MAN'S PLACE IN NATURE 



453 



FIG. 280. Young chimpanzee. (From Welt- 

 all u. Menschheit; after photograph from 

 life by Dr. Heck of Berlin.) 



ly derived from a common 

 stock, and each species in 

 its ramifications modified 

 by the forces and condi- 

 tions included under the 

 general heads of variation, 

 heredity, segregation, selec- 

 tion, and the impact of 

 environment precisely as 

 species in other groups are 

 affected. It is clear that if 

 there is an origin of species 

 through natural causes 

 among the lower animals 

 and plants, there is an 

 origin of species among 

 men. If homology among 

 animals and plants is the 

 stamp of blood relation- 

 ship, the same rule holds 

 with man as well. Man is connected with the lower animals 

 by the most perfect of homologies. These are traceable in 

 every bone and muscle, in every blood vessel and gland, in 



every phase of structure, 

 even including those of 

 the brain and nervous 

 system. The common 

 heredity of man with other 

 vertebrate animals is as 

 well established as any fact 

 in phylogeny can be. 



In working out the 

 details of the origin of 

 man, we have once more 

 the three "ancestral docu- 

 ments " of biology, compar- 

 ative anatomy, embryol- 

 ogy, and paleontology. 

 Considered structur- 



FIG. 281. Foot skeleton of chimpanzee at left, a ^ V ' man forms 

 and of man at right. (After Wiedersheim.) 



30 



genus, Homo, the Sole 



