The last thing you need if you're feeling rejected is to waste time pursuing friendships with people who aren't genuinely interested. That's according to Michael Bernstein and his colleagues, who say we've actually evolved a perceptual adaptation to rejection that helps prevent this from happening.
Bernstein's team provoked feelings of rejection in students by asking them to write about a time they felt rejected or excluded. These students were subsequently better at distinguishing fake from real smiles as depicted in four-second video clips, than were students who'd either been asked to write about a time they felt included, or to write about the previous morning.
"These results are among the first to show that rejection can lead to increases in performance at the perceptual level, provided that the performance supports opportunities for affiliation," the researchers said.
However, I wonder if this increased ability to detect fake smiles is as adaptive as the researchers imply. In the same way that unrealistically positive beliefs about the self can guard against depression, perhaps it would be more helpful to a socially excluded person to tone down their sensitivity to fake smiles. After all, just because a stranger gives you a fake smile doesn't mean they aren't a potential friend - they may just have had a bad day.
Michael J. Bernstein, Steven G. Young, Christina M. Brown, Donald F. Sacco, Heather M. Claypool (2008). Adaptive Responses to Social Exclusion: Social Rejection Improves Detection of Real and Fake Smiles Psychological Science, 19 (10), 981-983 DOI: 10.1111/j.1467-9280.2008.02187.x