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Ruth Mace

Publications and source records attributed to Ruth Mace.

10 recordsLinked to original sources
PubMed2006

Polygyny, reproductive success and child health in rural Ethiopia: why marry a married man?

This study examines the reproductive success of men and women in rural Ethiopia as a function of their marital status, specifically by comparing polygamously and monogamously married individuals. In line with predictions from evolutionary theory, polygamy is beneficial to male reproductive success (i.e. producing larger numbers of surviving offspring). The success of polygamously married females depends on wife rank: the first wives of polygamous husbands do better than monogamously married women and much better than second or third wives. These effects are mirrored in child nutritional status: the children of second and third wives have lower weight for height. Due to potential, largely unmeasurable differences in marriageability (quality) between individuals, it was not possible to support a model of either resource-holding polygyny combined with female choice or female coercion into unwanted marriages. First wives of polygamously married men marry at a younger age and attract a higher brideprice, suggesting that both the males and females in the marriage are likely to be of higher quality (due to wealth, family status or some other factor such as beauty). Unions that end up monogamous are likely to be between slightly lower quality individuals; and second and third wives, who marry at the oldest ages and attract the lowest brideprice, may be 'making the best of a bad job'. The relatively long gap between first and second marriages may mean that first wives of highly marriageable males can enjoy considerable reproductive success before their husbands marry again.

Adolescent↗
PubMed2006

An energy-saving development initiative increases birth rate and childhood malnutrition in rural Ethiopia.

BACKGROUND: Evolutionary life history theory predicts that, in the absence of contraception, any enhancement of maternal condition can increase human fertility. Energetic trade-offs are likely to be resolved in favour of maximizing reproductive success rather than health or longevity. Here we find support for the hypothesis that development initiatives designed to improve maternal and child welfare may also incur costs associated with increased family sizes if they do not include a family planning component. METHODS AND FINDINGS: Demographic and anthropometric data were collected in a rural Ethiopian community benefiting from a recent labour-saving development technology that reduces women's energetic expenditure (n = 1,976 households). Using logistic hazards models and general linear modelling techniques, we found that whilst infant mortality has declined, the birth rate has increased, causing greater scarcity of resources within households. CONCLUSIONS: This study is, to our knowledge, the first to demonstrate a link between a technological development intervention and an increase in both birth rate and childhood malnutrition. Women's nutritional status was not improved by the energy-saving technology, because energy was diverted into higher birth rates. We argue that the contribution of biological processes to increased birth rates in areas of the developing world without access to modern contraception has been overlooked. This highlights the continued need for development programmes to be multisectoral, including access to and promotion of contraception.

Adolescent↗
PubMed2004

A phylogenetic approach to cultural evolution.

There has been a rapid increase in the use of phylogenetic methods to study the evolution of languages and culture. Languages fit a tree model of evolution well, at least in their basic vocabulary, challenging the view that blending, or admixture among neighbouring groups, was predominant in cultural history. Here, we argue that we can use language trees to test hypotheses about not only cultural history and diversification, but also bio-cultural adaptation. Phylogenetic comparative methods take account of the non-independence of cultures (Galton's problem), which can cause spurious statistical associations in comparative analyses. Advances in phylogenetic methods offer new possibilities for the analysis of cultural evolution, including estimating the rate of evolution and the direction of coevolutionary change of traits on the tree. They also enable phylogenetic uncertainty to be incorporated into the analyses, so that one does not have to treat phylogenetic trees as if they were known without error.

Journal Article↗
PubMed2003

Spread of cattle led to the loss of matrilineal descent in Africa: a coevolutionary analysis.

Matrilineal descent is rare in human societies that keep large livestock. However, this negative correlation does not provide reliable evidence that livestock and descent rules are functionally related, because human cultures are not statistically independent owing to their historical relationships (Galton's problem). We tested the hypothesis that when matrilineal cultures acquire cattle they become patrilineal using a sample of 68 Bantu- and Bantoid-speaking populations from sub-Saharan Africa. We used a phylogenetic comparative method to control for Galton's problem, and a maximum-parsimony Bantu language tree as a model of population history. We tested for coevolution between cattle and descent. We also tested the direction of cultural evolution--were cattle acquired before matriliny was lost? The results support the hypothesis that acquiring cattle led formerly matrilineal Bantu-speaking cultures to change to patrilineal or mixed descent. We discuss possible reasons for matriliny's association with horticulture and its rarity in pastoralist societies. We outline the daughter-biased parental investment hypothesis for matriliny, which is supported by data on sex, wealth and reproductive success from two African societies, the matrilineal Chewa in Malawi and the patrilineal Gabbra in Kenya.

Africa South of the Sahara↗
PubMed2003

Strong mothers bear more sons in rural Ethiopia.

In humans, there is evidence that the physiological cost to the mother of bearing sons is greater than of bearing daughters. Parents should manipulate the sex of offspring born in response to resource availability to maximize their reproductive success. Here, we demonstrate that, within a rural food-stressed community in southern Ethiopia, there is a strong association between the sex of the most recent birth and maternal nutritional status, measured either by body mass index or mid-upper arm muscle area (AMA) (measures of fat and muscle mass). The effect of muscle mass is very marked: those women in the upper 25th percentile of AMA were more than twice as likely to have had a recent male birth than those in the lowest 25th percentile.

Ethiopia↗
PubMed2003

Testing evolutionary hypotheses about human biological adaptation using cross-cultural comparison.

Physiological data from a range of human populations living in different environments can provide valuable information for testing evolutionary hypotheses about human adaptation. By taking into account the effects of population history, phylogenetic comparative methods can help us determine whether variation results from selection due to particular environmental variables. These selective forces could even be due to cultural traits-which means that gene-culture co-evolution may be occurring. In this paper, we outline two examples of the use of these approaches to test adaptive hypotheses that explain global variation in two physiological traits: the first is lactose digestion capacity in adults, and the second is population sex-ratio at birth. We show that lower than average sex ratio at birth is associated with high fertility, and argue that global variation in sex ratio at birth has evolved as a response to the high physiological costs of producing boys in high fertility populations.

Adaptation, Physiological↗
PubMed2002

The effects of kin on child mortality in rural Gambia.

We analyzed data that were collected continuously between 1950 and 1974 from a rural area of the Gambia to determine the effects of kin on child mortality. Multilevel event-history models were used to demonstrate that having a living mother, maternal grandmother, or elder sisters had a significant positive effect on the survival probabilities of children, whereas having a living father, paternal grandmother, grandfather, or elder brothers had no effect. The mother's remarriage to a new husband had a detrimental effect on child survival, but there was little difference in the mortality rates of children who were born to monogamous or polygynous fathers. The implications of these results for understanding the evolution of human life-history are discussed.

Demography↗
PubMed2002

The impact of labor-saving technology on first birth intervals in rural Ethiopia.

Across the developing world labor-saving technologies introduce considerable savings in the time and energy that women allocate to work. Hormonal studies on natural fertility populations indicate that such a reduction in energetic expenditure (rather than improved nutritional status alone) can lead to increased ovarian function. Other qualitative studies have highlighted a link between labor-saving technology and behavioral changes affecting subsequent age at marriage, which may affect fertility. This biodemographic study was designed to investigate whether these physiological and behavioral changes affect fertility at a population level by focusing on a recent water development scheme in Southern Ethiopia. The demographic consequences of a reduction in women's workload following the installation of water points, specifically the variation in length of first birth interval (time lapsed between marriage and first birth), are investigated. First birth interval length is closely associated with lifetime fertility in populations that do not practice contraception, longer intervals being associated with lower fertility. Using life tables and multivariate hazard modeling techniques a number of significant predictors of first birth interval length are identified. Covariates such as age at marriage, season of marriage, village ecology, and access to improved water supply have significant effects on variation in first birth intervals. When entered into models as a time-varying covariate, access to a water tap stand is associated with an immediate reduction in length of first birth intervals.

Adolescent↗