Instead, he prefers what he calls the “grizzly bear hypothesis” (and as if men did not have enough to be anxious about, this one will send us running for the Xanax). When a subordinate male grizzly mates with a female, he constantly swivels his head around looking for the nearby dominant male who will cut in, so to speak. So the subordinate males go for quickies, ejaculating as fast as possible. The dominant males can swagger in and take their time. “With whom would you orgasm?” Barash asks, evoking an image I’d rather not contemplate.

He thinks it’s possible that orgasm is a way for a woman’s body to tell her mind that she is copulating with a powerful, attentive, secure male. That means good genes. “Perhaps orgasm is an evaluation of a male, a way females inform themselves” of the kind of male they are with, he says.

And I thought it was my stock portfolio.  

3. Baffling breasts
Women have breasts, of course, to feed babies. But why do human females cart around prominent breasts even if they are not pregnant or lactating? Most other mammals don’t.

Unless a woman is lactating, or getting ready to, breast size is determined by how much fat a woman stores there. In a statement sure to make everyone feel good, Shlain argues that a “dog belly has no subcutaneous fat. We have the most of any land mammal.”

He says this fat serves the purpose of sexual arousal.

“When we stood up,” he says, referring to our early ancestors, “the anatomy of the pelvis changed. The vagina oriented itself more toward the front.” But this was a problem because most mammals, including primates, have sex doggie style. Hence the big red butts advertising “Sexy girl here!” meant to appeal to our visual sense. (Primates do not smell as well as, say, dogs.) So, since males began facing females for sex, the rough equivalent of big red butts “were transposed to the front of a woman” and became the breasts we know and love.

Not everyone buys it. “I do not find the butt-to-front theory convincing,” Rosenberg says, pointing out, as does Dettwyler, that breasts are not sex objects in many cultures, so it is hardly a universal human trait to obsess about them.

In most non-Western cultures, Dettwyler argues, “for adult men to suck on a woman’s breast is as bizarre as a bull nursing from a cow.” She also believes Western women have relatively large breasts because “we are overfed.”

Barash disagrees, citing several notions, such as the “Goldilocks hypothesis” (too small means she is too young and not fertile, too large and sagging means too old and not suitable for mating) and the “symmetry theory” (breasts are good for telling how symmetric, and therefore healthy, a woman might be).

But his favorite is the “deception hypothesis.” Our forefathers might have been fooled into thinking a woman with large breasts was a nursing superstar, when actually, those bosoms were just loaded with fat. So lured, men would provide food and attention and sex, which could explain the well known “boob-job-equals-5-carats” corollary. 

Breasts as a mating ruse? Bait? An anatomic Potemkin Village? Personally, I don’t care why we like them, but the evolutionary theories are fascinating even if nobody is sure of the answers.

And there are yet more female mysteries, including menstruation and the timing of menopause.

But even though science seems to understand a man's biology better than a woman's, based on what's known about males throughout the animal kingdom, there's another way of looking at all this.

"Females," says Rosenberg, "have departed more from the primitive” — which sounds like a nice way of telling me women are more highly evolved than men.

HARRUMPH!

Brian Alexander is a California-based writer who covers sex, relationships and health. Alexander, also a Glamour contributing editor, recently traveled around the country to find out how Americans get sexual satisfaction for the MSNBC.com special report "America Unzipped" and for an upcoming book for Harmony, an imprint of Crown Publishing.

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