SOME POSSIBLE BEARINGS OF CxENETICS ON PATHOLOGY 9 



In connection with the question of spreading of mutant genes 

 in the race there is another consideration, seldom referred to, that 

 may occasionally have some weight in accounting for the dis- 

 persal of genes. In some combinations the hybrid may be more- 

 vigorous and more fertile than either parental race. Hence it 

 may have a better chance of survival than an individual of either 

 parent stock. It is a difficult question, that we cannot answer at 

 present, whether a mixed strain has a better chance of survival 

 than one or another of the strains of which it is made up. The 

 possibility that some hybrid strains may be better than either pure 

 strain is enough to put one on his guard against the popular doc- 

 trine of racial purity so-called. Whatever advantages some kinds 

 of pure races of mankind may have, from a political, religious or 

 militaristic viewpoint, this should not blind us to the possibility of 

 the biological advantages that certain mixtures may bring about. 

 I emphasize the statement that certain mixtures of races may have 

 a biological advantage. It is equally possible that other combina- 

 tions may have a biological disadvantage. We are far from being 

 able to state at present what combinations are beneficial and what 

 are biologically injurious. It is an interesting problem, one of 

 deep significance I think for the future of the human race, but 

 mixed up as it is at present with difficult social and political ques- 

 tions it is a problem that only a light-hearted amateur or a politi- 

 cian is likely to be dogmatic about. 



Before we take up the main questions before us this evening, 

 I must speak of one other form of heredity. In many instances 

 we have evidence that a character is the product of more than -\ 

 single mutant gene. I say "mutant gene" because in fact every 

 character is no doubt the product of the combined action of many 

 genes, but in addition to this general relation there are many cases 

 now known where there are several specific genes whose chief 

 effect is on one character. Size differences furnish abundant 

 data of this sort. One of the clearest cases is that of the size of 

 the ear of corn. Some races of corn have short ears (and cobs ) , 

 some long. If two such races are crossed, the hybrid is inter- 

 mediate with a considerable range of variation. If the hybrid is 



