202 RAYMOND PEARL AND MAUD DEWITT PEARL. 



more pronounced the results found in their absence. It appears 

 highly probable on general grounds that if still-births are not 

 proportionately distributed among cross and pure matings there 

 is somewhat more likely to be an excess of such births arising 

 from cross {i. e., according to {c)) than from pure matings {i. e., 

 according to (b)). It is hardly conceivable that there could be a 

 steady tendency for a sensibly greater number of still-births to 

 occur when both parents are of the same nationality than when 

 they are of different nationalities. If this be granted then it 

 must also be granted that the non-inclusion of still-births in the 

 present statistics cannot be adduced as an explanation of the 

 observed preponderence of males in the offspring of cross 

 matings. 



3. That a different age distribution of the parents in cross as 

 compared with pure matings may account for the observed pre- 

 ponderance of male births from such matings. In a population 

 such as that here dealt with it is undoubtedly true that the males 

 in the cross matings (being for the most part probably immi- 

 grants) are on the average somewhat older than those in the pure 

 matings. It might conceivably be contended that this greater 

 average age of the male parent was the cause of the excessive 

 production of male offspring in the cross matings. To make such 

 a contention, however, would simply be to affirm belief in Sadler's 

 "law" ^ or some variant of it which holds that the relative age 

 of the parents is causally related to the sex-ratio of the offspring. 

 In regard to this matter it need only be said that Sadler's theory 

 has been abandoned by all recent students (both from the bio- 

 logical and from the demographic side) of the problem of sex 

 simply for the reason that nothing remotely approaching conclu- 

 sive evidence has ever been brought forward in its support. 



4. That the individuals in the cross mating are exposed to 

 environmental influences different on the average from those act- 

 ing on the individuals in pure matings and that the differences in 

 the sex-ratios of the offspring of these two groups are the result 

 of these environmental differences. This possible explanation 

 obviously needs careful consideration. So far as broad environ- 



' Cf. Geddes and Thomson, " The Evolution of Sex " or any of the standard works 

 on vital statistics for an account of this law. 



