126 HEREDITARY CHARACTERS 



that individual variations may be represented in individual 

 chromosomes must be wrong. Not only can this preser- 

 vation be explained, but the explanation provides for that 

 elimination of variations which is so obvious in evolution 

 and is but inadequately provided for by natural selection 

 alone. Natural selection explains the elimination of indi- 

 viduals that vary in unfavourable directions. We know, 

 however, that variations occur constantly in all directions, 

 and some though not unfavourable, are not definitely 

 favourable. We ought therefore, under the action of 

 natural selection alone, to find races overloaded with 

 useless variations and even greater and more sharply 

 defined differences within species and races than we do, for 

 a very few generations would tend to produce individuals 

 with new and very divergent but useless characters. As a 

 matter of fact, however, we find that, under natural con- 

 ditions in spite of individual variations, the mean of the 

 race remains the same, that individual characters are few 

 in comparison with racial characters, and that the acqui- 

 sition of new racial characters is a very lengthy process 

 indeed. How then does the hypothesis of individual, 

 chromosomes being the bearers of individual variations 

 work out with the theory of natural selection ? In formu- 

 lating the proposition it was allowed in the case of man 

 that the cells of the two parents might possibly contain 

 thirty-two similar chromosomes. Though possible, this is 

 extraordinarily improbable, for the parental cells in turn 

 derived their chromosomes in a manner similar to those of 

 the offspring, and a similar process of mixing was gone 

 through. It is therefore very probable that the same 

 character might be represented in several, even in many 

 chromosomes. If the character gave the possessor an 

 advantage, it would come under the influence of natural 

 selection, and he would have a proportionately better 

 chance of rearing offspring. His offspring would stand a 

 better chance of possessing the character than those of 

 other parents that had it not. 



