The Theory Of Descent

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
br /> 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 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 aeons.

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 palaeontological record

itself, and so on, have been filled out with ever-increasing detail.

Palaeontology, 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 palaeontology

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 "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 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)