As it turns out, humans possess the ability to tell who's a criminal and who's not simply by looking at them because criminals look different from noncriminals.

I have repeatedly emphasized the fact that virtually all "stereotypes" are empirically true. If they weren't true, they would not be stereotypes in the first place. To my knowledge, all of the very, very few stereotypes that are not empirically true, for some reason, have to do with people's appearance. Hence, it is not true that beauty is in the eye of the beholder, and it is not true that beauty is only skin-deep.

Another "stereotype" about physical appearance that is not empirically true is "you can't judge a book by its cover." In previous posts, I have explained that women can tell which men would make good fathers and which men would make bad fathers simply by looking at them. And people can tell who is and who is egoistic simply by looking at a 30-second video clip without sound.

So, contrary to popular belief, you can assess people's character and by simply looking at them. Nice people look nice, and nasty people look nasty, and it appears that humans have innate psychological mechanisms to tell them apart. Now, in a truly groundbreaking study, recently published in the Journal of Social, Evolutionary, and Cultural Psychology, Jeffrey M. Valla, Stephen J. Ceci, and Wendy M. Williams of Cornell University show that people can tell criminals and noncriminals apart simply by looking at their still photos. Criminals, it appears, look different from noncriminals.

In their experiments, Valla et al. show pictures of the faces of 32 young Caucasian men in their 20s, without scars, tattoos or excessive facial hair, all in neutral expressions. Sixteen of them are convicted criminals, and the other sixteen are not. Valla et al. simply ask their experimental participants to indicate how likely they think it is that each man is a certain type of criminal (murderer, rapist, thief, forgerer, assailant, arsonist, and drug dealer) on a seven-point Likert scale from 1 = extremely unlikely to 7 = extremely likely. Their results from two experiments consistently show that individuals can tell who is a criminal and who is not, by indicating that they believe the actual criminals have higher probability of being a criminal than actual noncriminals.

However, their results also show that individuals cannot tell what type of criminals they are. While Valla et al. are initially puzzled by this finding, it is actually consistent with what we know from . As I explain in an earlier post, criminals do not specialize. Men who commit one type of crimes are more likely to commit other types of crimes. (Remember O. J. Simpson?) Even though, for their experiments, Valla et al. carefully select pictures of criminals who are convicted of only one type of crimes, in empirical reality, there are no men who are only murderers (and do not and will not commit other types of crimes) or men who are only thieves (and do not and will not commit other types of crimes). Given time, some men would commit other types of crimes. In empirical reality, there are men who commit (all types of) crimes, and there are men who do not. And Valla et al.'s experiments show that individuals can tell them apart because the two types of men look different.

There is one seemingly anomalous finding in their paper. In both experiments, women are unable to spot rapists. Women consistently rate convicted rapists to be less likely to be criminal than not only other types of criminals but noncriminals as well! While this may be initially puzzling, upon further reflection, it makes perfect sense, as Valla et al. explain in their paper. In order to be a successful rapist, the man has to be able to fool the woman and earn her trust initially. Men who "fit the bill" by looking like a rapist or otherwise criminal and dangerous would not be able to do that. They would not be able to get close enough to the women to rape them. This may be why women, but not men, are unable to spot rapists, even though women are equally good as men at spotting other types of criminals.