Hunter-Gatherer children's close-proximity networks: Similarities and differences with cooperative and communal breeding systems.

Among vertebrates, allomothering (non-maternal care) is classified as cooperative breeding (help from sexually mature non-breeders, usually close relatives) or communal breeding (shared care between multiple breeders who are not necessarily related). Humans have been described with both labels, most frequently as cooperative breeders. However, few studies have quantified the relative contributions of allomothers according to whether they are (a) sexually mature and reproductively active and (b) related or unrelated. We constructed close-proximity networks of Agta and BaYaka hunter-gatherers. We used portable remote-sensing devices to quantify the proportion of time children under the age of 4 spent in close proximity to different categories of potential allomother. Both related and unrelated, and reproductively active and inactive, campmates had substantial involvement in children's close-proximity networks. Unrelated campmates, siblings and subadults were the most involved in both populations, whereas the involvement of fathers and grandmothers was the most variable between the two populations. Finally, the involvement of sexually mature, reproductively inactive adults was low. Where possible, we compared our findings with studies of other hunter-gatherer societies, and observed numerous consistent trends. Based on our results we discuss why hunter-gatherer allomothering cannot be fully characterised as cooperative or communal breeding.

Sedentarization and maternal childcare networks: role of risk, gender and demography.

Women cooperate over multiple domains and while research from western contexts portrays women's networks as limited in size and breadth, women receive help, particularly with childcare, from a diverse range of individuals (allomothers). Nonetheless, little exploration has occurred into why we see such diversity. Wide maternal childcare networks may be a consequence of a lack of resource accumulation in mobile hunter-gatherers-where instead households rely on risk-pooling in informal insurance networks. By contrast, when households settle and accumulate resources, they are able to retain risk by absorbing losses. Thus, the size and composition of mothers' childcare networks may depend on risk-buffering, as captured by mobile and settled households in the Agta, a Philippine foraging population with diverse lifestyles. Across 78 children, we find that childcare from grandmothers and sisters was higher in settled camps, while childcare from male kin was lower, offering little support for risk-buffering. Nonetheless, girls' workloads were increased in settled camps while grandmothers had fewer dependent children, increasing their availability. These results point to gender-specific changes associated with shifting demographics as camps become larger and more settled. Evidently, women's social networks, rather than being constrained by biology, are responsive to the changing socioecological context. This article is part of the theme issue 'Cooperation among women: evolutionary and cross-cultural perspectives'.

Children are important too: juvenile playgroups and maternal childcare in a foraging population, the Agta.

Non-maternal carers (allomothers) are hypothesized to lighten the mother's workload, allowing for the specialized human life history including relatively short interbirth intervals and multiple dependent offspring. Here, using in-depth observational data on childcare provided to 78 Agta children (a foraging population in the northern Philippines; aged 0-6 years), we explore whether allomaternal childcare substitutes and decreases maternal childcare. We found that allomother caregiving was associated with reduced maternal childcare, but the substitutive effect varied depending on the source and type of care. Children-only playgroups consistently predicted a decrease in maternal childcare. While grandmothers were rarely available, their presence was negatively associated with maternal presence and childcare, and grandmothers performed similar childcare activities to mothers. These results underscore the importance of allomothering in reducing maternal childcare in the Agta. Our findings suggest that flexibility in childcare sources, including children-only playgroups, may have been the key to human life-history evolution. Overall, our results reinforce the necessity of a broad conceptualization of social support in human childcare. This article is part of the theme issue 'Multidisciplinary perspectives on social support and maternal-child health'.

Learning to Be an Orangutan-Implications of Life History for Orangutan Rehabilitation.

Orangutans depend on social learning for the acquisition of survival skills. The development of skills is not usually assessed in rescued orphans' pre-release. We collected data of seven orphans over an 18-months-period to monitor the progress of ontogenetic changes. The orphans, 1.5-9 years old, were immersed in a natural forest environment with human surrogate mothers and other orphans. Social interactions deviated significantly from those of wild mother-reared immatures. Infants spent more time playing socially with peers, at the expense of resting and solitary play. Infants were also more often and at an earlier age distant from their human surrogate mothers than wild immatures are from their biological mothers. We found important changes towards an orangutan-typical lifestyle in 4- to 7-year-old orphans, corresponding to the weaning age in maternally reared immatures. The older orphans spent less time interacting with human surrogate mothers or peers, started to use the canopy more than lower forest strata and began to sleep in nests in the forest. Their time budgets resembled those of wild adults. In conclusion, juvenile orphans can develop capacities that qualify them as candidates for release back into natural habitat when protected from humanising influences and immersed in a species-typical environment.

Fake twins? Two cases of intensive allomaternal care by female Japanese macaques before and after their own partum.

Allomaternal care is widely observed among primate species. Although diverse allomothering behavioral repertoire and types of caretakers have been reported, it remains unclear what social or physiological conditions may trigger such care in each individual. For a better understanding of mechanisms that give rise to allomaternal care in primates, more observational reports are needed with information on social or physiological conditions of caretakers. Here I report two cases of intensive allomaternal care in two different populations of Japanese macaques (Macaca fuscata). The two adult females provided intensive allomaternal care including carrying, grooming, and nursing towards others' infants. Their allomaternal care began 20 or 29 days prior to their own partum and lasted for 84 days at the most. This study firstly showed that nursing forms part of the allomothering behavioral repertoire, and allomaternal caretakers can be individuals that are prior to the time of their own partum in Japanese macaques. Their intensive allomaternal care may stem from their good nutritional conditions, increased concentrations of several hormones, or disappearance of the newborn infants' biological mothers.

Evolutionary determinants of polycystic ovary syndrome: part 2.

Polycystic ovary syndrome (PCOS) is a prehistoric complex genetic trait, perhaps dating back at least 50,000 years. The disorder also represents an evolutionary paradox, demonstrating clear reproductive disadvantages (i.e., lack of evolutionary fitness), albeit persisting tens of thousands of years. Here we examine possible explanations for this paradox. We evaluate a variety of possible benefits accruing to women in ancestral populations who possessed this trait, including considerations of whether dramatic changes in environment and lifestyle from the ancestral past to the contemporary present have altered the selection dynamics operating on the trait. Putative benefits include metabolic functioning, immune system dynamics, patterns of child-rearing and mothering, reproductive longevity, in utero or childhood survival, and musculoskeletal advantages. However, there is limited evidence that the persistence and relative homogeneity in the prevalence of PCOS can be accounted for by direct positive selection. Rather, PCOS evolution has likely been driven by nonadaptive evolutionary mechanisms, including genetic drift due to a serial founder effect and population balance due to sexually antagonistic selection. Ultimately, insights into the evolutionary origins of PCOS will emerge through the study not only of unique characteristics of affected individuals and their environments butalso through a broad consideration of the potential adaptive and beneficial aspects of vulnerability to the disorder, importantly including examination of populations whose fertility, disease load, and diet resemble those of ancestral humans.

A unique case of extra-group infant adoption in free-ranging Angola black and white colobus monkeys (Colobus angolensis palliatus).

Infant adoption has been reported in a variety of primate taxa both in captive and natural settings. Adoption by females may be adaptive by increasing inclusive fitness via shared genes between adoptive mother and adoptee or by providing valuable maternal practice which, in turn, may increase the female's future reproductive success. Others have argued that adoption may be non-adaptive and the result of a general attraction toward infants. Our study examines a unique case of adoption by an adult female Angola black and white colobus monkey (Colobus angolensis palliatus) who adopted an extra-group infant alongside her own biological infant. We compare infant behaviors and mother-infant interactions between biological infant and adoptee and then compare both biological infant and adoptee behavioral profiles to those of infants under normal circumstances. Data were collected from July 2014 to June 2015 on three habituated groups in the Diani Forest of Kenya. Scan sampling and pooled data were used to create daily and monthly behavioral profiles for the biological infant and adoptee, as well as a mean monthly profile of four infants under normal circumstances. Data include time spent (1) clinging to mother/adoptive mother, (2) clinging to another individual, (3) behaving independently, and (4) behaving in close proximity to mother/adoptive mother. Initially, the adoptee struggled to achieve behavioral profiles consistent with those of the biological infant and normal colobus infants of the same age as he spent significantly more time moving independently and significantly less time clinging to the adoptive mother. After the mysterious death of the biological infant in mid-January 2015, the adoptee assumed a behavioral profile similar to that of infants under normal conditions. This case does not support adaptive hypotheses for adoption (i.e., inclusive fitness or learning to mother). Instead, because the biological infant died, possibly due to the presence of the adoptee, we argue that this case of infant adoption was non-adaptive. Ultimately, this adoption appears to have been an outcome of the adoptee's persistent desire to be cared for and the female's strong propensity to engage in allomaternal behavior.

Girl helpers and time allocation of nursing women among the Toba of Argentina.

In this paper we outline the activities of young girls in a Toba community of northern Argentina and examine the effect of girl helpers on time allocation of nursing women. Activity budgets were obtained for 41 girls aged 3 to 15 using spot observations. Girls spent substantial portions of observations engaged in helping behaviors. Individual values varied with age, anthropometric characteristics, and birth order. Activity budgets of 21 nursing women were obtained through focal observation sessions. Women living in households with girls aged 7 to 15 allocated 17% less time to domestic work and 9% more time to socializing during afternoon observation sessions. For nursing women in this community, direct childcare (provided by the infant's own mother) seemed to be a priority. Living with a girl helper did not have any measurable effect on the frequency or duration of nursing, or on the time that women spent caring for their infants. Based on these findings, hypotheses are outlined for future work on the effect of girl helpers on women's fertility.

Infant kidnapping and co-mothering in Japanese macaques.

The fatal kidnapping of a Japanese macaque infant is described. Kidnapping was followed by a long period (10 weeks) of co-mothering. Quantitative recording showed that both the biological mother (a 8-year-old, low-ranking, multiparous female) and the kidnapper (a 4-year-old, high-ranking female with no maternal experience) displayed an affectionate style of mothering and never responded negatively to the infant's demands for contact. Given the large maternal investment on the part of the kidnapper, we suggest that the fatal outcome for the infant was not the result of reproductive competition. © 1993 Wiley-Liss, Inc.

Lactation and care for unrelated infants in forest-living ringtailed Lemurs.

An adult female ringtailed lemur (Lemur catta) known not to have been pregnant showed spontaneous lactation in response to twin infants born to an unrelated female. The females had met only 7 months earlier, when they and two other unrelated adult females were released from separate locations in a forest enclosure to form a new social group. Three months after release, an adult male from an adjacent enclosure gained access to the new group for 1 day, the day of one female's estrus. No males had access to the females throughout the remainder of the breeding season. Within 2 weeks of the birth of the twins, one of the other adult females began carrying the infants frequently, typically one at a time. All three females were checked for lactation when the infants were two months old. Both their mother and the unrelated adult who had been carrying the infants were producing milk. The third adult female, who never carried either infant, had no milk. The third adult female, who never carried either infant, had no milk. This female, however, like the two maternal females, frequently attacked unfamiliar immigrating adult males when the males approached the infants. Potential implications of these observations concerning the social organization of ringtailed lemurs are discussed.

Fatal intragroup kidnapping in yellow baboons.

The fatal kidnapping of a 5-day-old baboon (Papio cynocephalus) in Amboseli National Park, Kenya, is described. Although pulling and rough handling of primate infants by nonmothers are frequently observed, records of fatal intragroup kidnappings are rare. In the instance described here, the mother, a healthy, primiparous female, did not retrieve the infant from the kidnapper, a higher-ranking juvenile female of the same group, until he died 3 days later, presumably from starvation or dehydration. This incident is compared with other fatal intragroup kidnappings in nonhuman primates and related to adaptive interpretations.