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1. Non-kin adoption in the common vampire bat

   https://doi.org/10.1098/rsos.201927  

   Razik, Imran; Brown, Bridget K.; Page, Rachel A.; Carter, Gerald G. (February 2021, Royal Society Open Science)

   Individual animals across many different species occasionally ‘adopt’ unrelated, orphaned offspring. Although adoption may be best explained as a by-product of adaptive traits that enhance parental care or promote the development of parental skills, one factor that is possibly important for the likelihood of adoption is the history of cooperative interactions between the mother, adopted offspring and adopter. Using 652 h of behavioural samples collected over four months, we describe patterns of allogrooming and food sharing before and after an instance of non-kin adoption between two adult female common vampire bats ( Desmodus rotundus ) that were captured from distant sites (340 km apart) and introduced to one another in captivity. The first female died from an illness 19 days after giving birth. The second female groomed and regurgitated food to the mother more often than any other group member, then groomed, nursed and regurgitated food to the orphaned, female pup. The substantial increase in alloparental care by this female after the mother's death was not observed among the 20 other adult females that were present in the colony. Our findings corroborate previous reports of non-kin adoption in common vampire bats and are consistent with the hypothesis that non-kin adoption can be motivated, in part, by a history of cooperative interactions. 

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2. Intergenerational Clustering of Under-Five Mortality: A Cohort Perspective in Low- and Middle-Income Countries

   https://doi.org/10.1215/00703370-11477436  

   Smith-Greenaway, Emily; Weitzman, Abigail; Lin, Yingyi; Huss, Katarina (July 2024, Demography)

   Abstract A burgeoning demographic literature documents the exceedingly high rates at which contemporary cohorts of women across the Global South experience the death of their children—even amid historic declines in child mortality. Yet, the patterning of maternal bereavement remains underinvestigated, as does the extent to which it replicates across generations of the same family. To that end, we ask: Are the surviving daughters of bereaved mothers more likely to eventually experience maternal bereavement? How does the intergenerational clustering of maternal bereavement vary across countries and cohorts? To answer these questions, we make use of Demographic and Health Survey Program data from 50 low- and middle-income countries, encompassing data on 1.05 million women and their mothers spanning three decadal birth cohorts. Descriptive results demonstrate that maternal bereavement is increasingly patterned intergenerationally across cohorts, with most women experiencing the same fate as their mothers. Multivariable hazard models further show that, on average, women whose mothers were maternally bereaved have significantly increased odds of losing a child themselves. In most countries, the association is stable across cohorts; however, in select countries, the risk associated with having a bereaved mother is shrinking among more recent birth cohorts. 

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3. The expendable male hypothesis

   https://doi.org/10.1098/rstb.2018.0080  

   Mattison, Siobhán M.; Quinlan, Robert J.; Hare, Darragh (September 2019, Philosophical Transactions of the Royal Society B: Biological Sciences)

   null (Ed.)

   Matriliny is a system of kinship in which descent and inheritance are conferred along the female line. The theoretically influential concept of the matrilineal puzzle posits that matriliny poses special problems for understanding men's roles in matrilineal societies. Ethnographic work describes the puzzle as the tension experienced by men between the desire to exert control over their natal kin (i.e. the lineage to which they belong) and over their affinal kin (i.e. their spouses and their biological children). Evolutionary work frames the paradox as one resulting from a man investing in his nieces and nephews at the expense of his own biological offspring. In both cases, the rationale for the puzzle rests on two fundamental assumptions: (i) that men are in positions of authority over women and over resources; and (ii) that men are interested in the outcomes of parenting. In this paper, we posit a novel hypothesis that suggests that certain ecological conditions render men expendable within local kinship configurations, nullifying the above assumptions. This arises when (i) women, without significant assistance from men, are capable of meeting the subsistence needs of their families; and (ii) men have little to gain from parental investment in children. We conclude that the expendable male hypothesis may explain the evolution of matriliny in numerous cases, and by noting that female-centred approaches that call into doubt assumptions inherent to male-centred models of kinship are justified in evolutionary perspective. This article is part of the theme issue ‘The evolution of female-biased kinship in humans and other mammals’. 

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4. Epigenetics, gene expression, and stress in mothers and offspring in the Democratic Republic of Congo: A biocultural investigation of the intergenerational effects of stress

   Mulligan CJ, Maisha FM (January 2019, American journal of physical anthropology)

   The field of social and behavioral epigenetics examines how social and behavioral experiences can cause epigenetically-driven changes in gene expression that in turn influence health and well-being. We work in the eastern Democratic Republic of Congo, where 20 years of conflict and post-conflict violence have subjected women to extreme stress and sexual violence. We collected blood samples from mothers and their offspring at birth, plus follow-up samples from offspring up to five years of age, in three cohorts (2010 cohort, n=25; 2013 cohort , n=103, 2015 cohort, n=77). Using DNA extracted from blood and placental samples, we assayed methylation using Illumina’s 450K and EPIC chips, telomere length, and gene expression using the ClariomS chip. We also collected ethnographic and survey data on maternal stress, newborn health outcomes, and cortisol from offspring saliva and hair samples. Using these data, we tested for associations among maternal stress, DNA methylation, gene expression, and offspring health outcomes. We find that epigenetic aging is accelerated in mothers relative to chronological age, but newborn epigenetic age appears unchanged. In contrast, telomere length is significantly shorter in offspring born to mothers with high levels of war stress, but this effect only emerges after birth. Analyses of epigenome and gene expression data are ongoing. Our study takes a biocultural perspective to understand the molecular, biological, and health effects of stress and violence, particularly from an intergenerational perspective. 

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5. Weak, but not strong, ties support coalition formation among wild female chimpanzees

   https://doi.org/10.1098/rstb.2021.0427  

   Fox, Stephanie A.; Muller, Martin N.; González, Nicole Thompson; Enigk, Drew K.; Machanda, Zarin P.; Otali, Emily; Wrangham, Richard; Thompson, Melissa Emery (January 2023, Philosophical Transactions of the Royal Society B: Biological Sciences)

   In social species, individuals may be able to overcome competitive constraints on cooperation by leveraging relationships with familiar, tolerant partners. While strong social ties have been linked to cooperation in several social mammals, it is unclear the extent to which weak social ties can support cooperation, particularly among non-kin. We tested the hypothesis that weakly affiliative social relationships support cooperative coalition formation using 10 years of behavioural data on wild female chimpanzees. Female chimpanzees typically disperse and reside with non-kin as adults. Their social relationships are differentiated but often relatively weak, with few dyads sharing strong bonds. Females occasionally form aggressive coalitions together. Three measures of relationship quality—party association, five-metre proximity and whether a dyad groomed—positively predicted coalitions, indicating that relationship quality influenced coalition partnerships. However, dyads that groomed frequently did not form more coalitions than dyads that groomed occasionally, and kin did not cooperate more than expected given their relationship quality. Thus, strong bonds and kinship did not bolster cooperation. We conclude that cooperative coalitions among female chimpanzees depend on social tolerance but do not require strong bonds. Our findings highlight social tolerance as a distinct pathway through which females can cultivate cooperative relationships. This article is part of the theme issue ‘Cooperation among women: evolutionary and cross-cultural perspectives’. 

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