544 



SCIENCE 



[N. S. Vol. XXXVII. No. 954 



in the body or soma. Those qualities alone 

 are inherited, which are innate in the germ 

 cells, the ova and the spermatozoa. Here 

 only can the breeder find the means with 

 which to accomplish his ends. However 

 interesting theoretically may be those rare 

 and still doubtful cases in which extraordi- 

 nary influences acting upon the body under 

 the controlled and special conditions of 

 the laboratory may perhaps influence the 

 germ cells through the soma, they have no 

 bearing on the practical conduct of the 

 breeders' craft. Genetics has demonstrated 

 that he may cast aside, for once and all, 

 that mass of tradition and superstition 

 which assumes that influences specifically 

 affecting the body will specifically modify 

 subsequent generations. Has not genetics 

 done breeding a service of great value in 

 freeing it of the sinister influence of ' ' teleg- 

 ony," "saturation," "maternal impres- 

 sions" and similar sorts of nonsense? 



(&) That specific characters or groups of 

 characters, in the great majority of cases 

 and perhaps all, are inherited as discrete 

 and definite units. If one mates a pea- 

 combed fowl with a single-combed, all 

 the offspring will have pea-combs. This 

 result occurs whether the pea-combed pa- 

 rent is a Game or a Brahma; whether it is 

 a male or a female ; whether it is a strong, 

 vigorous individual, or the sickliest, weak- 

 est scrub in the flock. In other words the 

 kind of bird it is whose germ cells carry 

 the potentiality to make pea-combs develop 

 in the offspring, so far as we now know 

 has nothing to do with the specific result 

 (i. e., the production of a pea comb, rather 

 than a single, a rose, or any other kind). 

 Comb form is inherited as a discrete unit 

 uninfluenced by the individual's other at- 

 tributes. This discovery that characters 

 are inherited as separate units — and no 

 principle of genetics is more firmly 

 grounded than this — gives the breeder a 



totally new concept of the meaning of 

 "purity" of blood in breeding. We see 

 now that properly (i. e., biologically) one 

 can only speak of an animal as being 

 "pure-bred" when he specifies the particu- 

 lar character to which he refers. A chick 

 may be the veriest mongrel in all other re- 

 spects and yet carry in the germ cells only 

 that potentiality in respect to comb form 

 which leads to the development of a pea- 

 comb. Then however much of a mongrel it 

 may be in respect to all other characters, it 

 is "pure" and "pure-bred" so far as con- 

 cerns comb. Is it not a contribution of 

 moment to the breeder to have demonstrated 

 that in his breeding operations he may 

 safely and surely deal with individual char- 

 acters, and groups of correlated characters 

 as units 1 



(c) That in a very great range of cases, 

 perhaps in all — the number of known cases 

 daily grows larger — the Mendelian law of 

 segregation and recombination of charac- 

 ters operates. In the formation of the 

 germ-cells of an individual there is a sort- 

 ing out or segregation of the hereditary 

 characteristics contributed by the father 

 and the mother and a readjustment of 

 these into all of the combinations, both 

 old and new, which are mathematically 

 possible. What may be the precise cellu- 

 lar mechanism or basis of this wonderful 

 process is not altogether certain, but the 

 phenomenon itself is as certain as the phe- 

 nomenon of gravitation. It operates as 

 well in regard to the minutest heritable 

 differences in the pedigreed specimens of 

 the same sub-breed as in the wide differ- 

 ences of true hybridization. Properly un- 

 derstood, it enables the breeder to interpret 

 and weigh the results of his breeding oper- 

 ations, and so intelligently to plan the 

 next steps with a certainty and precision 

 hitherto unattainable. Is not this a real 

 contribution of science to practise ? 



