TOPICS IN INHERITANCE. 97 



V SEX IN HYBRIDS. 



There is a widely held and frequently expressed opinion that hybrids show 

 an excessive proportion of males. Bateson and Saunders (1902, p. 139) 

 probably have this in mind in their statement " the statistical distribution 

 of sex among first crosses shows great departure from the normal propor- 

 tions." I have therefore been interested to tabulate the sex proportions 

 in my hybrids. Without giving the full table, I may state that the totals 

 are : Males, 204 ; females, 173 ; sex undetermined, 573. There is here an 

 excess of males ; but in view of the large early death rate, this may well be 

 due to a difference in the death rate of the two sexes. Taking the different 

 series of hybrids separately, most of them gave an approximation to equality 

 of the sexes. One of the most striking departures is the series of Dark 

 Brahma (121 9) X Tosa (8A J") hybrids. Of 22 individuals that developed 

 to 1 8 days in the incubator, all but one grew to maturity. Of these 21, 1 6 

 are males and 5 females. The first egg laid by the Dark Brahma after she 

 was put with the Tosa fowl developed into a female ; the next nine that 

 hatched were males ; also her last six young were males. The exceptions / 

 to the law of equality of sexes in hybrid offspring are thus individual and - 

 not of general significance. 



CORRELATION OF CHARACTERISTICS. 



Every taxonomic description testifies to the fact that a certain set of 

 characteristics is usually found associated in each species or variety. The 

 prevailing theory has been that this association is a necessary one, maintained 

 because all the characters are necessary to the success of the species in its 

 relations to external environment, or else that they were physiologically inter- 

 dependent. Modern work in hybridizing is establishing the fact that few of I 

 the specific characteristics are interdependent. Their association is, so far 

 as interaction goes, mostly accidental. Thus in my experiments with poultry 

 I have merely reached the same conclusions as have been gained by Johannsen 

 (1899, P- 185), de Vries (1903, p. 494), and indeed all recent workers. I 

 find, namely, that of the scores of evident external characteristics of poultry 

 that are inherited in alternative fashion scarcely two can be found that are 

 always associated. The most striking exception is the association of high 

 nostril and absence of single comb. 



What, then, is the meaning of correlation in nature? Clearly it is only 

 rarely due to physiological interdependence. It may often be due to an 

 unrelated association of characters independently advantageous to the organ- 

 ism. It is doubtless due to an accidental association of characters brought 

 into the race by successive mutations or by hybridizations and never disturbed, 

 because not prejudicial to the well-being of the species. 



