Data were collected from 368 Rwanda women, 50 non-lactating and 318 lactating, to determine the effect of lactation on conception rate and the return of menstruation. During lactation the majority of conceptions were found to be delayed by some 15 months, but the family spacing effect was maximal during the first 9 months. By 27 months after delivery the contraceptive effect of lactation can be assumed to have largely disappeared.

The birth rates per 1000 married females of specified ages and durations of marriage generally attained their post-war maxima in 1946–47 and then declined. While this declining trend was a brief one for females of younger ages and shorter durations of marriage, it continued for females of older ages and longer durations. Since 1961 the rates for all (younger and older) women have declined markedly. Does this recent decline in annual fertility, especially that for females of younger ages and shorter durations of marriage, herald a decline in the total fertility of cohorts who have not yet completed their childbearing? Many believe it to be so. However, an examination of the cumulative fertility of cohorts marrying since 1936 showed that (a) the total fertility of cohorts who have completed their childbearing varied between a narrow range of 2500–3000 and (b) the cumulative fertility up to 5 or 10 years of marriage duration of later cohorts was considerably higher (13–40% higher) than that of earlier cohorts. These facts, and similar ones for Australia covering a wider period (Basavarajappa, 1964), are thought to suggest that the total fertility of cohorts who have not yet completed their childbearing might not be far outside the limits of 2500 and 3000.

There are as yet few studies of body hair variation in man. Of all human populations, the Ainu of Japan are most famous for their alleged hirsuteness, and the history of this somewhat controversial subject is reviewed. Data are presented on chest, back and facial hair pattern and quantity in a sample of Ainu and Ainu/Japanese hybrids, resulting initially from field work by the Cambridge Expedition to Northern Japan in 1964. Methodological problems are discussed. Social attitudes to hairiness in Japan over the past few centuries are commented on, in view of their possible relevance in maintaining the biological distinctiveness of the Ainu. It is concluded that although the Ainu have more body hair than other Japanese, compared with some other groups—for instance American ‘Whites’—they can not be considered exceptionally hirsute.

Using Australian records of human births for the first six decades of the twentieth century, the proportions of male and female births are studied in relation to the mother's age, the father's age, the parents' ages in combination, and certain other factors. The principal data used relate to the years 1931–55, during which over 3 million children were born, yet even so the significant features are not easy to discern.

Masculinity tends to fall as the age of either parent increases. But it is only average or below if one parent is old while the other is young. For high masculinity, both parents must be young.

The Australian data are available in a form which enables the sex ratio to be studied also in relation to (a) the season of the year; (b) urban and rural areas; (c) the different states of the Commonwealth; (d) births inside and outside marriage; and (e) single and multiple births. When the influence of the parents' ages is eliminated, however, it does not appear as though the sex ratio varies significantly with any of these factors.

Reproductive performance and some of the more important features of their progeny were studied in 755 radiologists and in 346 laboratorians as controls in order to investigate the possible genetic injuriousness of ionizing radiation. Significant differences were found only in fertility: the fertility of female radiologists was significantly lower than that of the female laboratorians and of the wives of male radiologists. This phenomenon is probably explained by a more extended use of the methods of birth control by female radiologists due to roentgenophobia.

A longitudinal study of the growth of a cohort of 229 infants born in a rural area in Jamaica and followed to their 4th birthdays is described, and this paper reports analyses of the anthropometric measurements.

Moderate impairment of growth affected the majority of children and was most marked between the ages of 3 and 15 months. Severe impairment occurred in boys more often than girls and in this comm unity was rarely attributable to disease.

The concept of weight faltering has been investigated in some detail; failure to gain weight for a period of 6 months occurred in almost half the children but was not, by itself, a useful prognostic index of malnutrition; it occurred commonly in children of above average weight whose subsequent growth was normal.

The provision of intensive care at specially appointed child welfare clinics did not completely prevent the development of serious malnutrition.

313 pairs of brothers and 296 pairs of sisters were compared by one or both parents in a postal questionnaire. For 495 pairs independent questionnaires were completed by father and mother, and agreement between parents was good.

There was a marked tendency for the first-born child to be rated as less fond of cuddling; he was also easier to train, worked harder at school, set himself higher standards, and was more serious, methodical, law-abiding, tidy and less impulsive; he learned to talk and read at a younger age and was rated as having more natural ability at schoolwork. These three groups of first-born attributes were relatively independent; for instance, even the first-born with less ability at schoolwork were given more responsibility at school. In the 152 pairs which did not contain a first-born, little birth order effect could be found, whether or not the elder was the eldest of his or her sex.

There was a slight tendency for the broader, fatter and more muscular child to be less nervous and highly strung, but otherwise differences in physique were not related to differences in behaviour. Abilities at schoolwork, games, music and painting were not related. Tendency to anxiety and depression was related to lack of sociability; to stubbornness and lack of practicality; to angryness but not the bottling up of anger; to level of aspiration but not the possession of abilities or good looks. These relations of anxiety and depression in a normal sample closely parallel the items which distinguish psychiatric patients from their healthy siblings.