The idea that some men could be more predisposed than others towards violent acts like rape is a horrifying thought, but in a philosophical inquiry, we don't shy away from an argument simply because the conclusion is unsavory.
When Randy Thornhill and Craig Palmer released their A Natural History of Rape: Biological Bases of Sexual Coercion (MIT Press, ISBN: 0262201259) in 2000, people across the country went absolutely ape shit over what they thought the book was trying to espouse. The authors sought to explain why rape occurs (and continues to occur, throughout millennia of human evolution), and although information in itself can never be evil, many attributed terrible motives to the duo's research.
Similar publications soon surfaced, including the articles "Rape as Adaptation" (Nature #404, March 2000) and "Darwinians Look at Rape, Sex, and War" (American Scientist #88, July-August 2000). All seemed to suggest the same thing.
The literature argued, simply enough, that in most cases, men raped for sex, not for power, and a predisposition towards rape could very well have been (and, in fact, probably was) genetically "ingrained" in some men's brains through traditional Darwinian Natural Selection.
And boy did those claims open up a powder keg.
The crux of most people's concerns was simple: there doesn't appear to be a very large leap to be made between discovering that some individuals are more predisposed to rape than others and using said information as a basis to "explain away" a rapist's guilt.
After all, the majority of rapes are acquaintance or "date" rapes, and so we can surmise that many of these rapes occur in the heat of passion: the woman says no, and the man (who is typically stronger than his mate, and is thus in a position to force his will upon her) continues anyway. Surely, said those troubled by Thornhill's discovery, if we find an evolutionary or genetic component that increases a man's proclivity towards rape, then he's not entirely responsible for that rape, and is thus absolved of some (or all) of his guilt.
But this is one of those times that Hume's Naturalistic Fallacy comes in handy. Simply because X is true, it does not follow that X is morally right or wrong. Just because a person is more apt to rape than others, it does not logically imply that his act cannot be judged immoral.
Consider the kleptomaniac. He or she has a terrible compulsion to steal, something our society deems both immoral and illegal. But do we allow the kleptomaniac to steal anyway, saying simply, "Well, he's sick, he has a compulsion, and so therefore, his actions are somehow less immoral than any other thief?" Certainly not! We seek help for the kleptomaniac, we hope to learn what causes his compulsion so we can prevent it in others, and we never accept his disease as an excuse for him to break the law.
Similarly, rape can never (and will never) be justified by any type of "psychological proclivity" or predisposition. First (assuming materialism, which most ethicists do), we must admit that each and every one of us is but a spectacular combination of cells, genes, atoms, and other matter. We make decisions based on our genetics, based on our past experiences, and based on personalities we have developed over our lifetimes. For this reason, we are who we are, and any genetic predisposition is as much a part of us as the way we smile or our favorite flavor of ice cream.
Every minute of every day offers a different choice for us to make. Some choose to act unethically, while others do not. Still others (more than we'd like to admit, I'm sure) are tempted to act unethically, to make a mad dash towards the front of the store with a couple dozen Playstation games shoved down our pants, or something like that. But the majority of us quell those immoral temptations because, despite our predisposition to go after what we want, we bow to both the legal and moral consequences of hurting others, of harming society, etc. And regardless of whether I have a genetic predisposition that causes me to intensely enjoy playing Grand Theft Auto, I would fully expect to pay the social and legal consequences should I try to shoplift a copy.
In the end, the debate boils down to one major question: Are some people more predisposed than others to use violence to obtain sexual gratification AND if they are, then is it unfair to hold those people responsible for their actions when they succumb to their compulsions?
The first part of this query is a question of fact--and the answer appears, at least on some level, to be "yes." Feminists (of which I consider myself one) found this scary because it appeared that if the first half of the statement was true, then it logically entailed the second portion. They worried: "If some people are more likely to rape, then doesn't that excuse them (at least a little bit) when they do so?"
The best response from scientists (including the late Harvard paleontologist Stephen Jay Gould) was quite simple, indeed:
Do not confuse a "proclivity" or a "predisposition" with "determinism" and "predestination."
Whether you have an urge to steal, an urge to rape, or simply an urge to stray from your diet, at some point, you are the one making the decision. If something about your genetic makeup makes you especially tempted to do something, then we should feel pity for you and try to give you all the help we can--but when you act on that temptation, when you chose to hurt another human being, you have exercised your free will, you have made a decision, and for that, you should (and will) be held morally accountable.
So, in retrospect, the concept that Thornhill and Palmer posited very much deserved our attention. (Thanks to HerMan for bringing up the topic in he first place.) Their data sparked an unintended debate about whether rape is "okay" (which is silly, because we all know it is not), but, more importantly, it gave us new insight into our genes, our past, and how they all combine to make us who we are today.
And, never wasting an opportunity to insert a cheesy link when I can: Knowing is half the battle.