EMBRYOLOGY AND EVOLUTION
that of the frogs, and finally a metanephros (or hind-kidney) like that of reptiles, birds, and mammals, which alone survives in the adult. His brain, eye, ear, in fact, all his organs, pass through stages in development that are characteristic of lower vertebrates. Even in those adult features that are distinctively human, such as the peculiar form of the hand and the foot, the number of bones in the ankle and wrist, the number of pairs of ribs, the absence of a tail and the relative hairlessness of the skin — in all these respects the human foetus resembles anthropoid apes more than adult man.
Why are not these and a hundred other structures made directly? Why this roundabout process of making a man? There is no answer but evolution.
Embryology bears indubitable testimony to the truth of evolution; ancestral history is repeated in individual history, but the record is like an ancient palimpsest that has been erased and written over again and again. Traces of the old record are still there; some are obscure, some are almost entirely obliterated, but wherever they are decipherable they, tell the old, old story of the common origin of animal and man — their similarities and their kinship.
The Causes of Development and Evolution
Ontogeny recapitulates certain stages and features of phylogeny, but the whole course of evolution through past geologic ages can be followed only by a study of fossils. The record is necessarily incomplete, for we rarely find all the stages of evolution represented in fossils. Nevertheless palaeontology is a certain guide to the general succession of living things during past ages. But evolution is a present process, going on to-day, and to see it at work it is not necessary to explore “the dark backward and abysm of time.” To be sure, it goes slowly; species are not made in a day any
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