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 matingin man. ‘‘ Whether the 
preference arises from greater sex instincts or from the esthetic 
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 marry. 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 
