It has been suggested that average genetic similarity, as assessed by blood genetic markers, could influence mate choice in humans. In the present study, average genetic similarity was assessed in 183 couples submitting to paternity determinations in relation to six blood group systems and three HLA loci. Couples in which the putative father was excluded were compared with those in which such exclusion did not occur, and real couples were compared to random pairs. The differences were all statistically non-significant. Possible reasons for the different results found in the previous sample and in the present study are considered.

The accuracy of responses to a question on the frequency of sexual intercourse in the 4-week period prior to an interview is expected to be low. This paper examines the reliability of an alternative question: ‘How many days since you last had sexual intercourse?’. This was a part of a larger longitudinal study of fertility dynamics in Matlab, Bangladesh. The response pairs of 61 women who were asked the same question by an interviewer and on the next day by a supervisor, were analysed. Refusals were more common among older women and among women who gave a response at the extremes of the distribution for the other interview. Of the pairs of two responses, 78% had a difference of 3 days or less. Further study and use of the question on days since last intercourse is recommended.

Relationships were examined between sibling variables, perceptions of learning environments and aspirations for Australian adolescents from family contexts defined conjointly by human and social capital. Generally, the findings using a regression approach indicated that sibling variables continued to have significant and often complex associations with adolescents' aspirations after taking into account relationships between perceptions of learning environments and aspirations. Also, relationships between sibling variables, perceptions of learning environments and aspirations, varied for adolescents from the different family contexts.

Postpartum sexual abstinence may be a major determinant of fertility and of maternal and child health in sub-Saharan Africa. This study examines the relationship between ethnicity and abstinence using data from the 1988 Ghana Demographic and Health Survey. There is considerable diversity in the length of abstinence although only for one ethnic group, the Mole-Dagbani and other Ghanaians, is abstinence, both actual and ideal, very long. Respondents in most ethnic groups believe their abstinence to be adequate. A key motivation for abstinence is the unwillingness to have sexual intercourse with nursing mothers. Education, urbanisation, changes in marriage patterns and religious traditions are major factors shaping the ethnic differentials in abstinence. In comparison to breast-feeding, abstinence appears to have relatively little impact on the length of the birth interval and, for Ghana, has relatively few implications for fertility and child health.

The degree of isolation was assessed in two contrasting regions in Northern Palencia, Spain, one mountainous with small villages in the valleys (Pernia), the other lower and more open (Ojeda), with corresponding differences in economy. Using data from the parish and diocesan records, the frequencies of consanguineous marriages were calculated from the dispensation data, and the evolution of inbreeding compared. The more isolated region shows a greater degree of inbreeding, though not as high as in some other parts of Spain. Both regions show a decline in inbreeding with time, though in neither did the results indicate that geographic isolation was very outstanding. The most frequent types of consanguineous unions occur between second cousins.

This study examines the extent of assortative mating for education in Northern Sudan and urban Khartoum. More males than females were found at higher levels of education. Increasingly, people tend to marry persons of equal educational level, but the unequal educational opportunities for males and females have led to the emergence of educational exogamy in which members of different educational levels are more likely to marry from the adjacent educational category than from distant categories. The increasing level of education for both sexes, and especially for females, may in part explain the rising trend in age at marriage.

Onset of capacity for childbearing in women is dated biologically by menarche, although actual onset may be delayed. The end of childbearing is less understood but recent demographic and biological research on fertility at older ages is clarifying the end of fertility.

The demographic view of declining fertility with age is based on age-specific fertility in natural fertility populations, artificial insemination and pregnancy rates by age and World Fertility Survey data. New data from the Demographic and Health Surveys on exposure to the risk of pregnancy shows that whereas older women biologically need longer exposure to pregnancy, exposure declines on behavioural grounds such as duration of marriage. Actual fecundity is obscured by factors of fecundability. Recent research on medically assisted conception is adding to the understanding of declining fecundity with age, especially the relative contributions of endometrial and ovarian ageing.

This paper reviews the available information on declining fertility with age and discusses the implications of the extension of fertility through new medical technologies.

Factors affecting desired family size in rural Bangladesh are examined using data from contraceptive prevalence surveys conducted between 1983 and 1991. The analysis suggests that mothers having two sons and one daughter are more inclined to perceive their family as complete than those having three sons and no daughter. Logistic regression analysis indicates that important determinants of desire for more children are age of woman, current contraceptive use status, work status, and family planning worker's visit. The policy implications of these findings are discussed.

The traditional preference for sons may be the main hindrance to India's current population policy of two children per family. In this study, the effects of various sociodemographic covariates, particularly sex preference, on the length of the third birth interval are examined for the scheduled caste population in Assam, India. Life table and hazards regression techniques are applied to retrospective sample data. The analysis shows that couples having two surviving sons are less likely to have a third child than those without a surviving son and those with only one surviving son. Age at first marriage, length of preceding birth intervals, age of mother, and household income have strong effects on the length of the third birth interval.

The evidence from gynaecologists in Northern Ireland shows confusion in interpretation and practice of abortion law, with some women even being denied abortion after rape. Over two-thirds of gynaecologists supported a change in the law which would leave the abortion decision to the woman and her doctor, but less than half wanted the introduction of the British law.

This article examines the mechanisms of subsistence adaptation of two Papua New Guinea populations, the Metroxylon sago-depending lowland Gidra and the taro-monoculture Mountain Ok, surviving in low population densities of 0·5 and 1·4 persons per km2. Observation of the groups' land use systems strongly suggests that their population densities have not been far below the carrying capacity, although the territory of each population is markedly heterogeneous. Both groups have maintained their sustainable food production not only for resource management but also for survival at a population level, either expanding their territory or changing the sustainable level in tandem with changes of subsistence system.

This report examines the consequences of a positive HIV diagnosis upon the reproductive decision-making of 39 men and women in Scotland. Whilst the majority initially decide never to have any (more) children this sometimes changes as other factors gain ascendancy, such as a partner wanting ‘their’ child, and about one-third had had a child or were intending to do so. The motivations underlying such decisions are discussed and ways in which health services could intervene to support people with HIV in making reproductive choices and to minimise the risk of transmission to an HIV-negative partner and the child are suggested.