276 THE SIGNIFICANCE OF SEXUAL EEPRODUCTION 



it follows that no individual of the second generation can be iden- 

 tical with any other. They must all differ, not only actually but 

 also potentially, for their differences exist at the very beginning of 

 development, and do not solely depend upon the accidental conditions 

 under which they live. Moreover, no one of the descendants can 

 be identical with any of the ancestors, for each of the former unites 

 within itself the hereditary tendencies of two parents, and its 

 organism is therefore, as it were, a compromise between two de- 

 velopmental tendencies. Similarly in the third generation, the 

 hereditary tendencies of two individuals of the second generation 

 enter into combination. But since the germ-plasm of the latter 

 is not simple, but composed of two individually distinct kinds of 

 germ-plasm, it follows that an individual of the third generation 

 is a compromise between four different hereditary tendencies. In 

 the fourth generation, eight ; in the fifth, sixteen ; in the sixth, 

 thirty-two different hereditary tendencies must come together, and 

 each of them will make itself more or less felt in some part of the 

 future organism. Thus by the sixth generation a large number of 

 varied combinations of ancestral individual characters will appear, 

 combinations which have never existed before and which can never 

 exist again. 



We do not know the number of generations over which the 

 specific hereditary tendencies of the first generation can make 

 themselves felt. Many facts seem to indicate however that the 

 number is large, and it is at all events greater than six. "When 

 we remember that, in the tenth generation, a single germ contains 

 1024 different germ-plasms, with their inherent hereditary ten- 

 dencies, it is quite clear that continued sexual reproduction can 

 never lead to the re-appearance of exactly the same combination, 

 but that new ones must always arise. 



New combinations are all the more probable because the different 

 idioplasms composing the germ-plasm in the germ-cells of any 

 individual are present in different degrees of intensity at different 

 times of its life ; in other words, the intensity of the component 

 idioplasms is a function of time. This conclusion follows from the 

 fact that children of the same parents are never exactly identical. 

 In one child the characters of the father may predominate, in 

 another those of the mother, in another again those of either 

 grand-parent or great-grand-parent. 



