IF YOU have ever sat alone in a bar, depressed by how good-looking everybody else seems to be, take comfort-it may be evolution playing a trick on you. A study just published in Evolution and Human Behavior by Sarah Hill, a psychologist at the University of Texas, Austin, shows that people of both sexes reckon the sexual competition they face is stronger than it really is. She thinks that is useful: it makes people try harder to attract or keep a mate.

Dr Hill showed heterosexual men and women photographs of people. She asked them to rate both how attractive those of their own sex would be to the opposite sex, and how attractive the members of the opposite sex were. She then compared the scores for the former with the scores for the latter, seen from the other side. Men thought that the men they were shown were more attractive to women than they really were, and women thought the same of the women.

Dr Hill had predicted this outcome, thanks to error-management theory-the idea that when people (or, indeed, other animals) make errors of judgment, they tend to make the error that is least costly. The notion was first proposed by Martie Haselton and David Buss, two of Dr Hill's colleagues, to explain a puzzling quirk in male psychology.

NGF level was significantly higher (p<0.001) in the subjects in love [mean (SEM): 227 (14) pg/ml] than in either the subjects with a long-lasting relationship [123 (10) pg/ml] or the subjects with no relationship [149 (12) pg/ml]. Notably, there was also a significant positive correlation between levels of NGF and the intensity of romantic love as assessed with the passionate love scale (r=0.34; p=0.007). No differences in the concentrations of other NTs were detected. In 39 subjects in love who—after 12–24 months—maintained the same relationship but were no longer in the same mental state to which they had referred during the initial evaluation, plasma NGF levels decreased and became indistinguishable from those of the control groups.