CHAPTER III 



Differentiation of cells Inborn and acquired characters Mental characters in 

 man Physical characters Instinct Lamarck's theory The Darwin- 

 Wallace theory Weismann's theory Oscar Hertwig's theory. 



THE following inquiry into evolution, variation, and bi- 

 parental reproduction may appear to travel wide of our 

 main object heredity. It must be remembered, however, 

 that man is essentially a wild and not a domesticated 

 species. All the various conditions under which he lives 

 have been produced by himself and not for him by some 

 other species which has interfered with natural selection. 

 It is therefore most necessary that in studying heredity we 

 should study the action of natural selection and the material 

 it works upon, and at the same time inquire with the greatest 

 care into the extent to which a comparison between the 

 phenomenon of heredity in domesticated races, and in races 

 under natural conditions, may be made with safety. 



Heredity, according to Herbert Spencer, is " the capacity 

 of every plant and animal to produce other individuals of a 

 like kind." We have seen how it is that substance derived 

 from both parents is conveyed to every cell included in the 

 multicellular organism. The cells included in the body of 

 an organism differ among themselves, but the varying 

 groups are arranged in a similar manner in organisms of 

 the same kind. In different organisms, however, the cells 

 and groups of cells differ in their arrangement and form, in 

 their function, and in the phenomena they exhibit. The 

 fertilised ovum of a dog will produce similar cells arranged 

 in similar groups, and performing the same functions as 

 those forming the bodies that produced the sperm and 

 ovum. The characters of the new individual will in fact 

 be similar to the characters of the parents. 



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