In an earlier post, I explain why virtually all stereotypes are empirically true. Stereotypes come from the aggregation and generalization of the daily experiences of millions of people, so they cannot possibly fail to be true. Stereotypes are based on massive empirical data, and empirical data don't lie. However, I also explain that one of the very few stereotypes that are not empirically true is the aphorism "You can't judge a book by its cover." Contrary to popular belief, you can very accurately judge people's character just by looking at them.
There have been a large number of experiments conducted in recent years to show that altruists (people who tend to cooperate in situations where self-interested behavior might benefit them personally) and egoists (people who tend not to cooperate in such situations) genuinely look different, and people can tell them apart simply by looking at them. These studies show that people pay more attention to the faces of cheaters, and later remember their faces more accurately, even when they don't know who are cooperators and who are defectors. The latest in the series of such experiments has just been published in the September 2009 issue of the journal Human Nature, with the very descriptive title "Altruism Can Be Assessed Correctly Based on Impression."
The study, conducted by Ryo Oda of the Nagoya Institute of Technology and his colleagues, clearly demonstrates that you can judge a book by its cover. (Here is a picture of Professor Oda in Kenya, with a pair of baboons in the background, apparently about to fornicate.) In their study, a large number of male undergraduate students complete a self-reported altruism scale. Those in the top 10% on the altruism scores are designated as "altruists," and those in the bottom 10% are designated as "egoists." These "altruists" and "egoists" are then individually videotaped during a normal conversation with a blind confederate in a closeup shot. The first 30 seconds of the videotaped conversation are then shown to different groups of students at a university more than 800 miles away (in order to eliminate the possibility that the perceivers may personally know the targets). The video clips of the targets are shown to the perceivers without sound, to prevent the targets from betraying their level of altruism by verbal cues.
Their study shows that the perceives, when asked to estimate the targets' levels of altruism, can accurately guess who are altruists and who are egoists. Interestingly, even though perceivers who are themselves altruists tend to think that others are more altruistic in general than perceivers who are themselves egoists, both types of perceives can nonetheless accurately judge who are altruists and who are egoists among the targets. Surprisingly, men and women in their study are equally good at estimating the altruism level of total strangers. (There are theoretical reasons to believe that women are better judges of character than men in general.) Further, altruists are judged to be significantly more active, more generous, more responsible, friendlier, kinder, more extroverted, and as giving better impression than are egoists, but altruists are not judged to be more discreet, more hurried or more intelligent. Further analyses of Oda et al.'s data show that the key to detecting altruists is genuine smile, which is under involuntary control and is therefore difficult to fake. Altruists genuinely smile more frequently than egoists during natural conversations.
Oda et al.'s study is only the latest in the series of experiments which demonstrate that we can indeed judge a book by its cover. Nice, altruistic, and cooperative people look nice, altruistic, and cooperative; nasty, egoistic and uncooperative people look nasty, egoistic, and uncooperative. And we (both altruists and egoists, both men and women) have the capacity to tell them apart, after looking at them for only 30 seconds without sound! In retrospect, this should come as no surprise. We have been dealing with potential cheaters throughout evolutionary history, and being duped and deceived by them has always carried tremendous costs. In other words, the presence of cheaters has exerted strong selection pressure on our ancestors. It would be a miracle if a capacity to judge people's character based on their appearance did not evolve sometime during the course of human evolution.