A study published in the current issue of Evolution and Human Behavior shows us, once again, that people should respect stereotypes and the sub-rational gut.
The authors found that college students could look at photos of sex offenders for only two seconds and then predict whether the person was a violent or non-violent offender.
Analysis revealed that students were focusing on signs of testosterone and masculinity (e.g., heavy brows, apparent physical strength, youth).
Women were more likely than men to perceive the the offenders to be violent. The authors concluded that results support the view that humans have evolved the ability to quickly size up the physical threat of another person because heavy costs would accompany the inability to do so, and that women would be particularly likely to perceive a man as a physical threat because of the risk of sexual violence.
These stereotypes find their way into fiction all the time. Marv in Sin City (shown above), played by Mickey Rourke, might be a good example from the past few years. Someone who looks like Marv might actually be a pussycat, but I'm not going to call him an asshole to his face.
UPDATE: Two other points: 1) Non-violent sex offenders are typically depicted as small, weak weasels. Think of the pedophile played by Jackie Earle Haley in Little Children. 2) The study deliberately avoids race, stating that research indicates a bias against photos of non-whites. But the study's findings can easily be used to explain the fear that people feel toward blacks. African Americans are perceived as having higher levels of testosterone as indicated by physical traits. Size and apparent physical strength; hard muscle tone; narrow hips and broad shoulders; long limbs--all are masculine characteristics.
John Manning in The Finger Book also claims that dark skin is a sign of testosterone. Men are darker than women, and he presents the case that abundant melanosomes and melanin inhibit the invasion of bacteria and fungi through the outer surface of the skin and are found in people whose immune systems are weakened by high levels of testosterone.
Nurturists would explain the perceived dangerousness of blacks as a myth taught to kids by prejudiced parents and peers. But Asians are racial outsiders: why don't whites have any fear of them? Why are blacks afraid of blacks? Why are race-virgin immigrants--white or Asian--afraid of blacks?