No. SOU] 



EVOLUTIONARY THEORY 



461 



evolution of the race except what modifies the gerrn cells, 

 because they are all that goes from one generation to the 

 next. However, we learn little or nothing about the 

 potential traits of the germ cells by looking at these cells. 

 Our knowledge of their hereditary composition depends 

 upon the traits shown by the individuals that develop 

 out of them. We may infer the genotype by observing 

 the phenotype. But the phenotypical condition of a 

 person is a more or less imperfect index to the geno- 

 typical condition of that person. The soma is an imper- 

 fect index to the germ plasm. The difference between 

 the two schools, one asserting, the other denying the value 

 of "selection," is based primarily upon the reliance 

 placed on the sufficiency of this index. Castle says, in 

 effect, the somatic condition of my rats in respect to the 

 coat-pattern is so good an index of their germinal condi- 

 tion that whenever I select rats for a quality of the 

 pattern I am selecting them very closely for the cor- 

 responding quality of their germ plasm. Pearl says, in 

 effect, in poultry the egg-laying capacity of the hen is 

 hereditary; yet it is so poor an index of her germinal 

 idiosyncrasies in this respect that an individual with the 

 somatic characters of high laying is no more apt to have 

 the genes for high laying than an individual with the 

 somatic character of low laying. Pearl says to make 

 progress I must select for breeders those which have 

 proved their germinal quality by belonging to a race of 

 high layers. If the various sisters and daughters of the 

 hen are high layers, that is more important than the egg- 

 laying performance of the one individual, merely. 



It seems to me that the whole question is a pragmatical 

 one. If the somatic condition of a trait is a good index 

 of germinal conditions, in any case progress can be made 

 by selecting the soma in that case; if the soma is an in- 

 adequate index, then little or no progress will be made by 

 selecting the soma. We know this by breeding experi- 

 ence. If we select parents because of absence of pigment 

 in skin or eye, we select also a germ plasm devoid of the 



