Spite emerges in childhood, alongside more pro-social habits like cooperation and sharing, according to a recent psychological study.

The study, conducted by a postdoctoral fellow at Yale and two psychology professors from Harvard and Boston University, shows that spite, not frustration, drives children ages four to nine to sacrifice Skittles to prevent their partners from getting greater amounts of Skittles.

“If you think about a rational economic model, it’s not ideal that someone has more [Skittles than the other person], but one [Skittle] is better than nothing, so they should accept the offer even though they’re at a disadvantageous position,” said lead author and post-doctoral fellow Katherine McAuliffe. “What we found is that people aren’t happy with that distribution. They would rather have nothing in many cases than deliver a better reward to their partner.”

McAuliffe said that one way to interpret this behavior is to infer that children are being spiteful. She defined spitefulness as a willingness to inflict a cost on another even if it has no benefit to, or even hurts, the actor.

While people have thought of spite as a motivational force among children before this study, this research is unique in that it eliminates punishment and frustration as potential motivations. For each round of the experiment, one volunteer was chosen to be the actor, and he or she was confronted with different situations.

In the first situation, one actor was to choose whether he wanted to get one Skittle and his partners to get four, or whether he wanted both to get zero Skittles. In the second situation, his partner was automatically given four skittles, and the actor chose to either get one Skittle or zero Skittles. If the actor were to reject Skittles regardless of whether or not it meant that his partners would also get zero skittles, then his motivation was probably frustration, McAuliffe said. But if the children only chose to sacrifice the Skittle when it meant that their partners would also get zero skittles, the motivation would be spite. The majority of children ages 4–9 were more likely to reject one Skittle when it deprived their partner of Skittles, leaving spite as the primary motivation. Adults did not exhibit spiteful motivation.

The study gives valuable insight into how and when competitiveness and conceptions of equity develop in children, said Yale assistant professor of psychology and neurobiology Steve Chang. However, he added that the data on adults are less trustworthy, as adults probably cared less about Skittles than do children. He would like to see the same experiment done with something like money that would matter to adults. It would be interesting to see if the data change depending on if and to what extent the participants know each other, he added.

McAuliffe acknowledged that the adults could also have reputational concerns arising from social norms that may not have as great of an influence on children. She suggested that a way to test this in the future is to compare adults and children from different cultures. McAuliffe added that they are looking into accounting for the general need for whatever reward is being used. For example, before an experiment with Skittles, those administering the experiment could record subjects’ hunger level. Finally, she is planning on looking into third party intervention to see if people like to prevent inequity even when their own resources are not at stake.

According to a Washington State University study, younger adults are more spiteful than older adults.