CHAPTER VIII 



THE CAUSE OF SPONTANEOUS VARIATIONS 



The inherent tendency to vary Galton's Law of Inheritance In-breed- 

 ing and cross-breeding Fertility and sterility The effects of 

 domestication on fertility The geographical distribution of species 

 Summary. 



160. IF spontaneous variations are not due to the trans- 

 mission of acquirements, nor to the direct action of the 

 environment on the germ-plasm, nor to bi-parental reproduc- 

 tion, to what then are they due ? Undoubtedly to an inborn 

 tendency to vary, a tendency that is inherent in the germ- 

 plasm of every species of plant and animal But whence 

 this tendency ? In the present state of our knowledge in 

 the total lack of all evidence we can only speculate vaguely. 

 To me it seems probable that, in that distant past when life 

 was near its origins, all living beings were homogeneous in 

 structure, and that they produced offspring by fission, or 

 rather fragmentation, similar to themselves ; but that, amongst 

 these homogeneous organisms, there arose beings which had 

 a tendency to be heterogeneous in structure, and the frag- 

 mentation of which therefore produced offspring that varied 

 among themselves. The question as to the steps by which 

 this departure from homogeneity was achieved is interesting, 

 but it is not material to the matter in hand. Very plainly it 

 did occur somehow. By some means or other it came about 

 that organisms produced offspring that varied spontaneously 

 amongst themselves. Possibly or probably the result was 

 brought about by the environment acting directly on the 

 individual, but affecting his different parts (e. g. outer and 

 inner parts) differently. The moment differentiation among 

 offspring occurred a great advantage in the struggle for exist- 

 ence was conferred. Natural Selection came into being and 

 evolution followed. Natural Selection could then fix two 

 vitally important laws of heredity, two hereditary tendencies 



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