6 SEX AND HEREDITY 



that increase in numbers was not in the first instance 

 an essential consequence of sex. In the very simplest 

 Animals and Plants sex involves an actual decrease in 

 number. Where the whole organism consists of only a 

 single cell, and two such individuals fuse sexually to form 

 one zygote, obviously the immediate result is a fall in 

 number to one half. So we must seek some other initial 

 reason for sex than increase in number. Many believe 

 that in the first instance the advantage following from 

 sexual fusion lay in nutrition. The two gametes fused 

 together form a stronger cell than either of them was 

 alone. It seems natural then to conclude that in uni- 

 cellular organisms sexuality may have originated in the 

 nutritional advantage that followed on their fusion. 



But with this fusion there follows as a consequence 

 the pooling of such qualities as the fusing cells them- 

 selves possess. So far as these qualities can be trans- 

 mitted to the offspring, the mechanism of fusion offers 

 the opportunity for their transmission. And we do 

 positively know that the general characteristics of the 

 parents, and even many quite trivial peculiarities, are 

 liable to be transmitted to the offspring. Any human 

 family gives evidence of this. What is seen in Man 

 appears also in Animals and Plants, as every breeder of 

 prize stock and every horticulturalist knows. There is 

 no doubt whatever that Heredity is a fact. But the 

 chances that the sexually produced offspring will exactly 

 repeat all the characters of either parent are extremely 

 remote. It shares the characters of both parents, but practi- 

 cally in all cases it differs in some degree from each of them. 



Whether produced, as in very simple creatures, by 

 direct fission, or as in more advanced organisms by 

 budding, or through sexual fusion, the progeny is always 



