other
micro-organisms, it is, theoretically speaking, possible that some
means may be available of evading the statistical relations which
govern the behaviour of larger systems. But here again we must ask
for evidence--and there is none of a precise or definite character
which suggests, in the least degree, that the living cell can
escape the jurisdiction of the Second Law.”

We are thus forced to consider the order of complexity of the living system maintained in dynamical equilibrium with its surroundings as the essential feature which distinguishes it from non-living things. This complexity can be arbitrarily divided into many levels; but for convenience we may confine ourselves to two, the macroscopic and the microscopic. Let us be explicit about the meaning of this distinction. In the more familiar animals, we are accustomed to recognize a variety of responses to a variety of external agencies. Generally speaking in the more complex animals each kind of reactivity and each kind of receptivity is spatially localized. For instance, light impinging upon the retina evokes contraction of the pigment cells in the toes of a frog. From this macroscopic complexity of the gross architecture of the animal body arise two types of problems: first, the problems of co-ordination dealing with the way in which a disturbance recurring in some receptive area is propagated to an effector organ (gland, muscle, etc.) in some other region; and second, the problems of metabolic exchange, dealing with how the supply and distribution of sources of energy for all this display of activity is maintained. The first involves the study of the nervous impulse along the peripheral nerve fibres and through the central nervous system; it also involves the study of the internal secretions. The second involves the study of digestion and assimilation of foodstuffs, the intake of oxygen to burn up the waste products of chemical activity, and the removal of carbon dioxide, water and other products of oxidation. In contradistinction to the gross complexity of organs or populations of cells, we have to take into account the microscopic complexity of the cell itself. This presents a more general issue, because there exist many organisms whose complexity is of the same order as that of the separate cells which make up the bodies of familiar animals of visible dimensions. Two of the major problems of cell physiology concern the way in which the cell maintains its semi-permeability, and the way in which it maintains a constant renewal of chemical materials by utilizing the energy liberated in certain organic oxidations.

If we remove the magneto from a car, we can keep it intact for an indefinite period: it is fundamental to our idea of a mechanism that it can be taken to pieces and put together again. We are so accustomed to think of a leg or an arm as dependent for their activity on the rest of the body, that the conception of a living mechanism is repugnant to common sense. In the laboratory it is possible to study properties of nerve, muscle, the cell membrane, absorption of food in the gut, oxidation of nitrogenous materials in the liver, etc., as isolated events. A person who is not a biologist almost invariably expresses bewilderment when he sees the isolated heart of an animal beating regularly in a perfusion apparatus. There exists the idea that the living organism differs from a mechanical system in that the parts cannot persist without the whole.[4] Behind this illusion of common sense the holistic concept of adaptation stands securely entrenched. The holistic conception implies that for living systems the part must be interpreted in relation to the whole, and not the whole from the interaction of parts. We have seen that the ultimate non-biological constituents of living matter, molecules, atoms, etc., do not behave differently when united to form a living system. In transcending this level of organization we are faced with an equally striking conclusion. The contraction of an isolated muscle preparation is essentially the same as the contraction of a muscle considered as an isolated aspect of the behaviour of the intact organism. The passage of the nervous impulse along an isolated nerve is not fundamentally different from the passage of the nervous impulse in the normal animal. The conversion of sugar into alcohol by the isolated enzyme zymase obtained from crushed yeast cells is a process like that of the conversion of sugar into alcohol by the living yeast fungus. The whole development of physiology, from the time when Haller first made an isolated muscle preparation and Spallanzani produced animal light by moistening a dessicated powder of luminescent jelly fishes, bears witness to the conclusion that the separated constituents of a living whole do not at any level of complexity behave differently from the way in which they behave as parts of a more complex order. Thus, when the fullest recognition is given to the extreme complexity of living systems, the problem of self-regulation submitted to experimental analysis does not bring forward any confirmation for the holistic view of adaptation as the creative interpolation of new irreducible properties at different levels of complexity. The holist may reply that it is one thing to take the living machine to pieces, and another thing to put it together again. Even here the analogy with the machine holds good. To graft the eye of one salamander tadpole on to the head of another individual is now a commonplace of experimental embryology. Five-legged and two-headed newts are now manufactured in the laboratory.

Self-regulation, the way in which an organism maintains a seeming continuity of arrangement in spite of the uninterrupted and ubiquitous flux of macroscopic and microscopic changes which its existence implies, defines the sense in which the term adaptation is ordinarily used by the physiologist. In contradistinction to this physiological and individual use, adaptation is employed in biological discussion in a morphological and specific sense, when we consider how one animal comes to be distinguished from another by some architectural arrangement appropriate to a particular kind of environment. In this sense the problem of adaptation has played a prominent part in the evolutionary speculations of the past century. Given the fact that organisms are not only self-regulating but self-propagating, the evolutionary theory sets out to explain how living systems come to exist in so many specific forms, and how it is that these specific forms are on the whole _fitted_ or _adapted_ to their respective surroundings. The qualification _on the whole_ is highly significant. Organisms display many peculiarities of architecture which by no stretch of imagination can be regarded as necessarily fitting them better for their conditions of life. To assume that every peculiarity of structure in an animal is useful to it in the struggle for existence is a pure assumption unfounded on anything but teleological prejudice.

Adaptation in the morphological sense really includes two ideas which to some extent coalesce, and are therefore all the more readily confused. At times the word implies nothing more than _viability_. In this sense adaptation is the whole problem of evolution. Up to a certain point an organism must be “suited” to its environment in order to live at all. At other times adaptation is extended to mean an essential utility in every detail of the structure of an organism. This is a mischievous implication which, as will be seen later, has hindered the formation of a clear conception of the evolutionary process. Even if we could justify the belief that female peafowl are as much impressed by peacocks as are some male biologists, we have still failed to supply a criterion of survival value which has any satisfactory significance. The enthusiast who describes an adaptation is often like the advertizing manager who tells us how many customers we shall get, if we advertize with him, but is inclined to be reticent about whether the profit derived from more customers is commensurate with the fees he proposes to exact for his services. Bateson, who first applied Mendel’s principles to animals, wrote five years before the Mendelian Renaissance in terms which may still be commended to the thoughtful examination of every student of the evolutionary problems:

“Whereas the only possible test of the utility of a structure is
a quantitative one, such a quantitative method of assessment is
entirely beyond our powers. To know that the presence of a certain
organ may lead to the preservation of the race is useless, if we
cannot tell how much preservation it can effect... unless we know
also the degree to which its presence is harmful, unless, in fact,
we know how its presence affects the profit and loss account of the
organism.” (_Materials for the Study of Variation_).

That animals do in fact display many structural characteristics which are in no sense useful to them is generally admitted to-day. It thus becomes as much the function of any theory of the evolutionary process to explain the origin of useless as to explain the origin of useful devices. There is a practical limit to the use of the concept of adaptation in morphology. There is a no less obvious limit to the use of the concept of adaptation in physiology. An animal is a self-regulating system up to a point; but it cannot in every contingency take arms against a sea of troubles and by opposing end them. If we could define in some general terms where this limit lies, we should be justified in speaking of a principle of adaptation in the sense that we speak of a principle of conservation of matter. The ideally self-regulating unit of living matter endowed with the secret of perpetual youth is as imaginary as the Economic Man. At present the fact that organisms cease to regulate themselves and die is as fundamental a problem of biology as the converse fact that they regulate themselves and thereby continue to live. The fact that the organism has a good deal of useless anatomical equipment seems to be as true as the fact that on the whole its anatomy is suited to the requirements of its surroundings. In whichever way we employ the term adaptation we are forced to the conclusion that it is only legitimate to speak of a principle of adaptation in the sense in which we speak of the active principle of the thyroid gland. Adaptation defines a field of problems which await solution. In that sense the concept of adaptation is as fundamental to mechanistic as to any other theories of the organism.

§3

This is not what is generally meant when it is said that adaptation is a fundamental principle of biological enquiry. I believe that it is the only legitimate sense in which it can be said that there is a biological principle of adaptation. It seems to me that, when we go further and put more than this into our concept of adaptation, we are driven to formulating the problems of biology in a wrong way. By inventing hypotheses to explain facts which do not exist, we then proceed to give false interpretations of the significance of facts that do exist.

When the principle of adaptation is treated as a principle which enables us to predict conclusions, it constantly leads us to fantastic distortions of what really happens. If I wished to illustrate this in connexion with the self-regulating aspect of the concept of adaptation, I could not do better than refer to current speculations about the rôle of the ductless glands in the economy of the organism. The physiologist who interprets his field of observation in a manner analogous to that of the physicist and chemist realizes that we have no reason to believe that every chemical entity found in the animal body is necessary or even useful to its owner. He will not therefore draw any conclusions of a far-reaching nature from the discovery that a certain tissue extract has highly specific physiological properties, unless he can show that the removal of the tissue itself produces effects of an opposite nature to those which ensue on injecting its active constituent. The student of ductless glands who regards adaptation as a principle to be applied rather than as field to be explored will not be held back by such restraint. We must thank the “principle” of adaptation in endocrinology for the romantic guess-work of that school which undertakes to interpret the whole of human history in terms of a glandular explanation of temperament. Most speculations on which the glandular theory of temperament are based have their only experimental basis in the presence of supposedly specific active substances in one or other tissue extract. A “principle of adaptation” does not assist us to understand why the pituitary gland of a fish should contain one specific constituent which produces expansion of the black pigment cells in the skin of a frog, another specific constituent which causes the uterus of the mammal to contract, and yet a third which produces a specific fall of blood pressure in the bird and a specific rise of blood pressure in the mammal.

It is especially in the field of evolutionary biology that we must look for most guidance, because the concept of adaptation has occupied such a prominent part in the evolutionary controversy. As an example of how “the principle of adaptation” leads to incorrect conclusions I need cite only one example from an exceedingly able and provocative address of Professor D. M. S. Watson.

“It is not unusual for a student of fossils to discuss the habits
of an extinct animal on the basis of a structural resemblance of
its ‘adaptive features’ with those of a living animal and then to
pass on to make use of his conclusions as if they were facts in
the discussion of an evolutionary history or of the mode of origin
of a series of sediments. In extreme cases such evidence may be
absolutely reliable: no man faced with an ichthyosaur so perfectly
preserved that the outlines of its fins are visible can possibly
doubt that it is an aquatic animal, and such a conclusion based on
structure is supported by the entire absence of ichthyosaurs in
continental deposits of appropriate ages and their abundance in
marine beds. But if extremes give good evidence, ordinary cases are
always disputable. For example, there is, so far as I know, not the
least evidence in the post-cranial skeleton that the hippopotamus
is aquatic; its limbs show no swimming modification whatsoever, and
the dorsal position of the eyes would be a small point on which to
base assumptions. Most palæontologists believe that the dentition
of a mammal, and by inference also that of a reptile or fish, is
highly adaptive, that its character will be closely correlated with
the animal’s food, and that from it the habits of an extinct animal
can be inferred with safety. Here again the extreme cases are
justified, the flesh-eating teeth of a cat and the grinding battery
of the horse are clearly related to diet. Crushing dentitions, with
the modification of skull and jaw shape and of musculature which
go with them, seem equally characteristic. I had always believed
that the horny plates and the jaws of Platypus were adapted to
hard food, and that that animal possessed them, whilst the closely
allied Echidna was toothless, because it was aquatic and lived in
rivers which might be expected to have a rich molluscan fauna which
could serve as food. But the half-dozen specimens whose stomachs I
have opened contained no molluscs whatsoever, and seem to have fed
on insect larvæ, the ordinary soft bottom fauna of a stream.” (_Op.
cit._)

We are now beginning to see that the evolutionists of the nineteenth century focused their attention far too exclusively on adaptation. In other words, they regarded adaptation as a principle like the principle of conservation of matter, one of universal validity within the field of biology. Any theory of evolution has to explain why non-adaptive, as well as adaptive, features arise. In that sense the fundamental problem of evolution is not the origin of adaptation but the origin of species. Both the theories of Lamarck and Darwin implicitly assumed that the differences between species, in the traditional, i.e. Linnæan sense, are mainly utilitarian. Having started with an incorrect apprehension of the facts they proceeded to elaborate hypotheses to account for them. Thence inevitably they drew from these hypotheses an unsatisfactory account of the way in which new species do arise. From the modern standpoint analysis of the species problem does not demand a recognition that species differences are even in the main utilitarian, though such a statement would probably be true of differences between larger units such as genera. Nor from the modern standpoint do the hypotheses of either Lamarck or Darwin give us any clue to the way in which the species barrier, i.e. inability to breed with other species successfully, can have arisen. Anything which remains of the Lamarckian principle in the light of modern research has no special relevance to the origin of adaptations. Whatever remains of the theory of natural selection has been completely divested of the implication that non-adaptive characters were necessarily adaptive at their inception.

A discussion of the fate of the Lamarckian and Darwinian theories must be undertaken elsewhere. Here it is sufficient to point out that both, more particularly the latter, had a peculiarly sterilizing influence on the growth of experimental biology. Obsessed with the principle of universal adaptation which Natural Selection had secularized, zoology, from the publication of the _Origin of Species_ to the rediscovery of Mendel’s Laws, wandered for forty years in a wilderness of phylogenetic speculation. Biological research in the words of Professor Punnett became

“devoted to the construction of hypothetical pedigrees suggesting
the various tracks of evolution.... The result of such work may be
said to have shown that the diverse forms under which living things
exist to-day, and have existed in the past, so far as palæontology
can tell us, are consistent with the view that they are all
related by the community of descent.... It is obvious that all this
work has little or nothing to do with the manner in which species
are formed.”

According to the Selectionist doctrine in its original form, characters originated and persisted in virtue of their utility and what Darwin somewhat vaguely called “the strong principle of inheritance.” To explain any peculiarity of structure or habit, it became necessary only to show one of two things, either it was useful to its owner or was once useful to an ancestor of its owner. Everything was or had been an adaptation. This resulted in a complete divorce of comparative anatomy from comparative physiology. The morphologist and systematic zoologist regarded it as an impertinence of the physiologist to seek for experimental evidence, where a perfectly good case of adaptation was evident to anyone who would accept their premisses.

I will illustrate this from a field in which I have myself carried out experimental investigations for twelve years. Writing of colour change in frogs Dr. Hans Gadow makes the following remarks in the _Cambridge Natural History_ (_Amphibia and Reptiles_, p. 36):

“Biedermann concludes that the chromatic function of frogs in
general depends chiefly upon the sensory impressions received by
the skin, while that of fishes depends upon the eye. All this
sounds very well, but the observations and experiments are such
as are usual in physiological laboratories, and the frogs, when
absorbed in their native haunts, or even when kept under proper
conditions, do not always behave as the physiologist thinks they
should. There is no doubt that in many cases the changes of colour
are not voluntary but reflex actions. It is quite conceivable that
the sensation of sitting on a rough surface starts a whole train of
processes: roughness means bark, bark is brown, change into brown;
but one and the same tree frog does not always assume the colour of
the bark, when it rests or when it sleeps upon such a piece. He
will if it suits him remain grass green on a yellow stone or on a
white window frame.... The sensory impression received through the
skin of the belly is the same, no matter if the board be painted
white, black or green, and how does it then come to pass that the
frog adjusts its colour to a nicety to the general hue or tone of
its surroundings.”

It is safe to say that no one, unless at the outset prejudiced by the principle of adaptation, could be led to entertain the view that frogs as a rule are able to adjust themselves “to a nicety” to the general hue and tone of their surroundings. The state of the pigment cells in the skin is influenced independently by a number of diverse factors, including moisture, temperature, diffuse light acting on the skin and reflected light acting on the retina of the eye in the opposite sense. Individual frogs differ in basic pattern, but the range of hue between the dark and pale condition for any frog is fixed, as is also true of the proverbial chameleon. When the conditions affecting colour change in a frog are defined, it is possible to predict the pigmentary response of a frog and its time relations with as much confidence as any other physical event in nature. It is, on the other hand, quite impossible to draw any far-reaching conclusions about colour change from uncontrolled observation of the frog in its native haunts, because the number of significant variables is far too numerous to handle in this way. I have quoted this passage to show the attitude which zoologists under the influence of the post-Darwinian tradition adopted towards experimental enquiry of any description. Dr. Gadow applies the “principle of adaptation,” as it was then used in morphology, to the self-regulating aspect of the organism with results which show what might well happen to physiology if the physiologist employed the principle of adaptation as the chemist employs the principle of conservation of matter.

Ecology, or the study of the relation of species to particular types of environment, provides a clear illustration of the progress that has been achieved by detailed study of physiological mechanisms in place of the speculative application of the principle of “adaptation.” Krogh and his pupils have made a special study of the physico-chemical properties of the blood pigments of the lower organisms, and have thereby thrown a good deal of light on the conditions which determine their ecological distribution. Let us take the case of two common bony fishes, the carp and the trout. It is a matter of common experience that in nature the trout will only live in running streams. It can be kept with great difficulty in aquaria, if special precautions for aerating the water are taken. The carp will live in still water, where the oxygen content is low, and like its ally the goldfish accommodates itself to the aquarium with great ease. The difference between the two types is at once understood, when we know that the hæmoglobin of the carp has a much higher affinity for oxygen than the hæmoglobin of the trout. In consequence the blood of the carp is completely saturated with oxygen when the oxygen content of the water in which it swims is far below that which is in equilibrium with the oxygen pressure of the atmosphere. The blood of the trout on the other hand is only fully saturated with oxygen when the water is itself nearly saturated.

The concentration of salts in the blood of fishes like the trout and carp is kept constant at a level below that of sea water. The concentration of dissolved substances in the blood of sharks and dogfishes which are all marine is in equilibrium with the osmotic pressure of the sea. The respiratory centre of the wrasse is paralysed at 60° C. {sic}, while the heart of the English dogfish shows irreversible changes above 18° C. Taking these facts together we can deduce a good deal about the viability of a species in a given locality. A fish like the skate placed near the estuary of a large river is forced to remain where the salt concentration is above a certain level. A salmon is not subject to this restraint. Assuming that the fish can pass the estuarine boundary and proceed upstream, two alternatives present themselves. He can remain in the swiftly moving main stream or take to backwaters and stagnant lakes connected with it. If he has the hæmoglobin of a trout, he is committed irretrievably to the former alternative. Being compelled to remain in the swiftly running part of the river bed, he might stay in the lowlands or make for the source, which in general will be much colder. In the case of a fish like the wrasse, whose respiratory centre is paralysed at a temperature of 6° C., the latter course is impossible, if the river rises in a high range. Thus in place of vaguely speculating about how an organism is specially “adapted” to live in some particular place, experimental biology is gathering clearly defined ideas about why an organism cannot live in any place other than that in which it does live.

The idea that a problem can be solved by invoking the principle of adaptation assumes its most grotesque form in Haeckel’s discussion of Recapitulation. The classical example of what is called recapitulation is provided by the gill clefts of vertebrates. All vertebrate embryos have pits or clefts at the sides of the throat, supplied by a characteristic arrangement of blood-vessels. In fishes the clefts acquire filaments richly supplied with blood-vessels, and act as gills. Both the gill clefts and the characteristic arrangement of blood-vessels associated with them persist throughout life. In frogs and salamanders gill filaments are developed in the tadpole stage, but the clefts disappear in adult life and the characteristic arrangement of their blood supply becomes profoundly changed. In Man and most land vertebrates the gill clefts are never used as respiratory organs, and with their blood-vessels disappear at an early stage in development. During the first half of the last century Van Baer, the pioneer embryologist, propounded a generalization which may be stated thus: embryos of different species of animals of the same group are more alike than the adults, and the younger the embryo the greater are the resemblances. This generalization, well illustrated by the gill clefts, was later extended by Haeckel with the sonorous title “Biogenetische Grundgesetz.” It is thus defined by its author: “The history of the fœtus is a recapitulation of the history of the race, or in other words, ontogeny is a recapitulation of phylogeny.”

The way in which the modern geneticist handles the problem of development offers a striking contrast to the attitude of Haeckel and a generation of zoologists unduly preoccupied with the concept of adaptation. A recent investigation from the laboratory of Professor Julian Huxley will illustrate the difference. In the little crustacean _Gammarus_ there are a number of varieties distinguished by the colour of their eyes. All coloured eyes are at an early stage of development colourless. They then become scarlet owing to the formation of a red pigment. They may subsequently darken owing to the deposition of the black substance known as melanin. Varieties with eye colour from a dark red through various grades of chocolate to dark brown and black are distinguished by the time at which the deposition of melanin begins and the rate at which it occurs. Here there is no difficulty in seeing what conditions must be fulfilled in order that a new variety should or should not recapitulate the characteristic of the ancestral stock from which it arises. If a red-eyed variety of Gammarus arose from a white-eyed stock, it would necessarily exhibit the ancestral condition at the beginning of development, because all eyes are at first colourless. If a black-eyed form arose as a sport from a red-eyed stock, it would also recapitulate the ancestral characteristic, because all black eyes are at first red. If a white-eyed form arose as a sport in a red-eyed stock, or a red-eyed form emerged from a black-eyed stock, in neither case would the ancestral condition be manifest at any stage of development. There is no question of the intrinsic usefulness of a new character involved in this. Whether recapitulation does or does not occur here depends upon whether the Mendelian factor which distinguishes a new variety hastens or retards some feature of the developmental process.

Now Haeckel’s “Grundgesetz” implies an additional statement to that contained in Van Baer’s Law. It signifies that the embryonic stages of one form are to be compared with adult rather than embryonic stages of another. This in fact is not correct, as the classical cases of recapitulatory phenomena demonstrate most clearly. The mammalian embryo never possesses true gills. It goes through a stage at which it has the characteristic clefts and arterial arches which in the _fish embryo_ precede the development of functional gills. This is also true of crustacean larvæ. _Sacculina_, the crab gall, passes through the two characteristic larval forms of the true _barnacles_. It has no resemblance to an adult barnacle in any stage. A more serious objection to Haeckel’s way of stating the idea of recapitulation in development is the vagueness it assumes when brought face to face with the exceptions that are as numerous as the applications of the rule. An illustration of the exceptions is provided by eye colour in the human species. It is fairly certain that the blue-eyed condition has arisen as a mutant in a brown-eyed stock; yet the eyes of brown-eyed adults are often blue in the newly born.

It is not difficult to discover in Haeckel’s own writings the train of reasoning which led him to distort the facts of development in stating the law which is often associated with his name.

“The evolution of the fœtus (or ontogenesis),” states Haeckel, “is
a condensed and abbreviated recapitulation of the evolution of the
stem (or phylogenesis); is preserved by a constant heredity; on the
other hand, it becomes less complete in proportion as a varying
adaptation to new conditions increases the disturbing factors in
the development (or cenogenesis). The cenogenetic alterations or
distortions of the original paligenetic course of development take
the form, as a rule, of a gradual displacement of the phenomena,
which is slowly effected by adaptation to the changed conditions
of embryonic existence during the course of thousands of years.
This displacement may take place as regards either the locality or
the time of the phenomenon. The first is called heterotopism, the
second heterochronism.”

So naïve a combination of garrulous teleology and self-contradiction is characteristic of the hopeless confusion of thought which existed in evolutionary biology, while it remained dominated by the principle of adaptation. The larval “adaptations” should on the face of it recapitulate their ancestral story--and so on in endless regression. There is no intelligible meaning in Haeckel’s explanation of the admittedly ubiquitous exceptions to his rule.

Haeckel’s so-called Biogenetische Grundgesetz exerted a profound influence on biology during the second half of the nineteenth century, and perhaps did more than anything else to divert zoologists from the study of activity to the pursuit of insignificant details of no conceivable physiological interest. Instead of furthering the development of zoology as an exact science, it substituted the construction of architectural mnemonics for the search after quantitative laws. With Haeckel’s law is associated an interesting logical fallacy in the development of the argument for evolution. Huxley made a good debating point when he disclosed the embarrassing information that a bishop at one stage of the episcopal life cycle has gill structures like those of a fish. From the standpoint of formal logic the point is worthless. Only the atmosphere of religious propaganda which surrounds the birth of the evolutionary doctrine can explain the perennial reappearance of the contention that recapitulation constitutes an argument _sui generis_ in favour of the doctrine of descent. If experimental breeding taught us that mutant forms recapitulate the characteristics of the stock from which they originate, the resemblance of developmental stages of present-day forms to adult organisms which existed in the geological past would constitute a special consideration in favour of regarding fossil remains as ancestral to contemporary animals. As yet experimental breeding teaches us no such thing. We do not find that a white-eyed fly originating as a sport in a red-eyed stock invariably has red eyes at any prior stage of development. Recapitulatory phenomena are difficult to explain on a theological basis, but they do not constitute a special argument in favour of the evolutionary alternative. To-day biologists are beginning to realize that evolution must furnish an explanation of specific differences which are not adaptive as much as specific differences which are adaptive. With this change of outlook it is becoming possible to discuss the logical status of the evolutionary hypothesis without recourse to arguments which belong more properly to propaganda than to science.