Current social networks may have been present in the earliest modern humans

New research provides insight into the evolution of cooperation, and shows …

Kate Shaw Yoshida – Jan 26, 2012 12:30 pm | 15

A member of the Hadza identifies her social network for researchers. Credit: Photograph by Coren Apicella

If you ever sit back and wonder what it might have been like to live in the late Pleistocene, you’re not alone. That’s right about when humans emerged from a severe population bottleneck and began to expand globally. But, apparently, life back then might not have been too different than how we live today (that is, without the cars, the written language, and of course, the smartphone). In this week’s Nature, a group of researchers suggest that we share many social characteristics with humans that lived in the late Pleistocene, and that these ancient humans may have paved the way for us to cooperate with each other.

Modern human social networks share several features, whether they operate within a group of schoolchildren in San Francisco or a community of millworkers in Bulgaria. The number of social ties a person has, the probability that two of a person’s friends are also friends, and the inclination for similar people to be connected are all very regular across groups of people living very different lives in far-flung places.

So, the researchers asked, are these traits universal to all groups of humans, or are they merely byproducts of our modern world? They also wanted to understand the social network traits that allowed cooperation to develop in ancient communities.

Of course, the researchers couldn’t poll a group of ancient humans, so they had to find a community living today that has a lifestyle that closely resembles those of people who might have lived 130,000 years ago. They chose the Hadza, a group of hunter-gatherers that live in Tanzania and are very insulated from industrialization and other modern influences. The Hadza community functions much like ancient hunter-gatherer groups did, by cooperating and sharing resources like food and child care. Hadza society is organized into camps, which are taken up and abandoned regularly; the makeup of each camp also changes often, with individuals leaving one camp to join another.

The researchers visited 17 Hadza camps and surveyed 205 adults. First, they looked at individuals’ donations of honey sticks to other community members. They also asked questions like, “With whom would you like to live after this camp ends?” From the answers, the researchers constructed a model of the Hadza social network.

Many features of the hunter-gatherer network are very similar to those of modern, industrialized communities. Those who live farther away from each other are less likely to name each other as friends. Individuals who name more friends are also named more frequently by others, even among people they did not claim as their friends. People who resemble each other in some physical way tend to be connected as well; for Hadza people, similarity in age, body fat, and handgrip strength increases the likelihood of friendship.

There are also several features of the Hadza social network that may facilitate extensive cooperation. People that cooperate (in this case, by donating more honey sticks) are connected to other cooperators, while non-cooperators tend to be connected to each other. This type of clustering allows for cooperators to benefit from others’ large donations and increase in the population.

Evolutionary biologists have predicted that, for cooperation to evolve and spread, there should be more variance in cooperative behavior between groups than within groups. This is another example of clustering, and it allows for differences in the productivity and fitness of groups with different cooperation levels. And indeed, in Hadza society, there is more variance in cooperation between different camps than within camps.

From these results, two things are clear; first, that many of the universal characteristics of modern social networks also hold true for the Hadza, suggesting that these traits may have also governed the social networks of ancient humans. Second, several social features that have been predicted to facilitate the evolution and spread of cooperation are present in Hadza communities.

Clearly, ancient societies likely differed from the Hadza in many ways, but this community of hunter-gatherers may be as close as we can now get to the structure and characteristics of extinct human communities. Cooperation is one of the most heavily researched, yet poorly understood aspects of human life, and this research gives us insight into the type of community in which this phenomenon could have evolved and spread.

Nature, 2012. DOI: 10.1038/nature10736 (About DOIs).