34 Cunningham, Unisexual Inheritance. 



siders the various forms of sexual selection. Of this he distinguishes 

 five forms, one of which termed apolegamic or preferential mating is 

 stated to be selection in the narrower sense of Darwin, while another 

 is assortative mating, the selection of like by like, preference not for 

 a mate in which certain characters are most developed, but for a mate 

 most similar to the seeker. He does not consider all the forms in 

 detail, but in his own words contents himself with some illustrations 

 of how exact quantitative methods can be applied to the problems of 

 apolegamic and homogamic mating". 



His application of quantitative methods consists in ascertaining 

 whether preferential mating is actually taking place with regard to 

 given characters. In the whole of the discussion not a word is said 

 as to the consequence of the selection, as to the interpretation or ex- 

 planation of the existence of constant differences between the sexes. 

 In fact, Professor Pearson seems to have in mind the question whether 

 it is possible to demonstrate by measurements and numbers that both 

 progressive change of type in a single race, and the differentiation of 

 one race into two or more, actually take place as the result >of 

 variation and selection. He remarks that without a barrier to inter- 

 crossing during differentiation the origin of species seems inexplicable". 

 He considers sexual selection as merely forming a barrier to inter- 

 crossing: to quote his words: ,,By sexual selection I would understand 

 something rather more than Darwin includes by that term, namely, 

 all differential mating due to taste, habit, or circumstance, which pre- 

 vents a form of life from freely intercrossing." But of sexual selection 

 in the true Darwinian sense, as a part of the theory of sexual dimor- 

 phism, and the explanation of the evolution of conspicuous characters 

 which are either useless or even harmful in ordinary life, Professor 

 Pearson seems to have no conception whatever. 



He takes the case of stature in the human race and ascertains 

 from actual measurements what differences there are in type and 

 variability between husbands, and men in general, or between wives 

 and women in general. He finds that in no case, except in the type 

 in the case of women, is there any certain difference, and in that 

 exception the difference is not ,,significant". The statistics, he says, 

 only run to a few hundreds, and were not specially collected for the 

 purpose; still so far as they go they show no evidence in mankind 

 of preferential mating with respect to stature, or of any character 

 very closely correlated with stature. And yet stature is one of the 

 characters in which human beings are most distinctly dimorphic 

 sexually. If we take from Professor Pearson's figures the difference 

 in type between husbands and wives instead of between husbands and 

 men in general, it is 5.267 inches, while the difference in variability is 

 very slight. Professor Pearson makes no remark on this. 



