394 HISTORY OF THEORIES 



It cannot be said that this historical retrospect leads us to 

 any complete and satisfactory interpretation of all the puzzling 

 facts which are covered by the word " heredity," but it will 

 indicate some of the main attempts which have been made, and 

 which of these are most promising. We must still recognise the 

 justice of Herbert Spencer's words : 



" A positive explanation of heredity is not to be expected 

 in the present state of biology. We can look for nothing beyond 

 a simplification of the problem, and a reduction of it to the same 

 category with certain other problems which also admit of hypo- 

 thetical solution only. If an hypothesis which certain other 

 wide-spread phenomena have already thrust upon us can be 

 shown to render the phenomena of heredity more intelligible than 

 they at present seem, we shall have reason to entertain it." * 



2. The Old Theories of Heredity 



There have been many attempts at theories of heredity and 

 inheritance, but it is not profitable to say much about the earlier 

 ones, most of which were theological or metaphysical rather 

 than scientific. It will be seen, however, that shrewd enough 

 ideas are sometimes hidden in the old theories, whose phraseology 

 no longer appeals to the scientific mind. 



(a) Theological Theories. In olden times the idea was 

 prevalent that the germ of a new human life was at conception 

 possessed by a spirit, which thereafter became responsible for 

 development. As it is not so very long ago (1760 or later) that 

 even digestion was explained as the work of a spirit, it need not 

 surprise us that development was relegated to a similar unverifi- 

 able efficiency. Sometimes the spirit was, so to speak, of second- 

 hand origin, having previously belonged to some ancestor or 

 to some animal. The idea of successive reincarnations has had 

 many expressions in the West as well as in the East. 



* Herbert Spencer, Principles of Biology, vol. i. (ist ed. 1863). 



