Chimps Who Beat Kids in a Test of Rationality Reveal Humans' Selfish Side

Rationality may be considered a human virtue, but we’re not always so great at it. In a recent study, a team of scientists reached the unexpected conclusion that chimpanzees and young children are technically more rational than older children. Underlying this difference in behavior is a concept called social comparison, a feature of human social life that describes the tendency to understand ourselves in relation to others. Rationality is overrated; what humans really want is to come out ahead.

Earlier in January, in the Proceedings of the Royal Society B, a team of anthropologists and psychologists examined the manifestation of social comparison in an experiment in which individuals were given two options: a tray with three treats or a tray with nine treats. These trays came with a catch — if an individual chose the three-treat tray, they could walk away with two treats and a peer observing would get one. If an individual chose the tray with nine, they would get three treats while their peer would get six.

The latter choice, the scientists deemed, was the rational one: Choosing it still resulted in getting more treats, even if someone else got more than you. The team proceeded to give three groups the opportunity to choose: A group of chimpanzees (ranging in age from 8 to 37 years), a group of five- to six-year-olds, and a group of nine- to ten-year-olds.

The Max Planck Institute and Yale University scientists who conducted the experiments discovered that the vast majority of chimpanzees and children under 6 chose the tray with more treats on it — the rational choice. Meanwhile, the 9- and 10-year-olds consistently chose the tray with fewer treats: These kids, the team determined, were more concerned about fair play. Getting fewer treats was fine, as long as they didn’t get fewer than another kid.

The choices made by the older children is where social comparison comes in, fitting with previous research that found inequity aversion increases with age. To an extent, the scientists explain, social comparison-/based fairness has been proven to be an important psychological mechanism that underlies human patterns of cooperation. As humans evolved and developed the traits that allowed them to live in complex cultural groups, an insistence on fairness emerged as a means to keep these groups running.

Chimps, who share 98.8 percent of their DNA with humans and live in social groups, are not thought to engage in social comparison. This hypothesis was something the scientists wanted to test in this experiment, and it proved to still be elusive; chimpanzees were rational-maximizers, who cared less about having more than others just for the sake of it. The team explains how the complex dynamic of social comparison does and doesn’t play out in chimps:

“While social comparison underlies fairness, a hallmark of human social life which gives rise to a concern for equality, at the same time it manifests itself in more negative emotions such as envy and Schadenfreude. Chimpanzees might not demonstrate concern for equality, but neither is their behavior influenced by social comparison’s more self-centered expressions.”

What the scientists found here is that when kids reach the age of nine they become less like chimps — and more like competitive adults. That’s the darker side of social comparison: The willingness to reduce everyone’s payoff simply because it puts you on top. Sociality, the study concludes, is not always entwined with pro-sociality — and even if you’ve evolved to thrive in a group, you may still be looking out for yourself.