ALTERNATION AND BLENDING 149 



therefore, Professer Karl Pearson is right in declaring that " Varia- 

 bility is not a product of bi-parental inheritance ; . . . whatever be 

 the physiological function of sex in evolution, it is not the 

 production of greater variability." l 



246. At the present day I think most biologists who have 

 given any thought to the question believe that the function of sex 

 is (through the mixing of germ-plasms) to mix the parental 

 qualities. There are, however, great differences of opinion as to the 

 nature and effect of this mixing. Suppose a man with black eyes 

 and six digits on each hand mates with a woman with blue eyes 

 and the normal number of digits ; then experience demonstrates that 

 each of the descendants of such a pair will have black eyes or blue 

 eyes (or perhaps grey or hazel eyes, as in some ancestor) : never, 

 or hardly ever, eyes that are intermediate ; and six digits or five 

 digits, not five and a half digits. But one or more of the children 

 may develop the father's eyes in combination with the mother's 

 hands, or the mother's eyes with the father's hands. In such a 

 child the parental characters are mixed ; but they are mixed as 

 black and blue marbles in a bag, not as black and blue colours 

 are blended on a painter's palate. On the other hand, the offspring 

 of a white man and a negress actually does blend the parental skin 

 colours ; the descendants are not black or white, but of a colour 

 that is more or less intermediate. 



247. Here, then, we have two distinct types of ' inheritance,' the 

 alternative and the blended, both of which undoubtedly occur. 

 Since in the first type the father's or the mother's character is 

 reproduced, not a blend, and since the grandchild may have patent 

 the character which was latent in the parents, the resemblance to 

 the method by which the sexual characters are * transmitted ' is 

 evident, the main difference being due to the fact that whereas the 

 various sexual characters tend strongly to hang together in distinct 

 patent or latent sets, the non-sexual characters, the reproduction 

 of which is alternative, tend to mix and so form new combinations. 

 Now the question we shall have to decide is whether the function 



1 Grammar of Science, pp. 473-4, ed. 1900. In my Work, The Principles of 

 Heredity (p. 49), I controverted Professor Pearson's statement, and pointed out 

 that a mulatto, for instance, the offspring of a white man and black woman, 

 varies from both parents in a definite way. I must now confess that I seem 

 to have mistaken Pearson's meaning. Conjugation is certainly a cause of some 

 variations, in that the offspring when they blend parental characters vary from 

 both; parents. But variations and variability are different things. A partheno- 

 genetic species may be as variable or more variable than one the reproduction 

 of which is bi-parental. 



