The Great London:
Society

Sex equality in residential decision-making explains the unique social structure of hunter-gatherers, a new UCL study reveals.

Previous research has noted the low level of relatedness in hunter-gatherer bands. This is surprising because humans depend on close kin to raise offspring, so generally exhibit a strong preference for living close to parents, siblings and grandparents.

The new study, published today in Science and funded by the Leverhulme Trust, is the first to demonstrate the relationship between sex equality in residential decision-making and group composition.

In work conducted over two years, researchers from the Hunter-Gatherer Resilience Project in UCL Anthropology lived among populations of hunter-gatherers in Congo and the Philippines. They collected genealogical data on kinship relations, between-camp mobility and residence patterns by interviewing hundreds of people.

This information allowed the researchers to understand how individuals in each community they visited were related to each other. Despite living in small communities, these hunter-gatherers were found to be living with a large number of individuals with whom they had no kinship ties.

The authors constructed a computer model to simulate the process of camp assortment. In the model, individuals populated an empty camp with their close kin - siblings, parents and children.

When only one sex had influence over this process, as is typically the case in male-dominated pastoral or horticultural societies, camp relatedness was high. However, group relatedness is much lower when both men and women have influence - as is the case among many hunter-gatherer societies, where families tend to alternate between moving to camps where husbands have close kin and camps where wives have close kin.

First author of the study, Mark Dyble (UCL Anthropology), said: "While previous researchers have noted the low relatedness of hunter-gatherer bands, our work offers an explanation as to why this pattern emerges. It is not that individuals are not interested in living with kin. Rather, if all individuals seek to live with as many kin as possible, no-one ends up living with many kin at all."

Many unique human traits such as high cognition, cumulative culture and hyper-cooperation have evolved due to the social organisation patterns unique to humans.

Although hunter-gatherer societies are increasingly under pressure from external forces, they offer the closest extant examples of human lifestyles and social organisation in the past, offering important insights into human evolutionary history.

Senior author, Dr Andrea Migliano (UCL Anthropology), said: "Sex equality suggests a scenario where unique human traits such as cooperation with unrelated individuals could have emerged in our evolutionary past".

Source: University College London [May 15, 2015]

Long before the advent of social media, human social networks were built around sharing a much more essential commodity: food. Now, researchers reporting on the food sharing networks of two contemporary groups of hunter-gatherers in the >Cell Press journal Current Biology provide new insight into fundamental nature of human social organization.

The new work reveals surprising similarities between the Agta of the Philippines and Mbendjele of the Republic of Congo. In both places, individuals maintain a three-tiered social network that appears to buffer them against day-to-day shortfalls in foraging returns.

"Previous research has suggested that social networks across human cultures are structured in similar ways," says Mark Dyble of University College London. "Across societies, there appear to be similar limits on the number of social relationships individuals are able to maintain, and many societies are said to have a 'multilevel' structure. Our work on contemporary hunter-gatherer groups sheds light on how this distinctive social structure may have benefited humans in our hunting-and-gathering past."

While previous studies have identified similarities in social structure across hunter-gatherer populations, the researchers say that the new work is the first to explore how hunter-gatherers' distinctive, "multilevel" social organization structures social life and cooperation in important activities such as foraging and food sharing.

"No other apes share food to the extent that humans do," says Andrea Migliano, principal investigator of the Leverhulme Trust-funded Hunter-Gatherers Resilience Project. "Hunter-gatherers' multi-level social structure exists in different groups, to help regulate these cooperative systems. Furthermore, multi-level social structures regulate social rules, friendship and kinship ties, and the spread of social norms, promoting a more efficient sharing and cooperation. Sharing is a crucial adaptation to hunter-gatherers' lifestyles, central to their resilience -- and central to the evolution of mankind."

The Agta live in northeast Luzon, Philippines. Their primary source of protein is fish, supplemented by inter-tidal foraging, hunting, honey collecting, and gathering of wild foods. The Mbendjele live in an area spanning northern Republic of Congo and southern Central African Republic, where they hunt for meat in the forest. Both groups also trade wild-caught meat or fish for cultivated foods, including rice and manioc.

Dyble, Migliano, and their colleagues collected data on food sharing by living with the two communities for many months, making observations on how often households shared food with each other. From this they constructed social networks of food sharing.

"Although we had an idea of how camps split into food sharing clusters 'on the ground,' we were able to test these using algorithms which are able to identify sub-communities within the nine camps we studied," Dyble explains.

Their analysis showed that food sharing is closely related to social organization. In both communities, individuals maintain a three-tiered social network. First is their immediate household, most often consisting of five or six individuals, second is a cluster of three to four closely related households who share food frequently, and third is the wider camp.

"Despite being from different continents and living in very different ecologies, both groups of hunter-gatherers had a strikingly similar social organization," Dyble says.

"Cooperation and especially food sharing are essential for survival in a hunting-and-gathering economy," Dyble says. "The proverb that 'it takes a village to raise a child' is certainly true for hunter-gatherers, who, without food sharing to mitigate the day-to-day shortfalls in foraging, could simply not survive."

Dyble says that they now intend to explore the structure of other types of social networks in the hunter-gatherer communities, such as cooperation in childcare, and their overlap with food sharing.

Source: Cell Press [July 21, 2016]

Reciprocal food-sharing is more prevalent in stable hunter-gatherer camps, shows new UCL research that sheds light on the evolutionary roots of human cooperation.

The research explores patterns of food-sharing among the Agta, a population of Filipino hunter-gatherers. It finds that reciprocal food-sharing is more prevalent in stable camps (with fewer changes in membership over time); while in less stable camps individuals acquire resources by taking from others -- known as 'demand sharing'.

Exploring social dynamics in the last remaining groups of present day hunter-gatherers is essential for understanding the factors that shaped the evolution of our widespread cooperation, especially with non-kin.

The study, published in the Royal Society journal >Open Science, is the first to report a real-world association between patterns of cooperation and group stability.

First author of the study, Daniel Smith (UCL Anthropology), said: "Cooperation between unrelated individuals is rare in animals, yet extensive among humans. Reciprocity -- the principle of "you scratch my back, I scratch yours" -- may explain this non-kin cooperation, yet requires stable groups and repeated interactions to evolve.

"Our research shows that hunter-gatherer cooperation is extremely flexible -- reflecting either reciprocity or demand sharing depending on the frequency of repeated interactions between camp members."

The authors looked at two types of food-sharing data. Firstly, details of actual food-sharing from six Agta camps were examined to explore whether differences in camp stability predicted patterns of food-sharing. Secondly, games were also conducted in which individuals were asked to distribute resources between themselves and other camp-mates. These games were conducted with 324 Agta over 18 separate camps.

In one of the games, participants were shown their own picture, along with other randomly selected adults from camp. They were then given a number of small wooden tokens, each representing 125g rice, equal to the number of camp-mates' photos. Not every picture including the subject's could end up with rice on it, introducing a social dilemma regarding whether to share, as it would be impossible for everyone to receive rice. Participants then decided, token by token, whether to keep the rice for themselves, or to give to a camp-mate.

The results showed that, firstly, stable camps were more likely to display reciprocity in the actual food-sharing analyses. Patterns of food-sharing in unstable camps were not reciprocal, consistent with demand sharing, whereby individuals take resources from others rather than being given them. Secondly, individuals from more stable camps were increasingly likely to give resources to others and less likely to take resources in the games.

Despite differences in cooperation, individuals from both stable and unstable camps received resources from others. This distribution of resources among camp-mates is crucial for hunter-gatherers' survival. As foraging success is variable it is likely that, on any given day, an individual may return to camp with no resources. Food-sharing is therefore essential to reduce the likelihood of individuals going without resources for extended lengths of time.

Last author, Professor Ruth Mace (UCL Anthropology), added: "Food sharing and cooperation are at the centre of hunter-gatherers lifestyle. No other Apes share food or cooperate to the extent that humans do. A complex network of sharing and cooperation exists within camps and between camps in different hunter-gatherer groups, regulated by social rules, friendship ties, food taboos, kinship and supernatural beliefs. Sharing is a crucial adaptation to hunter-gatherers' lifestyles, central to their resilience -- and central to the evolution of humankind."

Source: University College London - UCL [July 13, 2016]