HUMAN GENETICS 355 



man race theory, which allows a popular ideal to be stated in terms 

 which can be shown to be without scientific foundation; and this basis 

 could scarcely be removed without causing some alteration in the 

 superstructure. Similarly, a geneticist would, surely, fail in his duty if 

 he did not question any judgment based on the supposition that all men 

 are bom equal. A student of human genetics must perforce train him- 

 self to eliminate from just these judgments all the elements of irra- 

 tionaUty which render most human opinions so fallible; about the 

 subject of his own study, he, if anybody, should be able to give an 

 objective and unbiassed assessment of value. If he observes the ordinary 

 rules of scientific thought, he is likely to err if anything on the side of 

 excessive caution rather than of wanton interference with human 

 behaviour. 



The genetic composition of the population could be improved either 

 by lowering the fertiUty of the carriers of deleterious genes or raising 

 that of the carriers of favourable ones. Of the methods of lowering 

 fertility, sterihzation is the most radical, and since, if breeding is to be 

 discouraged, it might as well, in most cases, be prevented altogether, 

 it is probably the most generally useful.^ Naturally, such a procedure 

 should not be applied except to individuals who are known to carry 

 genes whose harmful effects are generally acknowledged; instances 

 would be the hereditary absence of both arms and legs, amaurotic 

 family idiocy, etc., which everyone would agree to be undesirable. The 

 operation of sterilization has no effects other than rendering the oper- 

 ated individual sterile. The technique generally employed is severing 

 the genital ducts, the vas deferens in the male, the fallopian tubes in 

 the female. Sexual drive and potency remain normal. 



The effect on the population is to eUminate a source from which the 

 unwanted genes can be perpetuated. The phenotypic effect, of course, 

 depends primarily on the mode of inheritance of the gene, since it is 

 only possible to sterilize the individuals in which the gene is manifest. 

 Dominants could therefore be eradicated in one generation, except in 

 so far as they are renewed by mutation. Similarly, sex-linked recessives 

 could be eliminated fairly rapidly since all the male carriers would 

 show the presence of the gene. Haldane^ has discussed the case of 

 haemophilia, a sex-linked recessive which causes a failure of the blood 

 to clot, so that affected males usually die young from trivial wounds 

 and fail to reproduce themselves. Since the frequency of the haemo- 



^ For discussion, see Haldane 1938, Hogben 193 1, Holmes 1934, Popenhoe 

 and Johnson 1933. ^ Haldane 1935. 



