Humans are much more inclined to cooperate than are their closest evolutionary relatives. The prevailing wisdom about why this is true has long been focused on the idea of altruism: we go out of our way to do nice things for other people, sometimes even sacrificing personal success for the good of others. Modern theories of cooperative behavior suggest that acting selflessly in the moment provides a selective advantage to the altruist in the form of some kind of return benefit.
A new study published by Current Anthropology offers another explanation for our unusual aptitude for collaboration. The authors of the study argue that humans developed cooperative skills because it was in their mutual interest to work well with others—indeed ecological circumstances forced them to cooperate with others to obtain food. In other words, altruism isn't the reason we cooperate; we must cooperate in order to survive, and we are altruistic to others because we need them.
Previous theories located the origin of cooperation in either small group settings or large, sophisticated societies. Based on results from cognitive and psychological experiments and research on human development, this study provides a comprehensive account of the evolution of cooperation as a two-step process, which begins in small hunter-gatherer groups and becomes more complex and culturally inscribed in larger societies later on.
The authors premise their theory of mutualistic cooperation on the principle of interdependence. They speculate that at some point in our evolution, it became necessary for humans to forage together, which meant that each individual had a direct stake in the welfare of his partners. In this context of interdependence, humans evolved special cooperative abilities that other apes do not possess, including dividing the spoils fairly, communicating goals and strategies, and understanding one's role in the joint activity as equivalent to another's. Good partners—who were able to coordinate well with their fellow foragers and would pull their weight in the group—were more likely to succeed.
As societies grew in size and complexity, their members became even more dependent on one another. In what the authors of this study define as a second evolutionary step, these collaborative skills and impulses were developed on a larger scale as humans faced competition from other groups. People became more "group-minded," identifying with others in their society even if they did not know them personally. This new sense of belonging brought about cultural conventions, norms, and institutions that incentivized and structured feelings of social responsibility.
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Tomasello, Michael, et al. "Two Key Steps in the Evolution of Human Cooperation: The Interdependence Hypothesis." Current Anthropology 53:5.