Source: Pixabay

People are pretty good at sharing when they are cooperating. People working will give each other food and drinks as the task goes on. They share the profits from joint ventures. Even kids will make sure that everyone gets a turn at games to make sure the entire group is enjoying the activity.

A paper in the July, 2016 issue of Psychological Science by Alicia Melis, Patricia Grocke, Josefine Kalbitz, and Michael Tomasello explored when this ability develops. In addition, they addressed the question of whether this ability is something that is relatively unique to humans by looking at a similar task in chimpanzees.

To study kids, the researchers tested a group of 3-year-olds and a group of 5-year-olds. They sat kids on opposite sides of a device like the one in the figure here. There was a car on a track in the center aisle that could be moved if both children pulled a string on the same end of the track. That is, they had to cooperate in order to get the car to move.

Source: Association for Psychological Science

After being trained on how to use the device, it was configured like in the figure. The golden balls contained stickers. Kids this age love stickers, so they are a great reward to use in studies. The child gets the sticker only if the ball falls in one of the outer holes. If it falls in the inner hole, it is lost. On the experimental trials, the device was set up so that only one child would get a sticker on each trial. The question was whether kids would develop a strategy to share rewards.

The five-year-olds were quite good at this task. They tended to play the game so that both children got a fair number of stickers over the course of the game. They would talk to each other, and the child who had not gotten the sticker on one trial often asked to get the sticker on the next trial. Most of the pairs developed a strategy to alternate back-and-forth with rewards.

The three-year-olds were not so good. They did not really learn the strategy to alternate. They also talked to each other, but were quite likely to ask to get a sticker right after a trial in which they got one. This suggests that the ability to share rewards in a systematic way develops some time between the ages of 3 and 5.

What about the chimps?

They used a similar device (also shown in the figure). For them, the rewards were food. They were trained to cooperate in pulling the strings using trials in which both chimps got food when they pulled the same string. Then, for the test trials, the device was set up so that only one chimp would get food on any given trial.

The chimps acted a lot like the 3-year-olds in the study. They often cooperated so that one chimp got food, but they were not particularly systematic in how the food rewards were distributed. They did not alternate turns like the 5-year-olds. Indeed, the one pair of chimps that shared most did something like alternating for the first several trials and then one chimp got most of the rest of the rewards over the rest of the study.

This kind of turn-taking is important for complex group problem solving. It is hard to keep people motivated to participate in a task if they are not getting anything out of it. Distributing rewards in a task in a fair manner helps to keep people motivated to continue working. It looks like kids understand that by the age of five and will spontaneously develop a strategy to keep everyone engaged.

Chimps do some reciprocal rewarding in the wild. They will groom each other, for example. For chimps, this kind of turn-taking is probably learned specifically for a particular domain (like grooming) rather than as a general problem solving strategy. In contrast, 5-year-olds adapt to a novel environment fairly quickly and find an equitable way to distribute rewards.