§6 HUMAN BIOLOGY 



14. Miocene: varied anthropoids, including some with 

 pre-human patterns of the molar teeth. 



15. Pliocene: probable emergence of "tertiary man." 

 V. Psychozoic ("Age of Man") 



16. Pleistocene: primitive man; beginnings of modernized 

 man. 



17. Recent: civihzed man. 



It is true that there are larger or smaller gaps between 

 each of these stages in the present imperfect state of our 

 knowledge, but within each large group there is a wide 

 range of variation in particular structures, some recalling 

 the previous stage, others prophetic of later stages. It is 

 only the few fortunate!}^ situated persons who have spent 

 years in handhng and studying the original materials all 

 along the hne from ostracoderms to man, who are in a 

 position to appreciate fully the weight of this concordant 

 testimony of systematic zoology, comparative anatomy 

 and palaeontology as to the evolution of man; but even 

 the young student of biology quickly reahzes the significance 

 of the famous blood-relationship tests and of the embryo- 

 logical proof that man resembles other mammals in the basic 

 features of his development and in his subjection to the laws 

 of heredity. 



man's debt to the earliest organisms 



As a citizen of the terrestrial biota man inherits all the 

 rights and privileges but also the responsibihties and 

 Habilities of his status. The body of man, as a mass of water, 

 of frothy protoplasm and protoplasmic by-products, is a 

 labile, combustible mixture, a chemical engine, generating 

 the power by means of which man makes a place for himself 

 in the world of hfe (Martin). Obviously this engine must 

 be more or less regularly suppHed with water, oxygen, 

 nitrogen, carbon and other well-known staples. Hence 

 perhaps the greater part of man's activity is devoted to 

 securing and consuming these necessities. Again, this chemi- 

 cal engine will work efficiently only within certain limits of 

 temperature and pressure. Hence man, like other organisms, 

 seeks those parts of the earth in which the temperatures 

 and pressures are most conducive to his welfare, and strives 



