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.     

Helpful grandmothers in rural Ethiopia: A study of the effect of kin on child survival and growth

Kin selection and parental investment theories state that, in highly social species, such as humans, individuals can increase their inclusive fitness by extending support to their relatives. Here, we document patterns of kin support in a rural Ethiopian community, where postmarital residence practices provide differential access to relatives. Using demographic, anthropometric, and behavioral data collected from four villages we are able to (a) identify the effects of the presence of kin on child mortality and growth patterns and (b) provide detailed information on the role of relatives within the household.

Mortality analyses indicate that grandmothers had a positive effect on child survival. Anthropometric data reveal that maternal grandmothers had a particularly beneficial effect on child height, but paternal grandmothers less so. Time allocation data suggest that grandmothers continued to visit their daughters' households, irrespective of postmarital residence, where they relieved their daughters of heavy domestic tasks rather than helping with direct grandchild care. Matrilocal postmarital residence was associated with improved child survival, although children in matrilocal households were actually smaller. This may be due to wealth effects, increased competition between siblings, or higher survival of smaller infants in matrilocal households.     

Hamilton's rule and kin competition: the Kipsigis case

Evolutionary studies of human behavior have emphasized the importance of kin selection in explaining social institutions and fitness outcomes. Our relatives can nevertheless be competitors as well as sources of altruism. This is particularly likely when there is local competition over resources, where conflict can lead to strife among nondispersing relatives, reducing or even negating the effects of relatedness on promoting altruism. Here, I present demographic data on a land-limited human population, utilizing large within-population variation in land ownership to determine the interactions between local resource competition and the benefits of kin in enhancing child survival, a key component of fitness in this population. As predicted, wealth affects the extent of kin altruism, in that paternal relatives (specifically father's brothers) appear to buffer young children from mortality much more effectively in rich than in poor households. This interaction effect is interpreted as evidence that the extent of nepotism among humans depends critically on resource availability. Further unanticipated evidence that maternal kin play a role in buffering children from mortality in situations where paternal kin control few resources speaks to the important role that specific local circumstance plays in shaping kin contributions to child welfare.     

Grandma plays favourites: X-chromosome relatedness and sex-specific childhood mortality

Biologists use genetic relatedness between family members to explain the evolution of many behavioural and developmental traits in humans, including altruism, kin investment and longevity. Women''s post-menopausal longevity in particular is linked to genetic relatedness between family members. According to the ‘grandmother hypothesis’, post-menopausal women can increase their genetic contribution to future generations by increasing the survivorship of their grandchildren. While some demographic studies have found evidence for this, others have found little support for it. Here, we re-model the predictions of the grandmother hypothesis by examining the genetic relatedness between grandmothers and grandchildren. We use this new model to re-evaluate the grandmother effect in seven previously studied human populations. Boys and girls differ in the per cent of genes they share with maternal versus paternal grandmothers because of differences in X-chromosome inheritance. Here, we demonstrate a relationship between X-chromosome inheritance and grandchild mortality in the presence of a grandmother. With this sex-specific and X-chromosome approach to interpreting mortality rates, we provide a new perspective on the prevailing theory for the evolution of human female longevity. This approach yields more consistent support for the grandmother hypothesis, and has implications for the study of human evolution.     

The effects of kin propinquity on infant mortality

This study tests the grandmother hypothesis and analyzes the effect of kin propinquity on infant mortality in a 19th century American frontier communal, polygynous population. The study shows that the presence of maternal grandmothers, aunts, uncles, and paternal aunts were significantly associated with increased infant survivorship while grandfathers, paternal grandmothers, and paternal uncles showed little effect. This study has implications for understanding the evolution of a long postreproductive life span, postmarital residential strategies, and behavioral strategies that enhance inclusive fitness.     

Kin influences on fertility in Thailand: Effects and mechanisms

It has been suggested that human mothers are cooperative breeders, as they need help from others to successfully raise offspring. Studies working under this framework have found correlations between the presence of kin and both child survival and female fertility rates. This study seeks to understand the proximate mechanisms by which kin influence fertility using data from the 1987 Thailand Demographic and Health Survey (DHS), a nationally representative sample of 6775 women. Kin influence is measured by the length of time couples live with the husband's or wife's parents after marriage. Event history analysis, multilevel modeling and structural equation modeling are used to investigate both fertility outcomes and potential pathways through which postnuptial residence may influence fertility outcomes, including employment status, maternal and child outcomes, contraceptive use, breastfeeding duration, and age at marriage. We show that living virilocally (with husband's kin after marriage) increases total fertility by shortening time from marriage to first birth, and increasing the likelihood of progression to each subsequent birth. These effects are mediated through correlations between virilocal residence and earlier age at marriage as well as delayed initiation of contraceptive use. We find no influence of husband's kin on maternal or child outcomes. Living uxorilocally (with wife's kin after marriage) also reduces age at marriage, shortens time from marriage to first birth and (marginally) improves child survivorship, but has no effect on other child and maternal outcomes or progression to subsequent births and results in a similar number of living children as women living neolocally.     

Kin and birth order effects on male child mortality: three East Asian populations, 1716–1945

Human child survival depends on adult investment, typically from parents. However, in spite of recent research advances on kin influence and birth order effects on human infant and child mortality, studies that directly examine the interaction of kin context and birth order on sibling differences in child mortality are still rare. Our study supplements this literature with new findings from large-scale individual-level panel data for three East Asian historical populations from northeast China (1789–1909), northeast Japan (1716–1870), and north Taiwan (1906–1945), where preference for sons and first-borns is common. We examine and compare male child mortality risks by presence/absence of co-resident parents, grandparents, and other kin, as well as their interaction effects with birth order. We apply discrete-time event-history analysis on over 172,000 observations of 69,125 boys aged 1–9 years old. We find that in all three populations, while the presence of parents is important for child survival, it is more beneficial to first/early-borns than to later-borns. Effects of other co-resident kin are however null or inconsistent between populations. Our findings underscore the importance of birth order in understanding how differential parental investment may produce child survival differentials between siblings.     

Infant and child mortality in Pakistan--some trends and differentials

Data from reproductive histories collected in the Population, Labor Force and Migration Survey (PLM) of 1979 are used to analyze trends and differentials in infant and child mortality in Pakistan. Comparisons with the Pakistan Fertility Survey (PFS) findings are also presented. The main concern is to provide from the latest national data, the PLM, direct measures of infant and child mortality and to demonstrate the relatively static and low chances of survival for children in Pakistan. The apparent trends from the PLM and the PFS are similar and seem to confirm that infant and childhood mortality has ceased to decline, at least rapidly, since 1965-69. Neonatal mortality is higher at levels of 70-85 deaths/1000 compared to postneonatal mortality of 40-60 deaths/1000. Improvements in neonatal rates from 1950 until 1975 are only approximately 1/2 of those for postneonatal rates for that period. The relationship between maternal age and mortality in the PLM data confirms that children of youngest mothers experienced the highest rates of infant mortality; mortality is again higher for children of oldest mothers aged 35 and above. The pattern of mortality in the 2 surveys is similar except that in the PFS there was little variation among births higher than 5th order. Sex differentials in mortality are very clear in both surveys. Boys have higher chances of dying in the 1st month of life but then the probability of their surviving from age 1 to 5 years is higher, reflecting the behavioral preference for the male sex in this society. The data also demonstrate an almost monotonic decline in infant and child mortality associated with longer birth intervals. Childhood mortality shows a less clear association with preceding birth interval than does infant mortality. While neonatal mortality is much higher in rural than in urban areas, there are negligible differences in the postneonatal rate. The urban-rural differential continues into childhood, reflecting lower health care and nutrition of children in rural areas. The data confirm the importance of parental education, particularly that of mothers, as a contributor to the health and mortality of infants. Mortality between age 1 and 5 years for children of the rural educated group is lower than that for the urban uneducated indicating the strong influence that education of mothers can have in preventing child loss. The combined evidence from the PFS and PLM data stresses the importance of improving health facilities in the rural areas, in aneffort to reduce the differences in mortality by area of residence. The data from both surveys also suggest the need to restrict motherhood to between the ages of 20 and 34, when obstetrical and health risks are minimal, and indicate the definite advantages of increasing the spacing between children.     

Vervet monkey grandmothers: Interactions with infant grandoffspring

Social relationships of 30 infants with their maternal grandmothers were studied in a captive colony of vervet monkeys (Cercopithecus aethiops sabaeus).Grandmothers and grandinfants formed affiliative relationships with one another that could be distinguished from the infant’s relationships with nonkin adult females and with other adult female kin. The intensity of the grandmother—grandinfant relationship varied according to several factors which were related to the infant’s vulnerability to mortality and to the grandmother’s ability to provide effective social support. High-ranking grandmothers spent more time near their grandinfants, and initiated more grooming and caretaking of their grandinfants, than did lower-ranking grandmothers. Grandmothers spent more time near their daughter’s first surviving infant than near later-born infants, and when grandmothers had more than one adult daughter, they spent more time near the infant of the younger daughter. These results, combined with the fact that the presence of a maternal grandmother has been associated with a reduction in the rate of infant mortality in this colony (Fairbanks and McGuire, 1986), suggest that grandmothers are actively contributing to the reproductive success of their adult daughters and to the survival of their infant grandoffspring.     

Will granny save me? Birth status,survival, and the role of grandmothers in historical Finland

Grandmothers play a crucial role in families enhancing grandchild wellbeing and survival but their effects can be context-dependent, and the children born in poor conditions are most likely to benefit from the investments made by helping grandmothers. In this study, we examined, for the first time, whether grandmothers' presence modified associations between adverse birth status and survival up to 5 years of age. In detail, we verified, whether (i) firstborns, (ii) twins, (iii) children born within 24 months after their sibling, and (iv) children followed by short interval (i.e. their younger sibling was born within 24 months) survived better when either their maternal, paternal, or both grandmothers were present. Moreover, we evaluated whether illegitimate children survived better when the maternal grandmother was present. We used an extensive and largely pre-industrial demographic dataset collected from parish population registers kept by the Lutheran Church of Finland from years 1730–1895. We show that although grandmother presence cannot mitigate adverse effects of many poorer birth conditions, grandchildren whose next sibling was born after a short interval survived better when the maternal grandmother was present. Taken together, these findings highlight an important role of grandmothers in compensating the mother's investment in the new baby, thus enabling overall faster successful reproductive rate of mothers. Whilst the opportunity for grandmothers to mitigate the risks of adverse birth statuses is limited, this study does show - through the beneficial effect on survival for those with a short subsequent birth interval - that grandmothers can increase their daughters' and their own reproductive success.     

Offspring production among the extended relatives of Samoan men and fa'afafine

Androphilia refers to sexual attraction to adult males, whereas gynephilia refers to sexual attraction to adult females. Male androphilia is an evolutionary paradox. Its development is at least partially influenced by genetic factors, yet male androphiles exhibit lower reproductive output, thus raising the question of how genetic factors underlying its development persist. The sexual antagonism hypothesis posits that the fitness costs associated with genetic factors underlying male androphilia are offset because these same factors lead to elevated reproduction on the part of the female relatives of androphilic males. Western samples drawn from low fertility populations have yielded inconsistent results when testing this hypothesis. Some studies documented elevated reproduction among the matrilineal female kin of androphilic males, whereas others found such effects in the paternal line. Samoa is a high-fertility population in which individuals reproduce closer to their maximum capacities. This study compared the reproductive output of the paternal and maternal line grandmothers, aunts, and uncles of 86 Samoan androphilic males, known locally as fa'afafine, and 86 Samoan gynephilic males. Reproductive output was elevated in the paternal and maternal line grandmothers, but not aunts or uncles, of fa'afafine. These findings are consistent with the sexual antagonism hypothesis and suggest that male androphilia is associated with elevated reproduction among extended relatives in both the maternal and paternal line. Discussion focuses on how this study, in conjunction with the broader literature, informs various models for the evolution of male androphilia via elevated reproduction on the part of female kin.     

Biogeographical and evolutionary importance of the European high mountain systems

Background

Menopause is a seemingly maladaptive life-history trait that is found in many long-lived mammals. There are two competing evolutionary hypotheses for this phenomenon; in the adaptive view of menopause, the cessation of reproduction may increase the fitness of older females; in the non-adaptive view, menopause may be explained by physiological deterioration with age. The decline and eventual cessation of reproduction has been documented in a number of mammalian species, however the evolutionary cause of this trait is unknown.

Results

We examined a unique 30-year time series of killer whales, tracking the reproductive performance of individuals through time. Killer whales are extremely long-lived, and may have the longest documented post-reproductive lifespan of any mammal, including humans. We found no strong support for either of the adaptive hypotheses of menopause; there was little support for the presence of post-reproductive females benefitting their daughter's reproductive performance (interbirth interval and reproductive lifespan of daughters), or the number of mature recruits to the population. Oldest mothers (> 35) did appear to have a small positive impact on calf survival, suggesting that females may gain experience with age. There was mixed support for the grandmother hypothesis – grandoffspring survival probabilities were not influenced by living grandmothers, but grandmothers may positively influence survival of juveniles at a critical life stage.

Conclusion

Although existing data do not allow us to examine evolutionary tradeoffs between survival and reproduction for this species, we were able to examine the effect of maternal age on offspring survival. Our results are consistent with similar studies of other mammals – oldest mothers appear to be better mothers, producing calves with higher survival rates. Studies of juvenile survival in humans have reported positive benefits of grandmothers on newly weaned infants; our results indicate that 3-year old killer whales may experience a positive benefit from helpful grandmothers. While our research provides little support for menopause evolving to provide fitness benefits to mothers or grandmothers, our work supports previous research showing that menopause and long post-reproductive lifespans are not a human phenomenon.     

Retrospective study of maternal HIV-1 and HIV-2 infections and child survival in Abidjan,C?te d'Ivoire.

OBJECTIVES--To compare the effects of maternal HIV-1 and HIV-2 infections on outcome of pregnancy, infant mortality, and child survival, and to measure serological concordance between mothers and children. DESIGN--Retrospective cohort study with cross sectional study of concordance for HIV antibodies. SETTING--Hospital, tuberculosis clinic, and maternal and child health centre in Abidjan, Côte d''Ivoire, west Africa. SUBJECTS--986 women who had had a total of 2758 pregnancies since 1980. The last born children of 194 of these women. MAIN OUTCOME MEASURES--Pregnancy outcomes; mortality for all children born since 1980; and outcome for last born children. Serological concordance between mothers and last born children. RESULTS--Women with HIV-1 and HIV-2 infections had higher rates of spontaneous abortion and stillbirth than uninfected women (86/769 in HIV-1 positive women, 48/421 in HIV-2 positive, 31/234 in dually reactive, and 96/1131 in uninfected). Compared with children born to uninfected mothers (mortality 10.3%), greater proportions of children of HIV-1 positive (20.6%) and dually reactive (20.3%) mothers had died; mortality in children of HIV-2 infected women (13.1%) was not significantly increased. Infant mortalities for the last born children of HIV-1 positive, dually reactive, HIV-2 positive, and seronegative women were, respectively, 133, 82, 32, and 40 per 1000 live births. Nine of 77 last born children of HIV-1 positive mothers were concordantly seropositive compared with none of 21 children of HIV-2 infected mothers. CONCLUSIONS--Maternal HIV-2 infection has less influence on child survival than infection with HIV-1, probably because of a lower vertical transmission rate.     

雌性黄山短尾猴回避近亲交配

本研究分别在交配期(2006年9月-2006年12月)和产仔期(2007年1月-2007年4月)对黄山短尾猴鱼鳞坑YA1群中5只雄猴和5只雌猴成年个体采用目标动物法、随机取样法和连续记录法记录行为参数。研究期间记录交配行为336例:母子交配0例;母系兄妹交配7例(占2.1%),其中强行交配4例;非亲缘关系交配329例(占97.9%),非亲缘关系交配频次显著高于亲缘关系。在交配期,雄猴对亲缘雌猴跟随、性检查频次均低于非亲缘雌猴,接近指数(PMI)在亲缘和非亲缘雌猴间无显著性差异;雌猴对亲缘雄猴交配拒绝率显著高于非亲缘雄猴,接近指数在交配期显著低于非亲缘雄猴,产仔期接近指数在亲缘和非亲缘雄猴间无显著性差异。尽管雄猴在交配选择上趋于避免与亲缘雌猴交配,但某些雄猴仍会主动对有亲缘关系的雌猴邀配或强行交配,雌猴则主动回避。这些结果表明:黄山短尾猴母系亲属间可以通过行为倾向抑制近亲交配发生,且雌猴更主动回避交配,支持了近交回避的双亲投资理论。     

Reproductive and socioeconomic determinants of child survival: confounded, interactive, and age-dependent effects.

Studies of infant and child mortality have evolved to distinguish between two sets of explanatory variables-factors related to reproductive or maternal characteristics and socioeconomic factors, generally described as characteristics of the family or household. Almost all multivariate analyses include variables from each of these two sets, but there has been little consideration of the relationship between them. We examine how these two sets of variables jointly affect mortality. We test first for confounded effects by examining socioeconomic effects while excluding and then including reproductive variables in nested multivariate models. Next, we look for age-dependent effects among the explanatory variables and find that reproductive and socioeconomic factors affect mortality at differing ages of children. Finally, we examine interactive effects of the two sets of variables. We conclude that the higher mortality observed among the low status groups is not a result of greater concentration of poor reproductive patterns in those groups. Instead, higher status groups probably have more resources available for combating the negative effects of the same high-risk reproductive patterns.     

Long-Term Trends in Matrilineal Inbreeding Among the Japanese Macaques of Arashiyama B Troop

In a long-term study of sexual behavior in Japanese macaques, we found that matrilineal inbreeding accounted for 2.9% of the copulations recorded for the Arashiyama B troop during 7 mating seasons between 1968 and 1984. Of the 906 copulatory dyads, 46 (5.1%) occurred among kin. Close matrilineal kin dyads (r = 1/2–1/8, 1.1% of the total of copulatory dyads) strongly avoided matrilineal inbreeding, but for remote kin dyads (r > 1/8, 4.0% of the total) the tendency was weaker in some years. Among the possible determinants of matrilineal inbreeding, we found that it tended to occur among younger and lower-ranking males as an effect of troop demographic changes. There is no significant association between female rank and matrilineal inbreeding. Our results are consistent with the hypothesis that different degrees of kin relatedness are discriminated by individuals with respect to mate choice.     

Flexible kinship: caring for AIDS orphans in rural Lesotho

HIV/AIDS has devastated families in rural Lesotho, leaving many children orphaned. Families have adapted to the increase in the number of orphans and HIV‐positive children in ways that provide children with the best possible care. Though local ideas about kinship and care are firmly rooted in patrilineal social organization, in practice, maternal caregivers, often grandmothers, are increasingly caring for orphaned children. Negotiations between affinal kin capitalize on flexible kinship practices in order to legitimate new patterns of care, which have shifted towards a model that often favours matrilocal practices of care in the context of idealized patrilineality.     

Covariates of child mortality in Mali: does the health-seeking behaviour of the mother matter?

This paper uses data from the 1995/96 Mali DHS survey to examine the importance of a wide range of socioeconomic, behavioural and biodemographic factors in the determination of child mortality in Mali, with a special focus on maternal education and behaviour. The central hypothesis of the study is that advances in maternal education would contribute little to child survival in settings such as Mali's urban and rural communities where progress in educational attainment is not matched with improvements in other aspects of socioeconomic development such as economic growth, job creation, financial security and public health and medical resources. Units of analysis are children born in the past 5 years to DHS respondents (women aged 15-45) who were married at the time of the survey. The Cox proportional hazards regression technique has been used to estimate the net effects of variables included as covariates. The findings indicate that the health-seeking behaviour of the mother matters more than maternal education in explaining the observed differences in infant and child mortality in Mali's urban and rural areas.     

Reproductive and socioeconomic determinants of child survival: Confounded,interactive, and age‐dependent effects

Abstract

Studies of infant and child mortality have evolved to distinguish between two sets of explanatory variables—factors related to reproductive or maternal characteristics and socioeconomic factors, generally described as characteristics of the family or household. Almost all multivariate analyses include variables from each of these two sets, but there has been little consideration of the relationship between them. We examine how these two sets of variables jointly affect mortality. We test first for confounded effects by examining socioeconomic effects while excluding and then including reproductive variables in nested multivariate models. Next, we look for age‐dependent effects among the explanatory variables and find that reproductive and socioeconomic factors affect mortality at differing ages of children. Finally, we examine interactive effects of the two sets of variables. We conclude that the higher mortality observed among the low status groups is not a result of greater concentration of poor reproductive patterns in those groups. Instead, higher status groups probably have more resources available for combating the negative effects of the same high‐risk reproductive patterns.     

Maternal factors and infant and child mortality in Bangladesh

Using data from The World Fertility Survey, this study shows that the length of the preceding birth interval was the most important maternal factor influencing infant and child mortality risks in Bangladesh. This was such a crucial factor that its effects remain unaltered whether or not the influences of mother's age at birth and birth order are controlled. Infant and child mortality in Bangladesh can be expected to decline considerably if successive births can be spaced by an interval of at least 1.5 years. Child spacing seems to be the major factor requiring program attention. The effects of mother's education and place of residence on infant and child mortality are independent of the effects of maternal age at birth, birth order, and the preceding birth interval. The higher survival chances of children of educated mothers resulted neither through the age at which childbearing started nor through birth spacing but are likely to be related to their smaller family size and to other non-maternal proximate determinants of early mortality.