The new study was inspired by work in chimpanzees that found their cooperation regularly breaks down. "Chimpanzees often compete over food, which prevents them from working together on a task, even if that's the only chance for them to get a reward" says Felix Warneken of Harvard University, a coauthor of the study. "So we were wondering if the same is true also in young children." He carried out the study with Karoline Lohse of the University of Göttingen and Alicia P. Melis and Michael Tomasello of the Max Planck Institute for Evolutionary Anthropology.
Other research in humans has suggested that young children might not be very good at sharing, but this has usually depended on asking the children what they'd do in hypothetical situations, or giving them one shot at dividing up resources.
For this study, the researchers wanted to take a more thorough look at how young children share, particularly in a situation where they had to work together for a common goal. They had pairs of children complete a task in which they had to collaborate to get a prize. The prize -- gummy bears, stickers, or other items -- was piled on a board with wheels inside a transparent box. If only one child pulled on a rope, the board wouldn't move, but if they pulled together, they could bring it toward them and reach the food or toys through windows in the transparent box. Sometimes there was only one window to reach through; sometimes there were two. But even when there was only one window, which meant that one child could have monopolized the prizes, the children almost always shared equally. Each pair of children was tested several times.
"We were surprised that this rule was so strict -- that equality was so strongly preferred," Warneken says. And the children shared virtually without conflict. "It was rarely the case that one took all the resources and the other kid had to say, 'Hey, that's not fair.'" Sometimes, if one child didn't take their half of the spoils immediately, the other would even point it out.
This helps explain how mutually beneficial arrangements evolve, Warneken says. It seems like they should show up everywhere -- if we cooperate, we're both better off. But in fact, even a species as similar to us as chimpanzees doesn't necessarily display that behavior. So, Warneken says, maybe what's missing from chimps -- and what humans have in abundance -- is the ability to get along with others.