Thomas Henry Huxley; A Sketch Of His Life And Work

by Sir P. Chalmers Mitchell

"All that can be ascertained concerning the structure, succession of conditions, actions, and position in space of the earth, is the matter of its natural history. But, as in Biology, there remains the matter of reasoning from these facts to their causes, which is just as much science as the other, and indeed more; and this constitutes geological ætiology.

"Having regard to this general scheme of geological knowledge and thought, it is obvious that geological speculation may be, so to speak, anatomical and developmental speculation, so far as it relates to points of stratigraphical arrangement which are out of reach of direct observation; or, it may be physiological speculation so far as it relates to undetermined problems relative to the activities of the earth; or, it may be distributional speculation, if it deals with modifications of the earth's place in space; or, finally, it will be ætiological speculation if it attempts to deduce the history of the world, as a whole, from the known properties of the matter of the earth, in the conditions in which the earth has been placed."

Huxley then proceeded to shew that uniformitarianism and catastrophism had neglected this last and most important branch of geology, the attempt to trace the interaction of causes which had brought the world into its present condition. He gave a striking display of the wide knowledge of his reading by going back to the foundation of this branch of modern science, and giving a masterly account of the then little-known treatise of Immanuel Kant, who in 1775 had written An Attempt to Account for the Constitutional and Mechanical Origin of the Universe upon Newtonian Principles. Next he declared that evolution embraced all that was sound in both catastrophism and uniformitarianism while rejecting the arbitrary limits and assumptions of both.

Finally he came to the great question to which these observations upon the existing schools of geology had led. The most distinguished physicist of the age, then Sir William Thomson, now Lord Kelvin, and Huxley's immediate successor in the Presidential Chair of the Royal Society, had stated that the English school of geology had assumed an impossible age for the earth. By physical reasonings, Thomson stated that he was able to prove "That the existing state of things on the earth—all geological history showing continuity of life—must be limited within some such period of time as one hundred million years." This pronouncement had been received with acclamation by those who feared the geological and biological sciences, as a sign of internal dissensions within the house of science. Huxley, then, as all through the latter part of his life, at once constituted himself the champion of science, and, taking Thomson's arguments one by one, shewed by a series of masterly deductions from known facts that there was a great deal to be said for the other side, and that physicists were as little certain as geologists could be of the exact duration of time that had elapsed since the dawn of life. His plea for more time since the cooling of the globe than physicists were willing to allow remains one of the classics of geological literature. But he carried the question much farther. The inference which was widely drawn by the enemies of evolution from the arguments of Sir William Thomson was that if geologists had overestimated the age of the cooled earth there was not time for the evolution of animals and plants to have taken place. Huxley pointed out a fact which should be quite obvious, but which even yet is frequently neglected. The evidence for the gradual appearance of life in the past history of the earth depends simply on the fact that the successive forms of life appear in successive strata, and the length of time taken for these changes simply depends upon the length of time which was taken up by the formation of the strata. Our only reason for supposing the evolution of life, made plain by fossil records, to have taken place very slowly is that geologists have stated that the deposition of the strata took place very slowly. Whether these strata were deposited slowly or less slowly, we know that the forms of life changed at the same rate.

"Biology takes her time from geology. The only reason we have for believing in the slow rate of change in living forms is the fact that they persist through a series of deposits which, geology informs us, have taken a long while to make. If the geological clock is wrong, all the naturalist will have to do is to modify his notion of the rapidity of change accordingly; and I venture to point out that, when we are told that the limitation of the period during which living beings have inhabited this planet to one, two, or three hundred million years requires a complete revolution in geological speculation, the onus probandi rests on the maker of the assertion, who brings forward not a shadow of evidence in its support."

Perhaps, although this is now an old controversy, it is worth while to recall that the keenness of Huxley's language was not directed against Sir William Thomson, between whom and Huxley there was no more than the desire to argue out an interesting scientific question upon which their conclusions differed, but between Huxley and those outsiders who were always ready to turn any dubious question in science into an argument discrediting the general conclusions of science.

The last time that Huxley occupied the Presidential Chair of the Geological Society was in 1870, and he occupied his Presidential address by a review of the "old judgments" which he had given in the course of his first address in 1862. The address was entitled "Palæontology and Evolution," and the most important part of it was a complete withdrawal of the fears he had expressed that geology would not supply definite evidence of the transformation of species. Important discoveries had come thick and fast; and, at least in the case of the higher vertebrates, he declared that, however one might "sift and criticise them," they left a clear balance in favour of the doctrine of the evolution of living forms one from another. But, with his usual critical spirit, examining arguments that bore against a conclusion for which he hoped almost more stringently than arguments apparently favourable to what he expected to be true, Huxley made an important distinction, the value of which becomes more and more apparent as time goes on. In the first flush of enthusiasm for Darwinism, zoölogists and palæontologists allowed their zeal to outrun discretion in the formation of family trees. They examined large series of living or extinct creatures, and so soon as they found gradations of structure present, they arranged their specimens in a linear series, from the simplest to the most complex, and declared that the arrangement was a representation of the family tree. The fact that the line of descent apparently could have followed along the direction they suggested they were inclined to take as evidence that it had so followed. Huxley made the most careful distinction between what he called intermediate types and types with a right to be placed in linear order,

Every fossil which takes an intermediate place between forms of life already known may be said, so far as it is intermediate, to be evidence in favour of evolution, inasmuch as it shews a possible road by which evolution may have taken place. But the mere discovery of such a form does not, in itself, prove that evolution took place by and through it, nor does it constitute more than a presumptive evidence in favour of evolution in general. The fact that Anoplotheridæ are intermediate between pigs and ruminants does not tell us whether the ruminants have come from the pigs or the pigs from the ruminants, or both from Anoplotheridæ, or whether pigs, ruminants, and Anoplotheridæ; alike may not have diverged from some common stock.

A familiar instance will make the point at issue plain. Everyone knows that in many respects, in the structure of the skeleton, and the curve of the backbone, and in the development of the brain, the man-like monkeys, the gorilla and its allies, are intermediate between man and the lower monkeys. In the early days of evolution it was assumed frequently that the gorilla, etc., were therefore to be regarded as ancestors of man, and they appear as such in more than one well-known treatise on evolutionary biology. We now know that it is exceedingly probable that the gorilla and its allies, although truly intermediate types, and truly shewing a possible path of evolution from the brute to man, are not the actual ancestors of man, but cousins, descendants like man from some more or less remote common ancestor. And the tendency of recent advances in knowledge is more and more to throw stress on the value of Huxley's distinction, and to minimise confusion between "intermediate" and truly ancestral types.