EDITORIAL STATEMENT. V 



laws of heredity and evolution; (2) that in the study of variation it is necessary to 

 go beyond the biometrician's curve to a knowledge of "the history of the individual 

 phenomenon"; (3) that dominance is a thing of many degrees, and is far from 

 rei^resenting a natural law; (4) that in wider crosses, at least, blended inheritance 

 seems to be the more general phenomenon; (5) that very many gradations of 

 "fertiUty" exist; (6) that apparently some of the most interesting facts of devel- 

 opment can be learned only through a utilization of such known gradations of 

 fertility; (7) that males only (or almost exclusively) result from numerous crosses 

 in which fertility ("germ compatibility") is much reduced by a choice of birds 

 widely separated in the pigeon group. 



The more important conclusions of the seventh paper — the extended series of 

 short statements, not really in manuscript form — were as follows: (1) that fertility 

 ("germ compatibility" and "germ strength") in its varying degrees is closely 

 associated with the production of sex and color; (2) that fertility varies much in 

 individuals of the same species, at different ages and at different stages of the 

 season; (3) that in general the "stronger germs" arise toward the first of the 

 season and tend to produce males; the "weaker germs" produced in late summer, 

 especially by birds "overworked at reproduction," tend to produce females (and 

 more white color) ; still later there is a tendency to a production of eggs capable 

 of little or of no development; (4) that there is a predominance of males from the 

 first egg and of females from the second egg of the pigeon's clutch ;2 (5) that the 

 male goes further in development and arises from a "stronger germ" than does 

 the female; (6) that strength in the parents tends, among pigeons, to produce male 

 offspring; (7) that inbreeding in pigeons leads to the production of weaker germs; 

 (8) that immaturity and old age in pigeons are also associated with the production 

 of weaker germs; (9) that white color, albinism, and color "mutations" may arise, 

 by quantitative variation, from the weak germs incident to inbreeding, old age, 

 and lateness of season; and that such quantitative variations ("mutations") are 

 proved to be of genetic value; and, furthermore, that with pigeons, by simple 

 known means, one should be able progressively to shift the "strength" of their 

 germs so as to secure either a greater or a smaller number of these "mutations." ^ 

 In other words. Whitman's later studies constitute a discovery and a partial analy- 

 sis of certain means of so modifying the germ-plasm as to carry it from one develop- 

 mental and hereditary capacity to another; and in the light of these results to 

 affirm continuity, quantitativeness, and fluidity regarding the bases of the heredi- 

 tary characters in question — ^fertility, sex, and color. This, too, at a time when 

 very many of his fellow biologists have, in large measure, been closely committed 

 to the view that discontinuity, qualitativeness, and fixity are the essential bases 

 of hereditary ]3henomena. 



These latter interpretations are, of course, currently thought to be especially 

 well founded in connection with the heredity of sex. It is of the highest importance, 

 therefore, that sex is one of the characters which has apparently been thus approxi- 

 mately brought under control. 



"rhis is true for many "pure (wild) species"; see a further statement at the close of Chapter XIII. 

 'A more complete consideration of "mutations" is given in Volume I. They are treated in the present volume 

 only in so far as they are one — a rather infrequent one — of the several phenomena exhibited by "weak germs." 



