Fetal Growth of Man and Other Primates

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Abstract
A condensed review of the literature is followed by a discussion of changes in body proportions during fetal growth of man, apes, and monkeys, based on the author''s studies on 623 white and negro fetuses and on 175 monkeys and apes ranging in age from early fetal to adult life. The rate of growth decreases in general very rapidly with advancing development but shows marked fluctuation at certain periods. Different parts of the body grow at different rates and these rates frequently alternate in adjoining parts as well as in height and width dimensions. The "law of developmental direction" exerts its influence throughout the greater part of fetal life. Mos.t of the paper is devoted to an outline of growth changes in proportions of the trunk, limbs, and head, considering such points as relative height of the shoulders, relative position of nipples and umbilicus, relative lengths of the various digits on hand and foot, shape and relative size of the nose, mouth, etc. All these features change in principle similarly in the different primates, but with advance in development the differences between man and apes or monkeys become more and more marked, fetuses resembling each other much more closely than adults. Many racial differences between adult whites and negroes are clearly defined in fetal life. Individual variations are as pronounced before birth as at maturity, and even asymmetries are found with great regularity at prenatal stages of growth. In no case did the ontogenetic changes in a given character converge, either in different human races or in different forms of primates. All human racial differences and all differences between man and apes or monkeys increase during some periods of growth and remain the same during other periods, but never become less with advancing development. This strongly supports the assumption of a monophyletic origin of the human races and of one common ancestry for all primates, from which all inherited the tendency for the same ontogenetic processes, which, in turn, could only have become modified through later specializations. The paper contains a bibliography of 172 titles.

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