12 HEREDITY AND SEX 



organism and its environment must be a very delicate 

 matter. One combination may be best suited to one 

 environment, and another combination to another. 

 ( Jonjugation brings about in a population a vast num- 

 ber of combinations, some of which may be suited to 

 the time and place where they occur. These survive 

 and produce the next generation. 



Jennings' experiments show, if I understand him 

 correctly, that the race he used was not homogeneous 

 in its hereditary elements ; for when two individuals 

 conjugated, new combinations of the elements were 

 formed. It seems probable, therefore, that the chemi- 

 cal equilibrium of paramcecium is maintained by the 

 presence of not too much of some, or too little of other, 

 hereditary materials. In a word, its favorable com- 

 binations are mixed or heterozygous. 



The meaning of conjugation, and by implication, 

 the meaning of fertilization in higher forms is from this 

 point of view as follows : - - In many forms the race, as a 

 whole, is best maintained by adapting itself to a widely 

 varied environment. A heterozygous or hybrid con- 

 stitution makes this possible, and is more likely to 

 perpetuate itself in the long run than a homozygous 

 race that is from the nature of the case suited to a more 

 limited range of external conditions. 



What bearing has this conclusion on the problem of 

 the evolution of sex and of sexual reproduction? 



This is a question that is certain to be asked. I am 

 not sure that it is wise to try to answer it at present, 

 in the first place because of the uncertainty about the 

 conclusions themselves, and in the next place, because, 

 personally, I think it very unfair and often very unfor- 



