MAN AND MANKIND 



continuous variation in such characters as height, pigmentation and 

 left-handedness. It enables us to present a picture of human inheri- 

 tance with nuicli firmer outhncs and in a totahty that was lacking 

 with merely mendelian examples. This is especially true since, while 

 the major gene differences are largely destructive, the polygenes 

 arc all potentially constructive in their effects, and can thus account 

 for much of the genuine diversity of man depending on 

 characteristically neutral variation. 



The independent and combined effects of the actions of chromo- 

 some breakage, major-gene mutation and polygenic recombination 

 are capable of covering a more complex pattern of variation than 

 formal mendelian statements allowed for. Monstrous births, which 

 are never advertised in any community but occur in all, are probably 

 often due to deficiencies of chromosome parts such as follow the 

 breakage of bridges observed by Koller at meiosis in man as 

 elsewhere. Unique and complex syndromes probably often have the 

 same origin. Combinations of gene mutations with other chromo- 

 some changes are difficult to demonstrate but must certainly occur. 

 Many common variations, in eye or hair colour or tongue curling, 

 for example, suggest combination of major gene with polygenic 

 effects. And finally, somatic mutation is revealed both by asymmetries 

 of shape resulting from chromosome derangements at mitosis, and 

 by flecks of colour variation, especially in the iris, resulting from 

 gene-change. 



These foundations enable us to say with confidence that the first 

 principles of genetics, depending on the determination of heredity 

 by the chromosomes, apply to man. Further, cytology agrees in 

 showing that the chromosomes actually cross-over at meiosis in 

 the normal way as the rules of inheritance suggest. And the male, the 

 sex with the higher mortality before and after birth, is the hetero- 

 zygous sex. Genetically, the two sexes differ, perhaps, much as two 

 species differ. They are mutually adapted for purposes of repro- 

 duction. But each is also adapted to its special cultural activities. 

 In these the two sexes are complementary but differently adapted 

 in different races, classes and stages of evolution, matriarchal or 

 patriarchal, monogamous or polygamous, slave or free, agricultural, 

 nomadic or predatory. 



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