138 EVOLUTION AND GENETICS 



Ideated over and over again, bnt sooner or later two 

 individuals each carrying the gene may mate. One- 

 fourth of their offspring will then show the new 

 character, which now appears for the first time. Sev- 

 eral or many mutant individuals w^ill then suddenly 

 emerge, and since they are the output of the same 

 female, their proximity will increase the chance that 

 two at least mate with each other and produce 

 progeny with the new character. 



These considerations are significant for the selec- 

 tion theory. They show that there is no danger of a 

 new mutant being lost at its inception, except in so 

 far as chance works against the survival of the off- 

 spring of any one individual. They show also that 

 a new gene may, by chance, become distributed in 

 the race before its character comes to the surface. If, 

 when it appears, the new character is one that better 

 fits the individuals to some environment at hand, 

 such individuals have a better chance of survival 

 and, other things being equal, of leaving offspring. 

 If one of them mates with an individual of the orig- 

 inal race the same process takes place all over again, 

 but as often as this happens, the new gene may 

 spread in the race at the expense of the old, and may 

 replace it if the character it stands for is one better 

 suited to the old environment ; or, if better fitted to 

 a new environment within reach, it will then give 

 rise to a new^ type leaving the original type in pos- 

 session of the old station. 



