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

BOOK 3

CHAPTER 5

Tot EVOLUTION OF MAN

§ 1. Man: a Vertebrate; a Mammal ; a Primate. é Body: a Museum of Evolution. § 4. Man’s Place in Time.

§ 1 a Vertebrate ; a Primate

Man : a Mammal ;

HERE is no need to stress the physical

likeness of the higher apes, chimpanzees, gorillas, or orang-outangs to ourselves. The crowds which gather round their cages in the Zoo are a testimony to this resemblance and the interest which it inspires. Nor is the likeness one of physical structure only : we have but to watch a mother orang with her child, or a young chimpanzee at play, to realize how deep the similarity of behaviour goes. The mother dandles her baby in her arms, kisses it, strokes its head ; her gestures and the play of expression on her face have an often pathetic likeness to a human mother’s.

But it is perhaps not often realized how extremely close the resemblance is, and how, if a Martian scientist, with no personal prejudice on the subject, had been given the task of classifying the animal inhabitants of our planet, he would at once have put man in the same small group as the tailless apes with the same lack of hesitation with which he would have classified the hive-bee and the solitary bee together; and how quite unintelligible he would have found the long failure of human naturalists to take this step, and the storm of protest which arose when at last a few bold and logical spirits dared to take the objective view of man’s place in Nature.

The closeness of our likeness to the apes may best be realized by measuring it against our likeness to other vertebrates. Take a man’s body and compare it with a frog’s. A man is really very like a frog in the general plan of construction: both have internal skeletons made of bone; a spinal cord running along the back, enclosed in the backbone’s tunnel; brain in a brainbox ; eyes, ears, nose, mouth, and teeth in the same general relation ; two pairs of limbs, with skeleton corresponding almost bone for bone; and a close resemblance in the plan of their internal anatomy. Their chemical arrangements, too, are quite alike. Both have livers which break up

§ 2. Fossil Men. § 3. Man’s

amino-acids and store sugars as glycogen ; both have a pancreas which secretes trypsin ; the adrenalin manufactured by the frog’s adrenal glands is not only like but chemically identical with the product of the adrenal glands of man.

In these and scores of other ways a man is not only like a frog, but unlike the vast majority of animal types. The man-frog plan of structure and working is definitely unlike that of a cuttlefish, or an ant, or a crab, or a leech, or a sea-urchin. In zoological terms, men and frogs are vertebrates, and these other animals are not.

On the other hand, if we draw a few other vertebrates into our comparison, we see at once that there are degrees in their likeness. Man is more like a frog than a fish, for frog and man both possess lungs and fingered limbs, and a fish does not. But man is less like a frog than a dog, for man and dog have both hair, and divided hearts, and warm blood, and teeth of several different sorts, and milk, and young that are nourished in the womb ; and frogs have none of these things. In terms of classification, men and dogs are mammals, frogs are not.

But, again, a man is less like a dog than a chimpanzee. For man and chimpanzee have nails, not claws, and grasping hands with the thumb opposable to the rest of the fingers, and limbs for walking and climbing ; they have no tail ; their females have monthly periods and a single pair of breasts ; their brains are large and deeply furrowed and convoluted. And in all these ways and many others, notably in their teeth, they differ from dogs. In zoological terms, men and apes are primates, dogs are carnivores. But the resemblance between man and chimpanzee is much closer than these facts alone would indicate. We have already seen how close is their invisible, chemical resemblance. Then the visible resemblance permeates every detail of their anatomy. Their skeletons are not merely alike in general plan, but correspond actually bone by bone; the grinding teeth are extremely similar in pattern; the ape’s hands and

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