200 INBREEDING AND OUTBREEDING 



vantage is almost incalculable. Ten variations in an 

 asexual species mean simply 10 types ; 10 variations in a 

 sexual species mean the possibility of 1024 types. Twenty 

 variations in the one case is again only 20 types to survive 

 or perish in the struggle for existence ; 20 variations, in 

 the other case, may present 1,032,576 types to compete in 

 the struggle. It is necessary to condition the argument 

 by pointing out that these figures are the maximum possi- 

 bilities in favor of sexual reproduction. It is improbable 

 that they ever actually occur in nature, for 2^^ types really 

 to be found in the wild competing for place after only 20 

 germinal variations would mean an enormous number of 

 individuals even if the 20 changes had taken place in dif- 

 ferent chromosomes, and if the variations were linked at 

 all closely in inheritance the number required would be 

 staggering. But there are breaks in linked inheritance, 

 and the possibility is as stated. Associated with this 

 benefit arising from the law of recombination, there is 

 another of great practical importance resulting from the 

 phenomenon of dominance. Recessive variations may 

 arise, which in the particular factorial complex existing 

 in the individuals at the time of origin, would cause the 

 possessors to be eliminated by natural selection. These 

 variations, however, may be carried an indefinite number 

 of generations in the heterozygous condition, thus multi- 

 plying the chances that they finally be combined with 

 other factors in complexes which as a whole are desirable. 

 These inestimable advantages remain even though it 

 should be shown later that the more fundamental and 

 generalized characters of an organism are not distributed 

 by Mendelian heredity. Loeb ^^9 suggests that the cyto- 

 plasm of the egg is roughly the potential embryo and that 



