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Human beings are a social species. As a result, much of your behavior is affected by what other people are doing. You are more likely to exercise if you hang out with other people who exercise. You are more likely to smoke if you spend time with other smokers. You are more likely to succeed in school if your friends are also doing well in school.

Some of these effects come from the way people choose the groups they belong to. If academic achievement is important to you, then you may look to be with other people with the same values. Some of it also reflects goal contagion. When you see someone engaging in an activity, it makes you more likely to want to do the same thing.

Does mere membership in a group matter? To what degree are these behaviors affected just by your belief that you are part of a particular group? And, while we are at it, is this just something that happens to adolescents and adults, or is the behavior of younger children affected by the groups they belong to?

These questions were explored in a paper in the May 2018 issue of Psychological Science by Sabine Doebel and Yuko Munakata.

These studies used the classic marshmallow task as a measure of . In the marshmallow task, a 3 to 4-year-old is seated before a marshmallow on a plate. The experimenter tells the child that they can eat the marshmallow, but if they wait while the experimenter leaves the room and gets another one, they can have two marshmallows when the experimenter gets back. The length of time the child waits before eating the marshmallow is a measure of self-control. The experimenter stays out of the room for 15 minutes, so the maximum amount of time a child has to wait is 15 minutes.

In one study, the children were assigned to one of three groups. In all groups, participants were told that they are now a member of the green team. They are given a green shirt to wear and shown pictures of other members of the green team. They are also shown pictures of a second group of children with yellow shirts on, who are on the yellow team.

In the control condition, children are not given any other information about the green and yellow teams.

In the Green-waits condition, children are told that members of both teams did the marshmallow test and that the members of the green team all waited for the experimenter to return, while the members of the yellow team did not.

In the Yellow-waits condition, children are told that members of both teams did the marshmallow test and that the members of the yellow team all waited for the experimenter to return, while the members of the green team did not.

In this study, children in the Green-waits condition waited much longer (and were about twice as likely to wait the full 15 minutes) than children in the Yellow-waits condition or the control condition. So, believing that you are part of a group that has self-control affects your performance in the marshmallow task.

A second study in this paper ran the Green-waits and Yellow-waits conditions again and observe the same pattern of results. In addition, children in this study were told about two other children who were not part of a team. One child waited for the experimenter to return before eating a marshmallow, while the other at the marshmallow before the experimenter returned. The children were asked several questions to express how much they liked each child.

The children in the Green-waits condition were more likely to prefer the child who waited for the experimenter to return than the children in the Yellow-waits condition. This finding suggests that children come to value a behavior that distinguishes their group from the other group.

This finding is interesting because it adds a nice wrinkle to the influence of group membership on behaviors that require self-control. It suggests that just having an as a member of a group can affect self-control and that this can happen even in fairly young children.