Many examples might be cited of man coming by distinctive characters by retaining foetal states, but the following may be taken as representative. In all foetal primates the brain is rela tively large and the jaws absolutely small; this is certainly not an ancestral state, for in all the older forms of primate the brain is small and the jaws large. Man is distinguished by the large size of his brain and the relatively small size of his teeth and jaws. How he compares with adults of great anthropoid apes may be seen from the following data. We may take the capacity of the cranial cavity to represent the size of brain and the area of the palate to represent the size of the jaws. In a well-grown adult European male we expect a cranial capacity of 1,500 c.c. and a palatal area of 25 sq. cm., there being 6o c.c. of brain space for every square centimetre of palate. The average male gorilla has a cranial capacity of 470 c.c., a palatal area of 72 sq. cm., that is, 5.8 c.c. of brain space for every square centimetre of palate. The corresponding figures for the average male orang are : 412 c.c., 62 sq. cm., giving a cranio-palatal ratio 6.6:i; in the average male chimpanzee the figures are: 390 c.c., 46 sq. cm., giving a ratio of 8.5:1. There is a wide gap between the European cranio-palatal ratio 6o : I and that of the chimpanzee, 8.5 :1. We may fill the gap somewhat by citing a Tasmanian skull with a capacity of 1,35o c.c., a palatal area of 36.7 sq. cm. and a ratio of 36.7:I.
We find a still nearer approach to the anthropoid condition in the fossil skull of Rhodesian man in which the cranial capacity is 1,300 c.c., the palatal area 41 sq. cm., the cranio-palatal ratio 31.7:1. Even this ratio is far above that of the chimpanzee, 8.5 :i; but if we take a suckling chimpanzee, in which the cranial capac ity is 26o c.c. and the area of palate 13.6 sq. cm., we obtain a ratio 19:1, an approach to the human proportion. If we take a still earlier stage, such as may be observed in a chimpanzee foetus during the eighth month of development, we find a ratio which is human in its magnitude. Man has come by his small palate by retaining a foetal anthropoid condition, and this is true of all the parts of man's skull which are concerned in mas tication. This tendency to foetal inheritance is not confined to
the human branch of primates; in certain genera of New World monkeys, particularly in Chrysothrix and Cebus, we see in their small jaws and large heads the same law at work.
The belief that many of man's foetal characters do not reflect ancestral stages, but foreshadow the trend of future evolution, was held by several anatomists in Germany towards the end of the 19th century, particularly by Ranke. The law of foetal in heritance, so far as it relates to man, has been greatly extended during recent years in a series of papers by Prof. L. Bolk of Amsterdam (Proc. of the Roy. Acad. of Sc. of Amsterdam, 1921– 5). Embryological evidence, if it has failed to reveal the pithe coid states through which man has passed in his ascent, does provide conclusive evidence of his simian ancestry. In the de velopment of his brain, for example, we see that the first fissures to appear are those which occur in the brains of the higher monkeys ; the next are those which are found in the brains of the great anthropoids, and later still the secondary human sulci are formed; but never at any stage does the human brain corre spond. to that of monkey or of anthropoid. If embryology has failed to reveal the details of man's history, it has shown that the processes of evolution are at work on the foetal body; if the study of the foetus does not help us to decipher man's past, it does seem to provide a basis on which we may forecast the future of the human body. The brain of the gorilla, in the totality of its characters, is the most like that of man ; these two are struc tural allies, yet evolution has moulded their bodies in opposite directions. During growth the gorilla replaces all its f oetal characters by those of brutality and strength; in man the tend ency has been to retain the delicate physique of the young and to shed those of a more brutal nature. Why the one fate over took the gorilla and another fell to man remains an enigma.