We are better at spotting fake smiles when feeling rejected
  
 
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.
  
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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.http://dx.doi.org/10.1111/j.1467-9280.2008.02187.x
Author weblink:http://www.users.muohio.edu/claypohm/