Lamarck sums up as follows:—"By the four laws which I have just enunciated all the facts of organisation seem to me to be easily explained; the progression in the complexity of organisation of animals, and in their faculties, seems to me easy to conceive; so, too, the means which Nature has employed to diversify animals, and bring them to the state in which we now see them, become easily determinable" (p. 168).
It is never made quite clear, we may note in passing, how far his second and third laws tend to bring about an increase in complexity, in addition to diversifying animals.[343]
"The function creates the organ," this would seem to be the kernel of Lamarck's doctrine. But how does he reconcile this essentially vitalistic conception with his strictly materialistic philosophy?
We have seen that irritability, the sentiment intérieur, and intelligence itself, are the effects of organisation. We are told farther on that both the sentiment and intelligence are caused by nervous fluids. A great part of both the Philosophie zoologique and the introduction to the Animaux sans Vertèbres is given up to the exposition of a materialistic psychology of animals and man, based entirely upon this hypothesis of nervous fluids. Thus habits are due to the fluids hollowing out definite paths for themselves.
The sentiment intérieur acts by directing the movements of the subtle fluids of the body (which are themselves modifications of the nervous fluids) upon the parts where a new organ is needed. But if it is itself only a result of the movement of nervous fluids? Again, how can a need be "felt" by a nervous fluid? This is an entirely psychological notion and cannot be applied to a purely material system. Whence arises the power of the sentiment intérieur to canalise the energies of the organism, so to direct and co-ordinate them that they build up purposive structures, or effect purposive actions (as in all instinctive behaviour)? Either the sentiment intérieur is a psychological faculty, or it is nothing.
There is no doubt that, as expressed by Lamarck, the conception conceals a radical confusion of thought. It is not possible to be a thorough-going materialist, and at the same time to believe that new organs are formed in direct response to needs felt by the organism. Lamarck could never resolve this antinomy, and his speculations were thrown into confusion by it. To this cause is due the frequent obscurity of his writings.
Should we be right in laying stress upon the psychological side of Lamarck's theory, and disregarding the materialistic dress in which, perhaps under the influence of the materialism current in his youth, he clothed his essentially vitalistic thought? Everything goes to prove it—his constant preoccupation with psychological questions, his tacit assimilation of organ-formation to instinctive behaviour, his constant insistence on the importance of besoin and habitude.
Let us not forget the profundity of his main idea, that, exception made for the lower forms, the animal is essentially active, that it always reacts to the external world, is never passively acted upon. Let us not forget that he pointed out the essentially psychological moment implied in all processes of individual adaptation. With keen insight he realised that conscious intelligence counts for little in evolution, and focussed attention upon the unconscious but obscurely psychical processes of instinct and morphogenesis.
Not without reason have the later schools of evolutionary thought, who developed the psychological and vitalistic side of his doctrine, called themselves Neo-Lamarckians.
We shall say then that Lamarck, in spite of his materialism, was the founder of the "psychological" theory of evolution.