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Scientific Proceedings (ioo). 



all, is obvious — for their lethal effect would naturally eliminate at 

 once the individual possessing them were they dominant and their 

 transmission to other generations would, therefore, be impossible. 

 If we consider then the summation of characters for normal 

 development and the probability that gametes containing recessive 

 lethal factors will not be so apt to meet those of their own sort 

 in a mating with an individual of another race, as in a pure mating, 

 we have a possible explanation for the relative excess of still births 

 in pure as compared with hybrid matings. 



The ratio of sexes in the still births is as follows: 





Male. 



Female. 



Uncertain. 



Ratio. 



Pure races 



175 



161 



9 



108.69 ± 3- 8 4 



Hybrids 



29 



19 



7 



IS2.63±I2.S3 



In both these cases when the ratios are compared with the ratios 

 of Table II. it is found that the departures from the ratios there 

 obtained are probably not significant. The difference between 

 them being in the case of the hybrids 24 times its probable error 

 and in the case of the pure matings only .6 times its probable 

 error. It may, therefore, be concluded that in the material studied 

 (1) a significant excess of males is observed in the progeny of 

 human matings involving racial crosses as compared with matings 

 within the race. (2) It may be predicted that racial crosses 

 between the European races studied will produce in the first 

 hybrid generation a significant excess of males. The economic im- 

 portance of this principle to the United States is obvious, for our 

 future population will largely be formed of such hybrids. (3) 

 There are significantly fewer still births among the progeny of the 

 hybrid matings studied as compared with the pure matings. 



