GENETICS m THE SERVICE OF MAN — GLASS 313 



restrictions have long existed against the closest degrees of in-mar- 

 riage. Perliaps these gi'ew up because it was commonly observed that 

 such marriages often yielded abnormal or defective children. At any 

 rate, the only practicable extension of this method would be to pro- 

 hibit marriages of first cousins, wherever now allowed. This would 

 stop only about 56 percent of all consanguineous mating, according to 

 J. B. S. Haldane, and in Baltimore, according to my own data from the 

 Baltimore Rh Laboratory, would prohibit only 5 marriages in 10,000. 

 By prohibiting assortative mating between defectives, the frequency 

 of such defects as are recessive might more readily be reduced. Thus, 

 assortative mating is strongest among the deaf, and at least two kinds 

 of deafness are inherited as simple recessives. A ban on marriage be- 

 tween deaf persons would considerably reduce hereditary deafness in 

 the population. Against this social advantage would have to be 

 weighed the counteradvantage of permitting a happy social adjust- 

 ment among the married deaf. 



Positive eugenic measures might be of two types. The more extreme 

 is the extensive use of carefully selected sires by artificial insemination, 

 as in animal breeding. It is already possible not only to transport se- 

 lected semen from one continent to another by air, and to inseminate 

 large numbers of females with it, but also to quick-freeze semen, hold 

 it indefinitely at low temperatures, and thaw it out without depriving 

 it of fertilizing power. The use that thus might be made of the semen 

 of a select male is not only worldwide but might conceivably extend 

 over several centuries of time. 



Apart from whatever social repugnance such a method would en- 

 counter, it involves a biological outcome that invites disaster. The 

 gene-sharing it promotes in the breed leads to uniformity. In animal 

 breeding this may be obviated by developing a number of individually 

 uniform, but distinct, breeds. For mankind, it is at least arguable that 

 general genetic diversity is better than uniformity. In particular, be- 

 cause of the high frequency of lethal and other harmful recessive genes 

 in the population, there is a grave danger that any widely used sire 

 might spread a detrimental gene throughout the population before it 

 was detected. This has actually happened in cattle breeding. 



The other way to promote a higher reproductive rate of the bearers 

 of desirable genes is to offer inducements and rewards for parenthood, 

 and to remove impediments to it. Such measures already have been 

 tried by many countries concerned about their decline in population, 

 rather than for any eugenic reason. Obviously, the low reproductive 

 rate of the more intelligent people is mainly a result of choice. Too 

 clearly they sec that each added child is an economic burden that di- 

 minishes the standard of living of the entire family and the oppor- 

 tunities open to the other children. As H. J. Muller once said : "It is 



