HUMAN GENETICS 35I 



services, differential mortality no longer plays the main part in altering 

 the proportions of different genotypes from generation to generation in 

 races fairly well adapted to their enviromiients, such as the Western 

 Europeans. Rare deleterious genes are, of course, still being eliminated, 

 more rapidly if they are dominants, very slowly if they are recessives. 

 In races recently brought into contact with new death-dealing agencies, 

 for instance, in savage races newly introduced to tuberculosis and 

 alcohol, natural selection for resistance probably proceeds with great 

 vigour through the higher death-rate of susceptible individuals. Some 

 savage races, such as the Polynesians and Maori, were reduced to a 

 small fraction of their original numbers in the first years of contact with 

 white culture, but now seem to be increasing again. But it is not clear 

 whether this is because the more resistant stocks have been selected 

 or whether it is a result of gradual ameUoration of the culture contact; 

 civihzation which at first appeared in the guise of guns, traders, and 

 alcohol, becomes in time a matter of medical stations and labour laws. 



In European and American populations, the main evolutionary 

 changes are brought about by the differential birth-rates, or better the 

 different Malthusian parameters (p. 288) of the nations and classes. 

 Unfortimately, the Malthusian parameters, or net reproductive rates 

 (number of children per mother, correaed for death-rates and age 

 composition), are only available for European nations and North 

 America.^ The most industrialized of these nations are failing to main- 

 tain their populations, having net reproductive rates of less than i, 

 while in others the rate is sinking and will probably soon be below 

 imity. Special efforts have been made in Germany and Italy to en- 

 courage fertility, but it appears that the success which was at first 

 obtained was only temporary. Of countries with a high reproductive 

 rate, Russia is the main example in Europe; in 1927 the net reproduc- 

 tive rate in the European parts of the country was about i • 7, slightly 

 more than double that of England and Wales. In other parts of the 

 v/orld, Japan is probably the country with the highest net reproductive 

 rate, but only rough statistics are available; some students profess to dis- 

 cern the beginning of a reduction in Japanese fertility and foretell a fairly 

 rapid approach to the conditions found in other industrialized countries. 



The differential reproduction of different nations is a problem better 

 treated from a political and social point of view than from a purely 

 genetical one.^ 



^ Charles 1934, Lorimer and Osborn 1934. 



2 For further discussioiij see Duncan 1929, Thompson 1935. 



