Biology Magazine

Why the “us and Them” Mentality Evolved

Posted on the 13 August 2013 by Reprieve @EvoAnth

Humans have been living in large complex groups for millions of years, and flourishing as a result. This social environment has shaped the course of our evolution as much as any natural one, in particular how our psychology has evolved. For example, humans are highly susceptible to peer pressure, likely to ensure we do what the group wants and so don’t risk being thrown out of it. A human going solo would not survive for long (Hawkes et al., 1991).

Now new research has identified yet another aspect of human psychology that seems to have evolved to help us deal with living in social groups: dividing the world into an in-group and an out-group, and working extra hard to curry favour with the former. Although the habit of humans to break the world down into “us” and “them” has been known about for years (and often blamed for many sources of tension in the world) there has always been debate over whether it is an innate psychological tendency or something we are trained to do (van Vugt and Hardy, 2010).

After all, we’re exposed to loads of things that train us to split the world into in- and out-groups, from sports teams to countries to religions. But are they the source of this division, or simply the by-product of us naturally breaking the world down. This new research believes they’ve solved this mystery by investigating whether very young children (5 years old) also divide up the world like this.

First they gathered up a lot of children from various different day care centres so they wouldn’t know each other. They then dressed them up in either red or blue and put two of them in a room. One was given a set of stickers and asked to donate some to an unknown third child who would enter the room later, the other told to observe. If the observer was wearing the same color as the donater then they were much more generous, giving five times as many stickers to the unknown child (Engleman et al., 2013).

This is a similar to how adults behave in a similar situation, being more generous when watched by in-group members in an attempt to build a reputation with them (Reiss and Gruzen, 1976). However, since this study was dealing with children who have yet to fully mature psychologically (Wimmer and Perner, 1983) and haven’t been exposed to quite as many institutions trying to make us split the world up into “us and them.” As such this strongly indicates that they will not have been influenced by culture in quite the same way, suggesting that this behavior is at least partly biological and thus evolved.

Ordinarily speculating about the influence of evolution would be unjustified, it’s where evolutionary psychology often goes very wrong. However, this study identified an additional interesting effect that may shed light on the evolution of the “us and them” mentality.

The researchers repeated the experiment, but sometimes the children involved were told that the observer would then become the donater, and the donater would be the one relying on his charity to get stickers. When this was done the original donater would behave generously, regardless of whether the observer was wearing the right color or not (Engelman et al., 2013).

This suggests that they key motivation behind dividing the world up into in- and out-groups was reciprocity. You acted nicely towards members of an in-group because they were part of your group and thus you were more likely to encounter them later. As such, if you build up your reputation with them by being generous, they may be more likely to help you when you see them around town. So if you know a member of the out-group will be in a position where they could help you later, it pays to curate a reputation with them too.

Unfortunately this research alone is not enough to put this issue to bed. Speculation is not EvoPsych’s only problem, it also tends to extrapolate results from a small group of humans, claiming that the phenomena identified in them are present in all humans and thus innate and evolved. Whilst this research did involve children from several daycare centres, it’s still not enough to justify such extrapolation.

If these results are confirmed by further studies then this research could help us understand one of the biggest sources of tension in the world. Which will hopefully lead to a better future, as well as giving us a greater understanding of our past.


Engelmann, J. M., Over, H., Herrmann, E., & Tomasello, M. (2013). Young children care more about their reputation with ingroup members and potential reciprocators. Developmental Science.

Hawkes, K., O’connell, J. F., Jones, N. B., Oftedal, O. T., & Blumenschine, R. J. (1991). Hunting income patterns among the Hadza: big game, common goods, foraging goals and the evolution of the human diet [and discussion].Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences334(1270), 243-251.

Reis, H.T., & Gruzen, J. (1976). On mediating equity, equality, and self-interest: the role of self-presentation in social exchange.Journal of Experimental Social Psychology, 12, 487–503.

van Vugt, M., & Hardy, C.L. (2010). Cooperation for reputation: wasteful contributions as costly signals in public goods. Group Processes & Intergroup Relations, 13, 101–111.

Wimmer, H., & Perner, J. (1983). Beliefs about beliefs: Representation and constraining function of wrong beliefs in young children’s understanding of deception. Cognition13(1), 103-128.

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