A review of the pattern and magnitude of nero–white mating in the US is presented from the time of the earliest arrival of negroes in the American colonies until the present, using historical, demographic, census and genetic evidence.

The relative magnitude of negro male–white female matings compared to the converse are analysed in view of the different genetic outcomes of these two types of mating for X-linked genes. Contrary to many strongly stated opinions it is conclued from the historical evidence that, even from the earliest days of slavery, negro male–white female matings were a significant proportion of all negro–white matings. Census and demographic evidence suggests that their frequency increased so that from the time of the Civil War on they have formed a majority of inter-racial matings.

Genetic evidence based on estimates of the amout of admixture of white genes in a number of negro populations is considered. Estimates of admixture for the X-linked genes G6PD, and those for colour blindness are as high or higher than those derived from comparable autosomal genes.

Some observations on the total magnitude of negro–white mating, on the phenomenon of passing and on the relative socio-economic status of those involved are also made.

The implication of the findings on these phenomena for investigations and hypotheses concerning differences in intelligence and intellectual abilites between the races, particulary spatial ability which is thought to be strongly influenced by a gene on the X chromosome, are considered.

It is concluded that some of the assumptions made in proposing hypotheses regarding the origin and distribution of these abilities in the American negro are at variance with genetic, historical and sociological findings.

An intensive pilot survey involving direct contact with 47 young married couples with university education was conducted to determone their attitudes tiwards general (public) and personal choice and control by parents of the sex of offspring. Information as to premarital family status and present number and sex of children was obained. Questionnaires were completed before and after information had provided regarding new methods of fetal sex detemination, abortion, and related topics. Opportunity for discussion by husband and wife between sessions was allowed, but discussion with other was discouraged. Results indicate that sex choice will be accepted and employed by the majority of highly educated, middle-class individuals. While selection of the first-child sex is of negligible importance to most, planning for a second child with opposite sex to the first is strongly favoured. The tendency to prefer males is not as pronounced as reported in previous, less direct studies. The majority preferred a two-child family with one child of each sex. Prospective methods (e.g. a pre-coital, sex-selective pill, when available) were much preferred to retrospective methods involving abortion. Inthe meantime, fetal sex determination in the first trimester of pregnancy with selective abortion may soon be widely practised. New problems in marital and family adjustment, family planning, and social organization may arise with the advent of this new step in human sexual socio-econtingencies need further onvestigation at various socia-economic and educational levels and in different cultural milieus.

Data are employed from six surveys carried out in Ibadan City, Nigeria, during two survey programmes: the Nigerian segment of the Changing African Family Project in 1973, and the Nigerian Family Study in 1974–5. A distinction is made between contraceptive innovators, those who use any means to control fertility except the traditional Yoruba sexual abstinence, and demographic innovators, those who succeed in limiting their family size. It is shown that contraceptive innovation is now proceeding rapidly but has little connection with demographic innovation. Contraceptive innovation is a response to social change which has increased the likelihood of premarital and extramarital sexual relations and the desire to shorten the period of postnatal sexual abstinence while not increasing the interval between births. Such innovation has proceeded more rapidly because of the increased availability of contraceptives since about 1960 and because of the types of contraceptives which have been developed since then. Demographic innovation is on the increase but its incidence is still minute. Fertility restriction within marriages seems to take place only after profound changes have occurred in the economic relationships within both the extended and nuclear families which for the first time make the small family the economically rational choice. Such change probably depends more on the import of cultural patterns than on necessary cultural adjustments to imported economic change, but a strengthening of the conjugal bond is involved and this may be hastened by contraceptive innovation. Little innovational trauma or even awareness of profound change was detected, largely because the profound, and even disruptive, innovations are preceding social ones, but partly too because peer group behaviour changes at much the same time.

In 1968, a prospective study was started in collaboration with the Family Planning Association to try to provide a balanced view of the beneficial and harmful effects of different methods of contraception. This investigation is now in progress at seventeen clinics and over 17,000 women are under observation. At the time of recruitment, all these women were married white British subjects, aged 25–39 years, who voluntarily agreed to participate. Fifty-six per cent were using oral contraceptives, 25% were using a diaphragm and 19% were using an intrauterine device (IUD). During follow-up each woman is questioned at return visits to the clinic and a record of pregnancies and their outcome, hospital referrals (inpatient or outpatient), changes in contraceptive methods and the results of cervical smears, is accumulated. Women who default are sent a postal questionnaire and, if this is not returned, are telephoned or visited in their homes to collect the necessary information.

So far, data obtained during 56,000 woman-years of observation are available for analysis. Follow-up has been maintained with an annual lapse rate of about 0.3%due to withdrawal of co-operation or loss of contact; adherence to the method of contraception in use at recruitment has been reasonably good, and the reporting of pregnancies and hospital admissions appears to have been both reliable and unbiased.

The present data include only 24 deaths, so the mortality associated with different contraceptive methods cannot yet be estimated. With regard to morbidity, however, our preliminary results closely resemble those obtained in the prospective study carried out by the Royal College of General Practitioners (1974) and in the principal retrospective studies carried out in Britain and the United States. Women who used oral contraceptives at the start of the study experienced a deficiency of hospital referrals for cancer, benign lesions of the breast, menstrual disorders other than amenorrhoea, duodenal ulcer, and retention cysts of the ovary; they showed an excess of referrals for cerebrovascular disease, cervical erosion, skin disorders, self-poisoning, migraine, venous thrombosis and embolism, hayfever, gallbladder disease, amenorrhoea, and sterility. Women who used a diaphragm showed a deficiency of hospital referrals for carcinoma-in-situ and dysplastic lesions of the cervix uteri and accidental injury; and an excess of referrals for haemorrhoids and cystitis. Women who used an IUD experienced an excess of hospital referrals for anaemia, varicose veins and salpingitis. About half of these differences (12 out of 23) were predicted from other studies while some suggestive evidence already existed for a further five. Of the remaining six, some probably reflect the influence of selective factors or chance.

Multiple pregnancies, stillbirths, malformations, the sex ratio and birthweight showed no consistent relationship to method of contraception. The outcome of unplanned pregnancies occurring in women using an IUD, however, was remarkably unfavourable both in terms of ectopic gestation and miscarriage.

Clear evidence was found of impairment of fertility after discontinuation of oral contraceptives. Whether this is likely to lead to permanent sterility in some women is uncertain.

The study has provided data on the efficacy of a wide variety of contraceptive methods. In general the failure rates are in keeping with those obtained in other large-scale studies, save that those for the diaphragm and the sheath are much lower than those usually quoted.

The available evidence does not yet allow a final balance to be struck between the benefits and risks associated with the new methods of contraception that have become widely used during the last two decades. It seems clear, however, that there are no material risks associated with the use of the diaphragm apart from the risk of pregnancy and that there may be some unintended benefits.