An investigation into assortative mating.

B Y assortative mating we mean the tendency of one sort of person to mate with another specific sort of person, and not entirely at random. One might think perhaps that the dark-skinned and dark-haired might be especially attracted to the blue-eyed and fair-haired, and vice versa. In fact, wherever the matter has been gone into, it is the opposite that holds, and it is always a matter of like attracting like and never unlike. This is true of such things as hair and eye colour and other anthropometric characters, and perhaps most importantly of intelligence. Husbands and wives have been found to resemble each other as closely in intelligence as brothers and sisters (Jones, I929). The importance of this from the evolutionary point of view cannot be overemphasized. A general tendency of like to mate with like, what is often called homogamy, if it extended over a wide range of hereditarily determined biological qualities, would amount very nearly to intensive inbreeding. It would have the same effect as inbreeding in increasing the variability of the population, and so increase its genetical instability and vulnerability to selective forces. If, as seems certain, the intelligent have At the present time fewer children than the unintelligent, then the marriage of two intelligent people to each other means that both of them are part sterilized; whereas if they both married unintelligent partners, whether the marriage were fecund or not, both intelligence and the lack of it would be equally penalized or favoured. Nearly all the work on assortative mating has been done in the U.S.A. by sociologists, and relates to modes of social behaviour, attitudes and interests. There is also a certain amount of work on physical characters, but extremely little in the realm of psychiatry. Professor Penrose (I944) has * A paper read before the Eugenics Society on January 15th, I946. shown that for one mental hospital in Canada the frequency of both husband and wife being admitted with a psychotic illness was much greater than chance probability would suggest, and he concludes that assortative mating does exist " with respect to traits which form part of the background of mental disease." On the other hand Leistenschneider (I938) found that the incidence of schizophrenia in the families of the consorts of schizophrenics was not significantly greater than in the general population. This finding, of limited interest though it is, is of great significance when the highly debated mode of inheritance of schizophrenia is considered. Everyone who has been concerned with the problem during the past war has been greatly impressed with the great frequency and importance of neurotic illnesses in the population. It is generally agreed that, however reactive these illnesses .may be to various forms of environmental stress, they have also a genetical basis Which can show itself in emotional instability and various. deviations of personality. I was therefore very glad to take an opportunity, which was made possible by the munificence of the Rockefeller Foundation, to institute an enquiry into the intensity of assortative mating as far as traits of personality were concerned. The investigation was planned in the following way. A psychiatric social worker, Mrs. Moya Woodside, our second speaker to-night,* interviewed a number of soldiers from the neurotic wards of my hospital. From each of them she obtained a social and psychiatric history, including family history, number and ages of sibs, early life and upbringing, school and occupational career, and the history of the marriage. A specially devised test of temperamental traits, which has been standardized on nonnal and neurotic soldiers, was also given. She also obtained from the