NATURAL SELECTION 



FiGtTRE 89. Industrial Melanism in Lymantria monacha. Each row of three repre- 

 sents one combination of the two pairs of autosomal genes and the one pair of sex- 

 linked genes which control melanism in this species. ( From Goldschmidt, "The Material 

 Basis of Evolution," Yale University Press, 1940. ) 



but it is nonetheless common in equatorial Africa. This was inexplicable 

 until it was found that heterozygous persons are resistant to malaria, 

 which is prevalent in the same region. Thus selection favors heterozygos- 

 ity, in spite of the severe liability of homozygosity. 



The fact of the effectiveness of selection in nature, originally postulated 

 by Darwin as a necessary consequence of the prodigality of nature and 

 of the variability of all species, has been thoroughly vindicated by obser- 

 vations such as those reported above. Some special aspects of natural 



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