Again and again we hear and read, even in scientific circles and journals, that Darwinism breaks down at many points, that it is insufficient, and even that it has quite collapsed. Even the assurances of its most convinced champions are rather forced, and are somewhat suggestive of bills payable in the future.8 But here again it is obvious that we must distinguish clearly between the Theory of Descent and Darwinism. Of the Theory of Descent it is by no means true that it has “broken down.” With a slight exaggeration, but on the whole with justice, Weismann has asserted that the [pg 098] Theory of Descent is to-day a “generally accepted truth.” Even Weismann's most pronounced opponents, such as Eimer, Wolff, Reinke, and others, are at one with him in this, that there has been evolution in some form; that there has been a progressive transformation of species; that there is real (not merely ideal) relationship or affiliation connecting our modern forms of life, up to and including man, with the lower and lowest forms of bygone Æons.

The evidences are the same as those adduced by Darwin and before his time, but they have been multiplied and more sharply defined:—namely, that the forms of life can be arranged in an ascending scale of evolution, both in their morphological and their physiological aspects, both as regards the general type and the differentiation of individual organs and particular characters, bodily and mental. All the rubrics used by Darwin in this connection, from comparative anatomy, from the palÆontological record itself, and so on, have been filled out with ever-increasing detail. PalÆontology, in particular, is continually furnishing new illustrations of descent and new evidence of its probability, more telling perhaps in respect of general features and particular groups than in regard to the historical process in detail. For certain species and genera palÆontology discloses the primitive forms, discovers “synthetic types” which were the starting-point for diverging branches of evolution, bridges over or narrows the yawning gulfs in evolution by the discovery of [pg 099] “intermediate forms”; and, in the case of certain species, furnishes complete genealogical trees. The same holds true of the facts of comparative anatomy, embryology, and so on. In all detailed investigations into an animal type, in the study of the structure, functions, or the instincts of an ant, or of a whale or of a tape-worm, the standpoint of the theory of descent is assumed, and it proves a useful clue for further investigation.

In regard to man—so we are assured—the theory finds confirmation through the discovery of the Neanderthal, Spy, Schipka, La Naulette skulls and bones—the remains of a prehistoric human race, with “pithecoid” (ape-like) characters. And the theory reaches its climax in Dubois' discovery of the remains of “Pithecanthropus,” the upright ape-man, in Java, 1891-92, the long sought-for Missing Link between animals and man;9 and in the still more recent proofs of “affinity of blood” between man and ape, furnished by experiments in transfusion. Friedenthal has revived the older experiments of transfusing the blood of one animal into another, the blood of an animal of one species into that of another, of related species into related species, more remote into more remote, and finally even from animals into man. The further apart the two species are, the more different are the physiological [pg 100] characters of the blood, and the more difficult does a mingling of the two become. Blood of a too distantly related form does not unite with that of the animal into which it is transfused, but the red corpuscles of the former are destroyed by the serum of the latter, break up and are eliminated. In nearly related species or races, however, the two kinds of blood unite, as in the case of horse and ass, or of hare and rabbit. Human blood serum behaves in a hostile fashion to the blood of eel, pigeon, horse, dog, cat, and even to that of Lemuroids, or that of the more remotely related “non-anthropoid” monkey; human blood transfused from a negro into a white unites readily, as does also that of orang-utan transfused into a gibbon. But human blood also unites without any breaking-up or disturbance with the blood of a chimpanzee; from which the inference is that man is not to be placed in a separate sub-order beside the other sub-orders of the Primates, the platyrrhine and catarrhine monkeys, not even in a distinct sub order beside the catarrhines; but is to be included with them in one zoological sub-order. This classification was previously suggested by Selenka on other grounds, namely, because of the points in common in the embryonic development of the catarrhine monkeys and of man, and their common distinctiveness as contrasted with the platyrrhines.10