ASSORTATIVE MATINCI IN MAN. 



A COOPERATIVE STUDY. 



1. In considering the reproductioii Jind progressive change of a population 

 the pari played by any tonn of differential inating vvithiii the population niust be 

 given its due weight. Darwin has given the name of sexual selection to the 

 general conception of differential mating, biit it seems necessary now to distinguish 

 betweeii varions typcs of ditJerential inatiug. As opposed to pure randoni mating 

 within tlie p(.)pulation*, \ve have fiv^t jireferential inating, in which male or feinale 

 classes with certain values of a charaeter Hiid it less easy to iiiate thaii other 

 cksses with differeiit values. Seeondly \ve have assortative inatiiKj in which, while 

 all classes of niales and females find mates, certain classes of niales appear to be 

 attracted to certain classes of females. If the male class of a given character tends 

 to mate with a female class with generally like character, we have a tendency to 

 homofjmny. Homogamy as one type of assortative mating is simply measured by 

 the correlation betweeu the two characters in the male and female of the pair. 

 The influence of homogamy on the character of successive generations of a population 

 may be very great indeed, and the whole ränge of effect from pure random matings 

 to perfectly hoinogamous uuions within a population is almost but not (piite as 

 important as the ditference between seif and cross fertilisation in plants. It has 

 the distinctive featuros as compared with self-fertilisation, that (i) it may have any 

 degree of intensity, (ii) it may be confinod to special characters, and (iii) it is not 

 complicated by any of the supposed harmful eiilects of in-breeding. 



Theoretically the effect of assortative mating on ottspring — espeeially its 

 influence on the segregation of types — is very great, and it beconies of fundamental 

 importance to ascertain how far it exists in actual populations, which arc often 

 a priori assumed to mate at random. The preseut cooperative study forms an 

 attempt to measure the extent of assortative mating in man, by, not so niuch 

 a Single physical character, as the resulting etfect of a complex of physical 

 characters. It has been suggested that the duration of life is to .some extent 

 a rough measure of the general physical fitness to environment of an individual. 



• By random vuiting we understand theoretically a State of affairs in which every type of male would 

 be mated with every type of female, the random mating being with regard to one, two, three, many or 

 all characters. 



