Is human cooperativity an outcome of competition between cultural groups?

A study by ASU researchers looks at how culture may have fueled our capacity to cooperate with strangers

February 4, 2020

It may not always seem so, but scientists are convinced that humans are unusually cooperative.

Unlike other animals, we cooperate not just with kith and kin, but also with genetically unrelated strangers. Consider how often we rely on the good behavior of acquaintances and strangers — from the life-saving services of firefighters and nurses, to mundane activities like our morning commute and queueing at the airport check-in counter. Of course, we encounter people who cheat, disregard the welfare of others and engage in cronyism and nepotism. But we tend to perceive these behaviors as deviant, whereas in most animal societies these behaviors are the gold standard. person meeting with a group of people Former ASU postdoctoral researcher Carla Handley meets with a Turkana community group. Download Full Image

The hotly contested issue is why we are the famed cooperators of the animal kingdom. The answer is thought to be some characteristic that is exaggerated in humans compared to other animals: language, intelligence, culture, large-game hunting or our very needy children. Teasing apart how these traits influenced the evolution of cooperation has been challenging and has led to a proliferation of theories — and acrimonious debates — that emphasize one or other of these characteristics.                                                                                              

A study by Arizona State University researchers Carla Handley and Sarah Mathew published in Nature Communications provides some insight on this issue by pinpointing how culture may have fueled our capacity to cooperate with strangers.

The researchers empirically tested — and confirmed — predictions of a controversial theory referred to as cultural group selection theory. The idea is that culturally different groups compete, causing the spread of traits that give groups a competitive edge. Cooperation is exactly such a trait — costly for individuals, but advantageous for groups. Handley was a postdoctoral researcher with ASU at the time of study, and Mathew is assistant professor in the School of Human Evolution and Social Change and research affiliate with the Institute of Human Origins.

During the second half of the 20th century, biologists famously discredited the idea that selection could act on groups. They found that, typically, groups are not different enough from each other for selection to act on. Because individuals migrate, over time migration makes the composition of groups similar. Group-beneficial behaviors like cooperation therefore lose out.

The above concern may not apply, however, for behaviors that are culturally, rather than genetically, transmitted. When people migrate, they can, through social learning, culturally acquire the behaviors that are popular in their new surrounding. Thus, cultural groups can remain different, even if people move a lot. This means that selection can act on groups, and group-beneficial behaviors like cooperation can flourish.

"People have the intuition that being cultural helps us cooperate. What we are showing is that culture allows groups to be different and, therefore, to compete. It is this group competition — ironically — that sculpted our cooperativity,” said Mathew. 

To evaluate this theory, Handley and Mathew examined cultural variation and cooperation among Kenyan pastoralists. They sampled 759 individuals from nine clans spanning four ethnic groups — the Borana, Rendille, Samburu and Turkana — all of who practice semi-nomadic subsistence pastoralism in the arid savanna of northern Kenya. These groups compete intensively among each other for pasture, dry-season water wells and livestock, including through lethal cattle raids. The researchers found that, as predicted, cultural practices and beliefs were substantially variable between populations. Ten percent to 20% of the observed cultural variation was between competing groups. In contrast, typically less than 1% of genetic variation is between groups. This indicated that there is potential for cultural group selection to occur.

Carla Handley meeting with assistants

Postdoctoral researcher Carla Handley's "research office" in the field.

Next, they examined who people cooperate with and found that cooperation is indeed directed toward cultural ingroup members. People feel obliged to cooperate with strangers, as long as they share their cultural values, beliefs and norms with those people. Such culturally parochial cooperation is to be expected if competition between cultural groups influenced the evolution of cooperation.

“This study is unique as an empirical field test of cultural group selection by examining how cooperation operates between and within four distinct ethnolinguistic groups,” Handley said. “Taking a step back, it may also contribute to a reframing of conflict discourse in small-scale societies where cooperative action has been severely underrepresented and ‘illegitimate’ violence is regarded as the status quo.”

The findings caution that although humans are hypercooperative, our evolved cooperative dispositions are still limited in their scale, thus proving challenging for solving global-scale problems. Innovative thinking is necessary if we are to save ourselves from climate change, pandemics, or — who knows? — aliens.

Julie Russ

Assistant director, Institute of Human Origins


ASU anthropologist explores warfare as a form of cooperation

April 22, 2015

While many view warfare as a breakdown between societies, Arizona State University anthropologist Sarah Mathew views it as an outgrowth of cooperation.

Instead of focusing on warring factions, she considers that each side in a war is composed of people who hold the same ultimate goal and work together to achieve it. Download Full Image

Mathew studies the pastoral societies of East Africa to understand what bonds people in cooperative endeavors that can produce dangerous, often fatal, consequences. Most of her work revolves around the Turkana of Kenya, with whom she spent 15 months conducting fieldwork.

“These societies maintain high levels of social order and justice within the tribe without formal institutions, such as centralized governments and court systems, yet they also engage in lethal intertribal warfare,” she said.

Among the Turkana, half of adult male mortality is due to intertribal warfare, whereas only one percent can be attributed to interpersonal violence.

War parties average 300 warriors, and many are strangers. Armed with assault rifles, they travel up to 60 miles to steal cattle, raid villages or exact vengeance for previous raids.

During her time with the Turkana, Mathew interviewed 120 warriors who had participated in recent raids against a neighboring tribe. She followed that up with a survey of 300 community members that gauged their reactions to violations of local cultural norms.

Her results suggest that cultural norms promote behaviors that benefit the tribe, even when they are not in an individual’s best interest. Violations of norms generate moral judgments and lead to social sanctions that range from refusal of assistance to the administration of collective corporal punishment. The consequences motivate people to abide by the local norms, including norms related to violence.

Taking the research to the next level

Most research to date on human cooperation has been done on Western, educated, industrialized, rich and democratic populations. Mathew believes that advancing the study of the evolution of cooperation – and warfare – requires opening up the research to include the spectrum of cultures.

She also believes that harnessing the capacity for cooperation even further – to include those who fall outside the groups with whom we normally cooperate – is key to solving the problem of warfare.

“To accomplish this task,” Mathew said, “we need a more detailed understanding of the extent and scale of humans’ evolved prosocial and moral dispositions.”

Mathew recently became one of 32 inaugural Carnegie Fellowship winners, bringing her $200,000 to expand her work by launching two studies under the title “Is the Cultural Boundary Also the Moral Boundary?”

Other awardees of the Carnegie Fellowship included professors from Harvard University, MIT and and Standford University. (The full list of winners can be found here.)

Mathew's proposed research will focus on two areas. First, what are the social boundaries of people’s moral and cooperative dispositions? This issue is paramount because some theories of the evolution of human cooperation predict that the social boundary will be defined by the cultural or ethnic boundary.

Second, Mathew will attempt to determine whether there are consistent cross-cultural patterns in the psychological costs of killing in warfare.

On the latter subject, she is specifically concerned with a complicated question: Do cultural norms promoting lethal violence conflict with an evolved moral psychology that is averse to committing violence?

The Carnegie funding will allow Mathew to develop a data collection scheme to evaluate whether PTSD exists in warriors who have participated in intertribal warfare and if there is a systematic aversion to killing in combat.

“Sarah’s work is important because it will help us understand the nature of war over the broad sweep of human history and because it can illuminate many conflicts in the world today,” said noted cultural evolution pioneer Robert Boyd, who nominated Mathew for the Carnegie award.

Understanding the motivation and cost of warfare

While experiments reveal that people are motivated to sanction unfair behavior, the scale is not known. Mathew hopes to learn if people sanction unfair behavior only within their local community or if they extend sanctions to a larger cultural group or beyond the cultural group boundary.

Using economic experiments and vignette studies, she will explore how Turkana individuals judge and impose sanctions on a person who acts unfairly against a close associate, and how the response varies based on social distance.

What she discovers could lead to a wide variety of outcomes, from a better understanding of culturally inherited norms, values and beliefs to more effective treatment options for post-traumatic stress disorder.

Though young in her career, Mathew – an assistant professor in the School of Human Evolution and Social Change in the College of Liberal Arts and Sciences – is already a well-known expert in her field.

Last year, she shared the ASU Gammage stage with Steven Pinker, Richard Wrangham, Erica Chenoweth, Adrian Raine and John Mueller as part of an ASU Origins Project Great Debate on Transcending Our Origins: Violence, Humanity and the Future.

She also co-chaired a roundtable discussion at an American Anthropological Association meeting wherein ethnographers working among different warring pastoral societies in East Africa shared observations that pertain to this issue.

Unlike some of her peers, who believe that cultural differences birth insurmountable obstacles, Mathew operates from a more hopeful platform. She offers instances that bridge cultural divides to create cooperation, such as donations in the wake of natural disasters, trade groups, and yes, warfare.

She proposes that morality is the solution to violence and self-interested actions that harm others. Within this framework, the problems of today stem from the limited scale of morality that people extend only to members of their own family, ethnic group, political party, nation or religion.

As an example, Mathew points to nation states that typically condemn and punish internal homicide but allow – and even promote – killing during times of war.

“Nation states are able to solve many public good problems within their boundaries but have been unable to tackle global warming, which requires cooperation among multiple nation states,” she said. “Thus, it is crucial to understand the extent and scale of human prosociality in order to know how the moral sphere can be scaled up to solve critical global problems.”

Thanks to the Carnegie Fellowship, and an earlier award to the Institute of Human Origins from the John Templeton Foundation, Mathew will continue to build out her research into how humans – the sole species able to cooperate in large groups of unrelated, unfamiliar individuals – came to exploit that trait to destroy their own kind.

Rebecca Howe

Communications Specialist, School of Human Evolution and Social Change