Nature Genetics | Free Association

Chimpanzees are selfish, but children are kind

I pose an age-old question: what is it that makes us human? I think it depends who you ask. Ask a cognitive neuroscientist and they may say it’s our theory of mind, which is a fancy way of saying humans have empathy. Ask an evolutionary biologist and they will likely point out all the morphological traits that distinguish us from other primates, such as the large size of our cranial vaults or our opposable thumbs. Ask a psychologist and they may cite our conscience or our ability to use symbolism. But no matter who you ask, most would likely agree that our capacity for sharing resources and the social rules that regulate sharing are specific to human culture.

In a new study published in Nature,

Michael Tomasello and colleagues report a series of experiments in 2-3-year-old children and chimpanzees and conclude that 3-year-old children are more likely to equitably divide resources gained by collaborative activities compared to a non-collaborative situation. They further conclude that collaborative activity does not seem to influence sharing in chimpanzees.

It is known that 3- to 4-year-old children typically divide resources unequally and are more likely to maintain possession of any resources for themselves than share with others. However, as children approach five to seven years of age, they start to share resources more equitably. Tomasello and colleagues hypothesized that children might share a resource more equitably at an earlier age if they had to work collaboratively to attain it, compared to when resources are provided by adults (as resources usually are when children are 3-4 years old).

In this study, pairs of age-matched children were put in a room by themselves (after a demonstration phase) and exposed to a collaboration, no-work, or parallel-work condition. In the collaboration scenario, the children faced a rope attached to an enclosed apparatus. Pulling on the rope together would bring toys in the enclosed apparatus toward them, and the ‘lucky’ child would gain three toys, while the ‘unlucky’ child would gain one toy. In the no-work condition, the children entered the room with the toys already positioned in the end-state. The ‘lucky’ child shared the extra toy with the ‘unlucky’ child more often in the collaboration condition compared to the no-work condition. To control for the possibility that sharing was influenced by the fact that the collaboration condition required work, the authors also ran a parallel-work condition. Here, each child had to pull on their own rope to attain the toys. The authors still observed that the ‘lucky’ child shared toys with the ‘unlucky’ child more often in the collaboration condition compared to either the no-work or parallel-work conditions.

Next, the authors hypothesized that collaboration would not influence resource sharing in chimpanzees. They placed pairs of chimpanzees on opposing sides of an apparatus that required simultaneous pulling of a rope to move grapes to a see-saw that was accessible to both chimpanzees. The ‘lucky’ chimp attained 2 grapes and a chance to take the other grape, while the ‘unlucky’ animal received 1 grape and also had a chance to take the other grape. In the first study, the ‘unlucky’ chimp tipped the see-saw and took the other grape for itself in 63% of trials. The ‘lucky’ chimp never actively tipped the seesaw toward the unlucky animal. Next, the authors tried to encourage the ‘lucky’ chimp to share by disabling the seesaw to the ‘unlucky’ chimp. They noted that the ‘lucky’ chimp tipped the food to itself in 98% of cases, and found no difference in sharing in collaborative vs. control conditions.

This study demonstrates that humans as young as 2- to 3-years-old are able to recognize rewards attained through collaborative efforts and demonstrate a sense of “distributive justice.” Since chimpanzees do not require collaboration for acquisition of resources in the wild, the authors suggest that chimpanzees have not, as a species, developed this sense. This study provides evidence that a sense of “distributive justice” distinguishes humans from other primates and reinforces the notion that collaborative efforts played an important role in human evolution. And so I end with another question. Are humans inherently kind or selfish? I don’t think we know the answer to that question, but this study implies that for humans, evolution has favored the kind.