Biomedical subjects

R Sear

Publications and source records attributed to R Sear.

At least 19 recordsLinked to original sources

PubMed2004

An evolutionary model of stature, age at first birth and reproductive success in Gambian women.

We have built a model to predict optimal age at first birth for women in a natural fertility population. The only existing fully evolutionary model, based on Ache hunter-gatherers, argues that as women gain weight, their fertility (rate of giving birth) increases-thus age at first birth represents a trade-off between time allocated to weight gain and greater fertility when mature. We identify the life-history implications of female age at first birth in a Gambian population, using uniquely detailed longitudinal data collected from 1950 to date. We use height rather than weight as an indicator of growth as it is more strongly correlated with age at first birth. Stature does not greatly influence fertility in this population but has a significant effect on offspring mortality. We model age at first reproduction as a trade-off between the time spent growing and reduced infant mortality after maturation. Parameters derived from this population are fitted to show that the predicted optimal mean age of first birth, which maximizes reproductive success, is 18 years, very close to that observed. The reaction norm associated with variation in growth rate during childhood also satisfactorily predicts the variation in age at first birth.

Adolescent↗

PubMed2000

Maternal grandmothers improve nutritional status and survival of children in rural Gambia.

Hypotheses for the evolution of human female life-history characteristics have often focused on the social nature of human societies, which allows women to share the burden of childcare and provisioning amongst other members of their kin group. We test the hypothesis that child health and survival probabilities will be improved by the presence of kin using a longitudinal database from rural Gambia. We find that the only kin to improve the nutritional status of children significantly (apart from mothers) are maternal grandmothers, and that this is reflected in higher survival probabilities for children with living maternal grandmothers. There is also evidence that the reproductive status of the maternal grandmother influences child nutrition, with young children being taller in the presence of non-reproductive grandmothers than grandmothers who are still reproductively active. Paternal grandmothers and male kin, including fathers, have negligible impacts on the nutritional status and survival of children.

Child, Preschool↗

PubMed1997

Birth interval and the sex of children in a traditional African population: an evolutionary analysis.

Birth interval is a major determinant of rates of fertility, and is also a measure of parental investment in a child. In this paper the length of the birth interval in a traditional African population is analysed by sex of children. Birth intervals after the birth of a boy were significantly longer than after the birth of a girl, indicating higher parental investment in boys. However, in women of high parity, this differential disappeared. Birth intervals for women with no son were shorter than for those with at least one son. All these results are compatible with an evolutionary analysis of reproductive decision-making. First born sons have particularly high reproductive success, daughters have average reproductive success and late born sons have low reproductive success. The birth interval follows a similar trend, suggesting that longer birth intervals represent higher maternal investment in children of high reproductive potential.

Adult↗

PubMed1996

Maternal mortality in a Kenyan pastoralist population.

OBJECTIVE: To measure maternal mortality among the Gabbra, a group of nomadic pastoralists living in a remote area of Kenya. METHOD: As part of a survey of 851 households, information on the number of sisters of respondents who died of pregnancy-related causes was collected and the data were used to calculate maternal mortality statistics using the sisterhood (an indirect) method. RESULTS: The maternal mortality ratio for this population was 599 deaths per 100,000 births (95% C.I. 424-775). The lifetime risk of dying around childbirth is 1 in 30, and the proportion of ever-married sisters that died under 50 years of age who died from maternal causes is 0.48 (95% C.I. 0.38-0.58). CONCLUSION: The risk of dying of maternal causes is high in this population.

Adolescent↗

PubMed1980

A summary of the results of radioisotope brain scans on a large series of patients.

The results are reported of 2830 radioisotope brain scans, the records for which have been reviewed one year after scanning over a period of ten years before CT scan facilities were available on site. Out of 766 lesions confirmed by other means 672 were detected by scanning. The majority of the space-occupying lesions that went undetected did so either because they were situated low down in the brain, e.g. small acoustic neuromas, pituitary fossa tumours and brain stem lesions, or they were astrocytomas or cystic lesions. Of 2064 cases with a negative clinical diagnosis all but 28 had negative brain scans. The high accuracy with which many types of space-occupying lesion can be excluded by this non-invasive, atraumatic technique confirms its continuing value where access to a CT scanner is limited.

Brain↗

PubMed1978