SEXUAL SELECTION, ASSORTATIVE MATING, ETC. 229 



the race is the same as if they were chosen with relative 

 infrequency. 



Sexual selection in the strict Darwinian sense has been distin- 

 guished by Pearson from another form of selection which is 

 termed assortative mating. The former he designates as prefer- 

 ential mating. "If we wish to discuss," he says, "whether 

 preferential mating with regard to any organ or character is 

 taking place in a given form of life, we must investigate whether 

 the type and variability of the mated and unmated members of 

 one or the other sex are the same. If they are not, then sexual 

 selection in the form of preferential mating is undoubtedly at 

 work." Pearson has shown us from data collected by Francis 

 Galton that light-eyed people marry more frequently than dark- 

 eyed. There is thus a preferential mating in man. "Whether the 

 preference arises from greater sex instincts or from the aesthetic 

 sense is immaterial from the standpoint of evolution, however 

 interesting from the moral or social standpoint." 



Assortative mating is the union of like with like. It may occur 

 where the mated and the unmated do not differ in the average 

 development of any characteristic, or where all the individuals 

 become mated. The few studies of assortative mating in man 

 have shown, contrary to popular impression, that there is a 

 tendency of persons of like characteristics to msLvry. Fol by a 

 study of 251 photographs of young and old married couples 

 concluded that in the majority of cases (66.7 per cent in the 

 young and 71.7 per cent in the old) the parties were similar 

 instead of dissimilar. Galton's early studies {Natural Inheritance) 

 failed to show that people were much influenced in marriage by 

 similarities in stature, temper and artistic tastes. The mating of 

 couples with similar eye color was somewhat more frequent than 

 would be produced through mere chance unions. In his later 

 studies of the parents of English men of science Galton showed 

 that in temperament and color of eyes and hair the parents 

 showed a notable similarity. From more extensive data Pearson 

 has shown that light-eyed men tend to marry light-eyed women 

 more than dark-eyed, and that dark-eyed men tend to marry 



