HEREDITY AND EVOLUTION 109 



of the appearance of rational power in man. All that 

 is here urged is, that similarities do not explain differ 

 ences ; and the closer the similarity in the gerrn-cell 

 and in embryonic structure, the worse the difficulty. 

 After we have gathered our illustrations of the law that 

 like produces like, there remains the question of the 

 origin of species, and specially the appearance of man. 

 As before, in judging of the hypothesis concerning 

 heredity, we had to pass forward to the evidence 

 gathered by naturalists from the life of animals in 

 their native resorts, so now we must pass over to the 

 mature normal life of man, and specially to our know 

 ledge of the facts of family history, including diversity 

 of gifts. We agree that varieties appear in mental 

 faculties, as well as in bodily structure ; and we seek 

 to know whether variations in mental faculty are 

 transmitted by mere unfolding of the fertilised germ- 

 cell. Comparative biologists, because of their sphere 

 of research, become engrossed in the life-history of 

 the germ-cell, and they naturally assume that the 

 complete life of the species, mental as well as physical, 

 is thus provided for. Nevertheless, Darwin, with 

 other observers generally, recognises a two-fold aspect 

 of human life. He affirms Man is variable in body 

 and in mind. He thus indicates that there are two 

 distinct classes of facts, and, therefore, two problems, 

 affecting human life. These two separate problems 

 certainly do not emerge in our study of cell-life, and 

 do not appear at all, in tracing the stages of develop 

 ment for organic life. What must be said as to 

 animal intelligence will come up for separate con 

 sideration by-and-by. It is admitted, as to human 

 1 Descent, p. 47. 



