EVOLUTION 263 



not, can not, become Hawaiians, even though there might be some en- 

 vironmental convergence. 



We now regard human races as much more plastic than we formerly 

 did. But our concept of plasticity is basically a genetic one. There are a 

 multitude of genes which encompass the entire range of human physical 

 characters. Plasticity resides principally in recombinations of these char- 

 acters. Recently Mills ^- has shown that there is another phase to this 

 plasticity, an environment (diatetic) aspect. He found that vitamin B re- 

 quirements (thiamin, pantothenic acid, and pyroxidene at least) are much 

 higher in the tropic than in a temperate zone and that growth and de- 

 velopment are inhibited by inadequate B intake under tropical living 

 conditions. Here is an example where growth-pattern and hence adult con- 

 figuration (taken as a racial criterion) is modifiable by the food environ- 

 ment. We are just beginning to learn how a temperate-zone White man 

 may possibly adjust to a subtropical or tropical habitat, but for one fact 

 we know there are 100 questions that are still to be answered. 



The fifth "don't" is found in the functional aspects of Man: we know 

 little about the physiology of race-types. We have studied racial metabo- 

 lism, pulse-rate, respiration-rate, and so on, but these analyses are not so 

 much tests of race-groups per se as reflections of conditions under which 

 they live. There is no reason, really, to assume difference in kind, rather 

 only differences in degree. If we relate body-type to body-function then 

 distinct group differences can not be expected, for body-type cuts across 

 stock- and race-lines. ^^ 



There is another phase of the functional problem which requires clas- 

 sification, viz., so-called "racial susceptibilities." For example, the peoples 

 of North Europe are said to be prone to whooping cough, resistant to 

 goiter and cretinism; the peoples of Central Europe fall prey to goiter 

 and cretinism, but withstand pulmonary diseases; the American Negro 

 succumbs to tuberculosis, diseases of heart, lungs and kidneys, and more 

 successfully combats malaria, yellow fever, measles, scarlet fever and 

 diphtheria.^^ Are these really racial difi^erences? Probably not. The answer 

 is more likely to be found in problems of relative isolation and exposure, 

 and most certainly in considerations of socio-economic standards. There 

 are, so far as we know, no genetico-racial biological differences in the 

 organs which will conduct to, or inhibit, organic breakdown under the 

 onslaught of disease. The problem, however, is still one to be explored. 



The sixth and final "don't" is that we do not know of any characteristics, 

 either biological or psychological, that in a given race-cross are superior 



12 C. A. Mills, "Climatic Effects on Growth and Development, with Particular Ref- 

 erence to the Effects of Tropical Residence," Avier. Anthropol., 44: 1-13. 1942. 



13 F. Weidenreich, "Rasse und Korperbau," Springer, Berlin, 1927. 



1* A. Hrdlicka, "Immunity as the Chief Task of Future Aledicine," Lit. Digest, Dec. 

 9, 1933 (see p. 14); see also J. H. Lewis, "The Biology of the Negro," University of 

 Chicago Press, 1942. 



