Thanks to Mike McCullough, a professor of psychology and religious studies at the University of Miami, for sending us his latest thoughts on sex differences in revenge (which also appear on his own blog and The Huffington Post):

A lipstick-adorned pit bull who hunts big game and shoots wolves from an airplane.
Unless you've been in a coma for the past month, you've probably noticed that the McCain campaign has put quite a bit of effort into portraying Senator John McCain's running mate as, umm, comfortable with the tools of aggression.
The evident appeal of the "Palin the Hunter" meme resonates with something else I've heard quite a bit recently: the claim that women are much more vengeful than men are. As you might know, I recently wrote a book about revenge, so I've gotten to hear a lot of different people's opinions on the subject, but until the past couple of months, I'd never heard so many people—mostly women, in fact—make this particular pronouncement with such conviction. In light of all the attention that the "guns and ammo" section of Gov. Sarah Palin's CV has received in the past few weeks, I just had to figure out where the "women are more vengeful than men" meme originated.
It turns out that it came from Patricia Cohen's New York Times piece, "Calculating Economics of an Eye for an Eye." Cohen was reporting on a recent research paper by Louisiana State University economist Naci Mocan which seemed to show that this is the case. At first glance, it seemed like a reasonable thing to conclude from Mocan's clever study, but honestly, women more vengeful than men? I had my doubts. Now that I've read Mocan's study myself, I'm even more skeptical. So before this becomes the next great urban myth about women (remember when we learned that single women over 40 stood a greater chance of being killed by a terrorist than finding a husband?), I thought I'd set the record straight.
In Mocan's massive survey of almost 90,000 people from 53 different countries, respondents were asked to recommend an appropriate sentence for a young man who has been convicted of burglary for the second time. (This time around, he has stolen a TV.) Respondents who recommended jail time were then asked to recommend how much time he should serve (from a month or less to life).
Mocan reasoned that the desire for revenge would show up as the excess amount of punishment recommended by respondents who had recently been burglarized themselves (about 7 percent of the sample) in comparison to people who had not been burglarized: Revenge, as Mocan observed, can only be executed by someone who has been wronged. He went on to discover that recent experience with being burglarized was linked to an 85 percent larger increase in the amount of punishment that women recommended than in the amount of punishment that men recommended. In other words, recent victimization changed women's judgments more dramatically than it changed men's judgments. And it was on this basis that Mocan concluded that females are the more vengeful sex.
But hang on: Why interpret this excess preference for stern punishment among burglarized women as the desire for revenge? Why not interpret it as the fear of revictimization? Which sex, do you suppose, would be more fearful of having a man break into their homes (remember, our hypothetical villain has stolen a television)? If it's the fairer sex, as I'd surmise, then the previously victimized women's elevated responses here may reflect not an elevated desire to return harm for harm, but rather, an elevated desire to keep criminals behind bars so that they're less likely to invade people's homes. We just can't be sure from the facts at hand.
A second problem: This study looked at people's guesses about how they would act in a hypothetical situation (prescribing a sentence for a hypothetical crime)—not how they actually responded to a choice with real consequences (as when a jury has to impose a sentence on a real criminal). Researchers have made careers out of showing how bad people are at these sorts of conjectures about their own behavior. If you're interested in people's surmises about their revenge behavior, then by all means, study their professed responses to hypothetical victimization scenarios. But if you're interested in what people actually do when they're wronged, ignore the conjecture and watch real behavior instead.
Speaking of behavior, the third reason to doubt that women are more vengeful than men is the mountain of behavioral research contradicting it. Consider this study from a couple of years ago—also reported in The New York Times—which showed that men had higher activation in brain areas associated with the anticipation of reward than women did when they watched someone who had previously harmed them experience physical pain. Conversely, women experienced higher activation in areas associated with empathy than men did in this situation. These sex differences suggest that men find enjoyment in seeing their provocateurs suffer, whereas women are pained by it.
Consider also this research on retaliatory homicides in St. Louis, Missouri. The researchers found that women committed about 10 percent of the nonretaliatory homicides, but only 4 percent of the retaliatory homicides. Sure, men do almost all of the killing in this world, but when it comes to revenge murders, they've practically got a monopoly.
Or how about this extensive review of laboratory experiments, which shows that men respond with more aggressive retaliation than women do when someone has done something nasty to them?
And what about anthropologists' studies of revenge around the world, such as Christopher Boehm's descriptions of the strong sexual division of labor in the blood feuds of tribal Montenegro, or Roger Gould's historical work on vendettas in 19th-century Corsica? Most of these studies show that it's quite rare for women to become actively involved in seeking revenge, although they often play important roles as goads to men who might otherwise lose their resolve to go forward with their bloody plans. Revenge, the anthropologists tell us, is (mostly) man's work.
Don't get me wrong—I liked Mocan's study in many ways and I'm glad to get my hands on it. But women more vengeful than men (i.e., pit bull plus lipstick = hockey mom)? Sure; it's one of those annoying little ideas that sticks in your head, and that can get your presidential ticket a little more attention, too, but as a legitimate statement about human nature and real behavioral differences between the sexes? Thanks but no thanks.