The science of life : fully illustrated in tone and line and including many diagrams

BOOK 3

chimpanzee’s blood, less with a baboon or an organ-grinder’s monkey, still less with a South American spider-monkey, but next to nothing with any animal from other mammal groups.

Occasionally anatomy gives a dubious verdict ; and then the blood-test may throw fresh light. The whales, for instance, have points of resemblance both to carnivores and to ungulates, and anatomists have hesitated between the two alternatives. Blood-tests seem to show that they are more akin to the ungulates—a valuable classificatory indication. We have spoken so far only of animals ; but antibodies are produced equally as well against plant-proteins, and the method can be, and has been, successfully used with plants. The rabbit can be injected with an extract of some plant tissue, and its blood later mixed with similar extracts from other plants. The results, from plants equally with animals, can be summed up in a sentence: likeness of chemical plan goes hand-in-hand with likeness in anatomical plan. Likeness is intrinsic and touches every aspect of the living thing. Living things resemble or differ from each other in thread and texture as in plan and form. This falls in with the idea of Evolution, but it is reasonless on any other assumption.

§ 2 Vestiges : the Evidence of the Useless

There are certain facts of anatomy which have proved not merely difficult, but impossible to explain on any other assumption than that of Evolution. These are what are called vestiges—organs which are useless to their possessor, but resemble and corre-

THE SCIENCE -OF LIFE

CHAPTER 3

spond to useful organs in other creatures. Such organs are often loosely called rudimentary organs ; however, since they seem definitely not to be the beginnings of something better, but rather to represent the ruins of past usefulness, it is better to style them vestigial.

Perhaps the most striking vestigial organs are the legs of whales. Whales have, in their flippers, well-developed fore-limbs ; but externally they show no trace of hindlimbs. However, if they are dissected, one or two little bones are to be found embedded in the flesh in the region of the hind-limb. In some whales, a pair of long rods is all that remains, representing the vestige of the limb-skeleton, while the limb is altogether gone; in others, the vestige of the hipgirdle has a vestige of a thigh-bone attached. These bones are wholly useless—there is no trace of limbs for them to support, and they have not been turned to other uses. If we believe in the special creation of each kind of whale, or even of whales as a group, we must confess that these limb-vestiges spell nonsense. But if whales have evolved from land mammals, their presence is not only natural but full of significance. Leviathan we realize is not a perfect, immaculate whale, made as a whale and as nothing else, but the descendant of a land animal doing its best to swim.

Very similar vestiges of limbs are found in some snakes. No snake has any trace of a fore-limb, and most lack hind-limbs, too. But in the boas, pythons, and one or two others, vestiges of hip-girdle and hind-limbs are to be found. Sometimes these seem to be wholly useless, while in other cases, although they have no use as limbs, they protrude as two claws, which doubtless serve some new if minor function. If,

Fig. 134. The outline and skeleton of a Greenland Right Whale. It has no hind-fin, but the useless remains of a limb-skeleton show that it is descended from four-footed creatures.

Below, the vestiges are drawn enlarged. attached to its tip.

Nole also the skeleton of the five fingers concealed within the flipper 5

A VestigialjLeg.

(P), (i), parts of the hip-girdle ; (f), thigh-bone with a vestige of the lower leg

the huge jaws carrying whalebone

plates ; and the tail, set horizontally instead of vertically as in a fish.

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