As we shall see, von Baer adopted in later years the same attitude to Darwinism as he did to the evolution theories in vogue in his youth.
Although in the twenty or thirty years before the publication of the Origin of Species (1859) no evolution theory of any importance was published, and although the great majority of biologists believed in the constancy of species, there were not wanting some who, like von Baer, had an open mind on the subject, or even believed in the occurrence of evolutionary processes of small scope. Isidore Geoffroy St Hilaire, the son of the great Etienne Geoffroy St Hilaire, seems to have held that species might be formed from varieties. The law which L. Agassiz thought he could establish,[349] of the parallelism between palæontological succession, systematic rank, and embryological development, tended to help the progress of evolutionary ideas. J. V.. Carus, who afterwards became a supporter of Darwin, seems already, in 1853, to have inferred from Agassiz's law the probability of evolution.[350]
But no evolution theory was taken very seriously before 1859, when the Origin of Species was published.
Like Lamarck, Charles Darwin was, neither by inclination nor by training, a morphologist. In his youth he was a collector, a sportsman and a field geologist. His voyage round the world on the Beagle aroused in him keen interest in the problem of species—their variety, their variation according to place and time, their adaptedness to environment. The conviction gradually took possession of his mind that the puzzling facts of geographical range and geological succession which he observed wherever he went were explicable only on the hypothesis that species change. He was not satisfied with the theories of evolution that had been proposed by his grandfather, by Lamarck, and by E. Geoffroy St Hilaire—he did not indeed understand these theories any too well. He resolved to work out the problem in his own way, for his own satisfaction. He tells us all this very clearly in his autobiography. "During the voyage of the Beagle I had been deeply impressed by discovering in the Pampean formation great fossil animals covered with armour like that on the existing armadillos; secondly, by the manner in which closely allied animals replace one another in proceeding southwards over the continent; and thirdly, by the South American character of most of the productions of the Galapagos archipelago, and more especially by the manner in which they differ slightly on each island of the group; some of the islands appearing to be very ancient in a geological sense.
"It was evident that such facts as these, as well as many others, could only be explained on the supposition that species gradually become modified; and the subject haunted me. But it was equally evident that neither the action of the surrounding conditions, nor the will of the organisms (especially in the case of plants) could account for the innumerable cases in which organisms of every kind are beautifully adapted to their habits of life—for instance, a woodpecker or a tree-frog to climb trees, or a seed for dispersal by hooks or plumes. I had always been much struck by such adaptations, and until these could be explained it seemed to me almost useless to endeavour to prove by indirect evidence that species have been modified."[351]
All Darwin's varied subsequent work revolved round these, for him, essential problems—How do species change, and how do they become adapted to their environment? He never ceased to be essentially a field naturalist, and his theory of natural selection would have been an empty and abstract thing if his vast knowledge and understanding of the "web of life" had not given it colour and form. He never lost touch with the living thing in its living, breathing reality—even plants he rightly regarded as active things, full of tricks and contrivances for making their way in the world. No one ever realised more vividly than he the delicacy and complexity of the adaptations to environment which are the necessary condition of success in the struggle for existence. Almost his greatest service to biology was that he made biologists realise as they never did before the vast importance of environment. He took biology into the open air, away from the museum and the dissecting-room.
Naturally this attitude was not without its drawbacks. It led him to take only a lukewarm interest in the problems of morphology. It is true he used the facts of morphology with great effect as powerful arguments for evolution, but it was not from such facts that he deduced his theory to account for evolution. It is questionable indeed whether the theory of natural selection is properly applicable to the problems of form. It was invented to account for the evolution of specific differences and of ecological adaptations; it was not primarily intended as an explanation of the more wonderful and more mysterious facts of the convenance des parties and the interaction of structure and function. Perhaps Darwin did not realise this inner aspect of adaptation quite so vividly as he did the more superficial adaptation of organisms to their environment. It was, perhaps, his lack of morphological training and experience that led him to disregard the problems of form, or at least to realise very insufficiently their difficulty.
It is in any case very significant that only a small part of his Origin of Species is devoted to the discussion of morphological questions—only one chapter out of the fourteen contained in the first edition.
Though the theory of natural selection took little account of the problems of form, Darwin's masterly vindication of the theory of evolution was of immense service to morphology, and Darwin himself was the first to point out what a great light evolution threw upon all morphological problems. In a few pages of the Origin he laid the foundations of evolutionary morphology.
We have here to consider his interpretation of morphological facts and its relation to the current morphology of his time.