Evolution by "Use"

Jean Baptiste Pierre Antoine de Monet, Chevalier de Lamarck

There are reasons why Lamarck’s system should be of special interest to the student of biology. For it contains the first theory of adaptation through the transformation of species, which is rounded upon bare hypothesis, and it may in this respect be regarded as the pattern for all modern biology. It also gives its name to that school which somewhat vaguely opposes itself to the explanation of everything organic as the product of natural selection and fortuitous variation. And thirdly, the hypothetical processes and substances of this system have now become, in the ordinary course of research, obvious fiction; so that the doctrine reveals at once its true relation to observation, even without the demonstration of the impossibility and self-contradiction of its typical hypotheses. For Lamarck continually boasts of the sure method of observation, and fills his pages with innumerable references to organic phenomena; but the advance of research has shown that he, like the other biologists of hypotheses, was deceiving himself on this score. For, whatever had been the actual qualities of organisms, they would have supported his theory equally well, so long as they were qualities of organisms.

But even apart from the light which the study of Lamarck throws upon biological problems and methods in general, the system itself is of great interest. It is certain that this biologist has been, on the whole, misinterpreted, but, on the other hand, it is not easy to be sure that one understands him. And the confusion has taken place chiefly over that key-word of his system, besoin, or need. This word has frequently been rendered "desire," and Lamarck has often more than a trace of this meaning in his use of it. But, on reading the whole development of his argument, one immediately finds that neither interpretation may be used exclusively, and that, in fact, besoin is a conception which, for the purposes of the theory, must remain undeveloped and undefined. Use the conception of need alone, and the theory is inadequate; restrict yourself to the conception of desire, and the whole theory becomes ridiculous, as flippant controversialists have not been slow to find. It is certainly more than need, and as certainly, it is less than desire. It probably appeared to Lamarck to have quite a definite meaning, requiring no further analysis. One can only suppose that he was unconscious of his easy bridge from the ideal relation of necessity to the psychological fact of desire—from the logical form to the phenomenal process.

In the need, or besoin, we have not, of course, to do with a mere negation. It is not a mere being without or not having. The organism has some kind of reference to the thing which is needed. And since every part of an organism is needed by the rest and by circumstances, it is not difficult to find, in this need, a general principle for the origin of all organic characteristics. All characteristics are alike in this point, though in no other; for simply as parts or organisms, they have relations of [p.414] necessity with one another. But a mechanism, by which this form of necessity may create the particulars, is wanting to observation. Yet such a mechanism becomes desirable, in order that the emptiness of the theory may be, if only apparently, filled up. The logical distinction must therefore, as we are well accustomed to find, become a quasi-phenomenal difference; and thus there arises the Lamarckian Desire, which is more like Hartmann’s Unconscious than it is like anything else, being quite as metaphysical in its origin as is the latter. I shall not attempt the difficult historical question as to what Lamarck supposed his conception of need to include. For our present purpose I merely take his work as it stands, and study it in relation to the problem of adaptation, and watch its development of the old quasi-psychical principle. And I here set down certain important passages from the "Philosophic Zoologique," chapter vii.

"It is evident that the observed form of animals is the product, on the one hand, of the ever-increasing complexity of organization, which tends to form a regular gradation; and on the other hand, of the influences of a multitude of very various circumstances, which tend continually to destroy the regularity of that gradation of the increasing complexity of organization. But I must explain my meaning in these expressions. ’Circumstances affect the form and organization of animals’ means that the former, in becoming very different, change, in course of time, even the form and organization by proportionate modifications. Certainly it would be a mistake to use these words literally, for, whatever be the circumstances, they have no directly modifying effect whatever on form and organization. But great changes in circumstances give rise to great changes in the needs of animals, and such changes in their needs necessarily give rise to changes in their actions. And if the new needs become constant or very lasting, the animals take on new habits which are as lasting as the needs which gave rise to them. It is easy to demonstrate this; indeed, it is obvious without explanation. So that it is evident that a great change in circumstances, when it has become constant for a race of animals, leads those animals into new habits. And, if the new circumstances which have become permanent for a race of animals have given rise to new habits in them (that is, have impelled them to new actions which have become habitual), the result will be the use of such a part in preference to that of such another, and in certain cases the total disuse of such a part as has become useless. Now, none of this is hypothesis or my own opinion; it is, on the contrary, truth which only needs attention and observation of facts to become evident." (P. 222.) [p.415]

Such, then, is the process of adaptation, to some extent in the individual, and altogether in the race. And the process is the same in each case. Moreover, the same process might be thought to underlie the adaptation of part to part within the development of the individual. A race of animals comes into certain circumstances, or is in them (for the change is not essential to the argument), and suffers no direct change from these circumstances. The latter, however, affect the needs, and the needs condition the actions, which, as habits, affect the form and organization. Just so in the theory of natural selection, the circumstances do not directly affect the race, but all adaptation is referred to the indirect affection of form by the environment. This indirectness of the relation of the individual to circumstance is the form which is first attained by all theories of adaptation, and the special manner of it is a secondary point.

The meaning of this indirectness is that no particular of the organism is changed, except through the unity of the organism, and that changes in organisms have the appearance of being purposeful responses to, rather than mere results of, the changes in the circumstances. And the theories which we are studying have no other object than to derive the present purposeful reaction from a series of direct causes which operated long ago. But it must be noticed that this element of theory, which is as strongly held by Weismann as by Lamarck, completely does away with all those analogies for organic adaptation which are drawn from inorganic things. You may see the coat of rust round a ball of iron, or the shore round a bay, given as parallels to the adaptation of one part of the organism to another or of the whole to its environment. In such cases the relation is perfectly direct, and the change in one element involves a calculable complementary change in the other. But it would appear as though such a direct action of circumstances on organic form takes place, if at all, only within the narrowest limits, either in the individual or in the race. We have seen that the nutritive conditions of form are not answered in the individual by results such as one would expect from the conditions, or such as one could give in parallel degrees with the conditions. The determination of sex, for instance, is hardly the direct result of food supply, in the same sense as the shape of the bay is the direct result of the shape of its shore; and the difference does not seem to be merely that of the extent of our knowledge. Let a race of birds take to the water, and, provided that such changes do in truth occur, its toes become webbed and it secretes oil for its feathers. But these changes are hardly the direct result of cold and wet. In the great majority of cases, one can see the advantage of a structure, and when its advantage is not evident, it is looked for as probably discoverable. But either one cannot speak of an immediate cause at all, or one cannot relate that cause to the advantage. This is notably the case in the study of ontogeny. The events which produce muscle have apparently nothing to do with contraction; bone is not, apparently, produced by stress, nor, so far as one can see, does nerve arise in the individual by feeling. Still this may be only apparently so. Of course embryonic parts have functions, and it is probable that these are not incomparable to their adult functions. But, in fact, we are accustomed to consider rather the end than the cause of the organic part; and when we attempt to find the end as cause, it is plain that the end must operate indirectly, for there are other immediate causes which can be found by research. Hence there arises the necessity of making adaptation indirect, and Lamarck, as we have seen, is plain on this point. What qualities the organism has, it has because it needs them and because they are purposive; for the form is not immediately referable to the circumstances in which it finds itself. That is the beginning and end of the theory, and the rest is only the very vague and hesitating attempt to show how the need can bring about the new structure. That this is Lamarck’s central thought appears from his summary of the theory, which includes his two well known laws. He says: "In order to see the true order of things one must recognize:—

"(1) That every change which is at all considerable and continuously maintained in the circumstances of each race of animals, affects in it a real change in their needs.

"(2) That every change in the needs of animals necessitates other actions on their part for the satisfaction of the new needs, and in consequence, other habits.

"(3) That since every new need requires new actions to satisfy it, it demands of the animal which experiences it either the more frequent use of such a part as was formerly less used, so that it becomes considerably developed and enlarged; or the use of new parts which insensibly arise in the organism from the needs, by the efforts of its inner feeling, as I shall presently show from known facts. And so, to arrive at the true cause of so many different forms and so many various habits as are given in the animal world, one must recognize that the infinitely diversified but slowly changing circumstances in which the animals of each race have successively been placed, have brought about in each race new needs, and consequently changes in their habits. As soon as one has recognized this incontestable truth, it will be easy to perceive how the new needs can have been satisfied and the new habits taken on, if one attends to these two laws of nature, which have always been corroborated by observation.

"FIRST LAW.—In every animal which has not passed the limits of its development, the more frequent and sustained use of any organ gradually strengthens that organ, develops it, increases its size, and gives it a strength proportional to the use in question; while the constant disuse of such an organ insensibly weakens and deteriorates it, progressively diminishes its faculties, and finally results in its disappearance.

"SECOND LAW.—All that nature has caused to be acquired by or lost to individuals through the influence of the circumstances to which their race has long been exposed—and therefore through the predominant use of an organ, or through the constant disuse of a part—she preserves, by reproduction, for the new individuals which come from them, provided that the acquired changes are common to the two sexes, or to those which have produced the new individuals." (Vol. i., p. 234.)

So far, except for the allusion to the "sentiment interieur," the conception of need is simply that of necessity, and we have no psychological hypothesis. But the principle later develops into desire in such instances as the following:—

"The bird, which is attracted into the water by need, in order that it may find the food by which it lives, spreads out its toes when it would strike the water and move over the surface. The skin which unites the base of the toes gains the habit of stretching, because of this ceaselessly repeated spreading of the toes. Thus, in course of time, the wide membranes which unite the toes of ducks and geese are found as we see them. The same efforts to swim have spread out even the membranes between the toes of frogs, turtles, otters, and beavers. The bird, on the other hand, which is accustomed by its manner of life to sit upon trees, and which comes of individuals which had all contracted this habit, has toes which are necessarily longer than, and differently formed from those of the aquatic animals above mentioned. Its nails have become lengthened in course of time; they are sharpened and bent into hooks in order to dutch the branches upon which the animal so often rests. Even so one feels that the bird of the shore which does not care to swim and which nevertheless needs to approach the edge of the water to find its prey, is continually in danger of sinking into the mud. That bird, therefore, trying to avoid plunging its body into the water, makes every effort to stretch and lengthen its feet. The result is that the long continued habit of stretching and lengthening its feet which is contracted by that bird and by all of its race, raises the individuals of the race, as it were, upon stilts, inasmuch as they gradually gain long and naked feet.

Should an animal make repeated efforts to lengthen its tongue, in order to satisfy its needs, the tongue will acquire considerable length; should it need to seize anything with that organ, the latter will divide and become forked. Needs, always caused by circumstances, and the consequent sustained efforts to satisfy them, can do more than to modify organs, for they can even displace those organs when some of the needs make this necessary." (Vol. i., p. 248.)