Why do men fixate on one body part?

While it is common to hear a man describe himself as an "ass man" or a "tit man," one never hears a woman describe herself similarly. 

Women tend to have what Freud described as a "polymorphously perverse" sexuality that can accommodate more variation: their sexuality can seemingly adapt to the desires of their partner. They care more about the personality of their mate, which is -- speaking evolutionarily -- at it should be. And they do not limit their attractions to one body part. I have yet to overhear a woman say, "I gotta admit, I'm pretty much of an ass woman," or, "I'd have to call myself a dick girl."

As women will tell you, theirs is the more humane, more humanitarian approach to mate selection. (They don't focus on something superficial like a body part; they just want a man with money.)

Men, on the other hand, tend to reduce women to their body parts. And they tend to get fixated. Rex Ryan, the New York Jets coach, suffered some embarrassing publicity last week when it became obvious from a film he had taken of his wife (in which he focused on her feet, and asked to touch them) that he is a foot fetishist. This particular fetish is probably rarer than it once was. It used to be that during the Victorian era, when women's feet were the one exposed part of their bodies, men would thrill to the sight of them and thus get fixated.

There was no voluntary component to this; men just become fixated with all the foresight and planning that a baby duck employs when it becomes fixated on its mother. Nor is there any morality involved: none of us has any control over whom or what we are attracted to.

I have a friend who is an obvious breast man. He focuses on that one feature to the point where all else is essentially irrelevant. I once said to him, "I could hang a pair of double D's on the back of your Mercedes and you'd probably do the tailpipe." He snorted in grudging acknowledgment. (He and I liked distinctly different types, which made him an ideal companion way back when.)

But why would evolution have made us this way? There doesn't seem to be any benefit. A man less finicky about having that one body part meet his standards would have more reproductive success. Similarly, a man attracted to a wide variety of women would seemingly have more options available. Yet almost all men have a certain type they are most attracted to, be that blonde or brunette, thin or voluptuous.

I haven't yet been able to come up with a good evolutionary reason as to why this should be so. For men to have one type -- and then to have certain standards for one aspect of that one type, further decreasing their pool of eligible prospects -- would seem self-defeating.

If you can think of a good reason why nature would have constructed us this way, please let me know.