The late Sir Charles Lyell mentions in his Antiquity of Man how Dr. Sumner, the late Archbishop of Canterbury, brought out in strong relief fifty years ago, in his Records of Creation, one essential character separating man from the brute. As the same argument is still being “brought out,” and is, on the face of it, exceedingly plausible, and as the answer to it has to do with the brain, it cannot be passed over. Dr. Sumner said: “It has been sometimes alleged, and may be founded on fact, that there is less difference between the highest brute animal and the lowest savage than between the savage and the most improved man. But, in order to warrant the pretended analogy, it ought to be also true that this lowest savage is no more capable of improvement than the chimpanzee or orang-outang.” This objection is met by some such consideration as the following:—When you examine the enormous difference in the formation of the skull in man and ape (look, for instance, at plate xvii., vol. ii. of Haeckel’s Evolution of Man), and when you remember that this sets hard at an early date, you surely have a good reason for limited improvability. Further, the brain of even the lowest savage represents a development of some half a million years above the ape along the line of intelligence. How, then, can we dream of making this up in one or a few generations by artificial training of the ape? Lastly, we have the enormous leverage of language, the inherited wealth of thousands of speaking generations, and an incalculable aid to thought. How much is the intelligence of the Microcephalæ, the clucking “small heads” lately on show at the Hippodrome, capable of rapid improvement? Our experiments do not show that the ape is not improvable, but only that we cannot, in a single generation, lift it over a gulf representing 500,000 years of human development. How can we expect it?
The Blood.—In the last few years an astonishing confirmation of our relationship to the anthropoid ape has been discovered. We are blood relations. Elie Metchnikoff, Professor at the Pasteur Institute, shows this clearly in his book, The Nature of Man.[34] Until quite recently it was not known how to distinguish human blood from that of other mammals. A method giving conclusive results has now been discovered, and is used in forensic medicine. The same method has been employed in comparing the blood of man and the anthropoid apes, resulting in the discovery[35] that, in their case, there is practically no blood difference whatever!
THE REVELATIONS OF EMBRYOLOGY.
The opponents of Evolution used to appeal to the special features of human embryology, which were supposed to distinguish man from all the other mammals; but in 1890 Emil Selenka proved that the same features are found in anthropoid apes, especially in the orang, while the lower apes are without them.
“When Huxley wrote, the embryological history of anthropoid apes was practically unknown. Darwin, Vogt, and Haeckel, in their attempts to support the theory of the animal origin of man, had not sufficient knowledge of the embryology of monkeys. It is only recently that important work on this subject has been published.... The placenta often gives information of great importance in the classification of mammals. It is sufficient to glance at the zonary placenta of dogs and seals to be convinced of the relationship of these two species which at first sight seem so different. Now, the placentas of all the anthropoid apes examined up to the present are of the same discoid type as that of man. The arrangement of the umbilical cord of man, which was formerly considered as quite peculiar to him, is found in anthropoid apes, as has been established by Deniker and Selenka. It is striking that the anthropoids resemble man rather than the lower monkeys in the relation of the fœtus to the fœtal membranes. With regard to the embryos themselves, the similarity between those of monkeys and man is very great.... The youngest stages of human development that have been obtained can hardly be distinguished from those of the lower monkeys either in position or shape. More advanced stages exhibit greater differentiation, and the later embryos of man resemble those of anthropoids much more closely than those of the lower monkeys. The resemblance between the nearly mature fœtus of anthropoids and human embryos of about the sixth month is evident enough.”[36]
We are thus bound, in all honesty, to own up to our ape-like progenitors. But this is only a small portion of the wonderful tale told by Embryology. “Man is developed from an ovule about 125th of an inch in diameter, which differs in no respect from the ovules of other animals,”[37] and, marvellous to relate, from that stage upwards the embryo is one continuous epitome of the history of man’s evolution from lower forms of life.[38] Up to a certain point the germs, not only of all mammals, but of all vertebrate animals, fishes, reptiles, and birds, are scarcely distinguishable. A sceptic may convince himself by studying the plates given in Haeckel’s The Evolution of Man, and especially plates ix. to xiv., where the embryos of various animals are compared. At the more advanced stage, where the embryo has already passed the reptilian form, we find that for a considerable time the line of development remains the same as that of other mammalia. The resemblance, for example, after the first four weeks’ growth, between the embryo of a man and that of a dog is such that it is scarcely possible to distinguish the one from the other. Even at the age of eight weeks the embryo man is an animal with a tail, hardly to be distinguished from an embryo puppy.[39] After this period the embryo emerges from the general mammalian type into the special order of primates to which man belongs. Thus does the growth of the egg from which man springs compress into a few weeks the results of millions of years, and set before us the history of his development from fish-like and reptilian forms (which, as we have seen, p. 211, Mr. Gladstone deemed so contemptible and “fallen from greatness”), and of his more immediate descent from a hairy, tailed quadruped, the extinct common ancestor of man and monkey. As evolution proceeds the embryo rises up to man, and the differences specialising the human infant at its birth, such as the largeness and more complex convolutions of the brain, become more and more accentuated as its growth proceeds.
Regarding the question of “gaps,” we have to bear in mind that it is part of the evolutionary theory that the active processes of evolution have very largely ceased, that existing forms are but a surviving remnant with enormous gaps, and that the survivors are so fitted at present to their surroundings that evolutionary forces are causative of equilibrium rather than change. We have already seen, too, that in the struggle for existence it is among the closely-allied species that the contest is more strenuous, and that the weakest, or least fitted to survive, has to go to the wall—to be wiped out. Thus it is that there is a tendency for species to become extinct, and for the gaps to be widened. The extraordinary thing is not that we have so little direct evidence of descent, but that we have so much. That there are not more links missing is due principally to the discovery of fossil remains. When an animal dies, the probabilities are, of course, enormously against geological preservation of its bones, yet the gaps are continually being filled up by geological finds, and, though the remaining gaps may be great, they are not unaccountable.
I must now pass on to the remaining set of proofs of our origin.
THE TALE TOLD BY THE USELESS RUDIMENTARY ORGANS.
Perhaps nothing furnishes a more conclusive proof of our animal origin than the study of rudimentary structures—muscles, sense-organs, hair, bones, reproductive organs, etc. There are some which are “either absolutely useless, such as the mammæ of the male quadrupeds or the incisor teeth of ruminants which never cut through the gums; or they are of such slight service to their present possessors that we cannot suppose that they were developed under the conditions which now exist.”[40] Of useless rudimentary organs, or parts of organs, there are not less than one hundred and seven in man.[41] To this category belong the coccyx—the vestige of a tail—the muscles of the ear, the vermiform appendage, etc.