Yeah, the headline says "Why...", but the article doesn't actually explain why. There is some guesswork about the reason, but that seem to be independent of the

Yeah, the headline says "Why...", but the article doesn't actually explain why. There is some guesswork about the reason, but that seem to be independent of the experiment - you don't need brain scans to be able to make wild guesses about the evolution of a certain behavior. Brain scannings can't explain behavior, just as heightened heart rate is not an "explanation" for love or anger.