A well-known example of irrational decision-making people's tendency to overvalue the things they own (I would pay $1 for a coffee mug but will demand $5 for an identical coffee mug that happens to be mine). This bias of "the mind" is called the "endowment effect" and is often assumed to be universal (and therefore explained as the work of evolution). But in this paper Coren Apicella, Eduardo Azevedo, James Fowler, and Nicholas A. Christakis found that some people and some minds don't have this bias at all. Rather than being built-in to human nature, they write, the endowment effect may be a habit of mind that people learn in market-oriented societies. If that's true, it means that (for this trait at least) the hunter-gatherers described in the research were more rational before they were exposed to modern capitalism.
In any case, the other important lesson of this paper is that, as ever, theories about "the mind" shouldn't be based on tests run only on minds that are Western, Educated, Industrial, Rich and Democratic, or WEIRD. And that, more generally, it's always important to check one's assumptions about what is innate and universal in psychology. "Whenever a pattern of human behavior is widespread, there is reason to suspect that it might have something to do with our evolutionary history," a pair of biologists recently noted. True enough, but sometimes patterns of human behavior aren't as widespread as we want to believe, in our eagerness to spin a theory. (People have, in fact, tried to find a reason why the endowment effect must have evolved to be a part of every human psyche—for example, here.) The attractiveness of such theories should make everyone a little cautious about the generalizations on which they rest.