CHAPTER l6 



MAN AND MANKIND 



CoiHiiioii Piincipks The Special Uses of Man Race Theory 

 Breeding Systems Culture and Language Clines, Tribes and Classes 



The genetic properties of man are at once less known and 

 better known than those of any creature. On the one hand, his 

 uncontrolled breeding puts him outside the pale of experiments 

 in heredity. On the other hand, the prodigious refmements of 

 historical, cultural, linguistic and medical studies give us the most 

 exact and most prolonged account available of variation in any 

 plant or animal. And not only of variation, but of something else 

 to which we have learnt to attach great genetic importance, namely, 

 mating habit. Man therefore poses a special problem, but it is one 

 that can be resolved by applying the laws of heredity discovered 

 elsewhere and discussed in our earlier chapters. To do this we must 

 demonstrate the relations between his heredity, his mating system 

 and his variation. 



Common Principles 



The mendeHan foundations we have already glanced at. From 

 the study of pedigrees many hundreds of segregating gene differ- 

 ences have been discovered in man. These are sharp differences, 

 mostly concerned (as in Drosophila) with abnormalities or defects. 

 They are due to mutant major genes of high penetrance and 

 expressivity, of the type which conveniently show mendclian 

 se2;reo;ation. 



The chromosomes of man we have also seen something of. They 

 number 48 (Fig. 46) including an XY pair in male, an XX in the 

 female. 



Some genes in man, as we saw, are sex-linked and are therefore 

 locatable in the differential segments of X and Y. Some also are par- 

 tially sex-linked and are therefore locatable in the pairing segments 

 of X and Y (Fig. 13), a situation otherwise known only in Cukx, 

 Lebistes, Drosophila, and perhaps the cat. The rest, showing no 



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