y8 THE EVOLUTION OF MAN 



bral column, the coccyx, which represents the tail vertebrae of 

 the lower animals, no longer projects. Very rare cases are 

 known in which the coccyx has remained elongated and pro- 

 jecting in man, thus constituting a true tail. In the anthro- 

 poid apes this region is even more reduced than in man. 



Small supernumerary mammary glands (Fig. 27), which are 

 not infrequently found in man, are reversionary structures. It 

 is found that in early embryonic life, two rows of mammary 

 glands begin to develop but, unlike the case of the lower 

 mammals, all except two of these disappear. Also, at the 

 sixth month of prenatal life, the body is almost entirely covered 

 with fine hair, called the lanugo. This is largely shed before 

 birth but, in some cases, it may persist and develop in the adult 

 to form a complete hairy covering for the body, which seems 

 to be a reversion to man's ancestral hairy condition such as 

 persists in the anthropoid apes. 



Thus man's close kinship with the anthropoid apes is 

 strongly suggested not only by the fossil forms but also by his 

 natural history. Furthermore, a 'blood relationship' is indi- 

 cated both by the susceptibility of the apes to human diseases 

 and by their reaction to various blood tests, developed in the 

 past few years, which render it possible to distinguish between 

 human blood and the blood of all other animals except the an- 

 thropoid apes. It is pretty well agreed that the anthropoid apes 

 and man came from a common ancestor, and he in turn from 

 some primitive, broad-nosed ape. Some believe that the mam- 

 mals were evolved from a primitive reptilian form. Others say 

 they came from the amphibians, which in turn evolved from a 

 fish form, the latter from an invertebrate, and so on down to 

 the protozoa. Evolution must likewise assume that under 

 some favorable condition the earliest living forms were evolved 

 from the inorganic world. Whether such a process is going 

 on at present no one knows. However, the facts of man's 

 development, structure, and variations, which have been given 



