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Well, I have some terrible news for 99 percent of us never destined to make People's Most Beautiful issue and thus get to be featured in essay one. This news is so terrible that it's even been reified with a cover story in Newsweek. But first, a Martian joke:

So the Martians finally come to Earth and they turn out to be great folks. Earthlings and Martians hit it off, sit around for days talking about politics, the weather on Mars and Earth, sports, what really happened with Elvis....Eventually, both the earthlings and Martians feel comfortable enough to work up the nerve and ask the other folks what they're really curious about — "So how do you guys reproduce?"

It's decided to have a demonstration. The Martians go first. Four of them stand on top of each other, make whirring mechanical sounds, lights go off on their foreheads, smoke and bells, and...suddenly, a new Martian pops out.

"Fabulous, just fabulous, love the concept," say the earthlings. Then it's our turn. A suitable volunteer couple has been found, a bed cleared, and the couple goes at it while the Martians stand around taking souvenir photos. The pair finishes in a sweaty heap.

"Great, that was terrific, very novel," enthuse the Martians, "but one thing...er...where's the new earthling?"

"Oh, that," they are answered. "That happens nine months from now."

And the Martians ask, "So why were they in such a rush at the end?"

So why are we in such a rush at the end? We animals will swim upstream and leap over dams, will spend hours butting heads with other antlered beasts, will laugh at someone's stupid jokes, all for the chance to mate, to get into that special circumstance where we are in such a rush at the end.

What is it that drives us to do so? Is it for the good of the species? Nah — that style of thinking went out with Marlin Perkins. How about its being for the good of the individual? "By mating as frequently as possible, you maximize the number of copies of your genes in the next generation and thereby enhance your reproductive success in the general population pool." Yeah, right — how many animals bring evolutionary-biology textbooks to bed with them? Option three: Because it feels good. Of course.

What we have here is a dichotomy between the distal and proximal explanations for the same behavior. Distal: the long-term, underlying explanation for why something happened. Proximal: the short-term, nuts-and-bolts explanation. For example, a female primate gives birth to an infant and, against any sort of logic, exhausts herself caring for it, hauling it around, giving up calories and foraging time, making herself more vulnerable to predators with this cumbersome burden. Why toil away with this maternal behavior? Distal explanation: because among primates, high degrees of maternal investment increase the likelihood of survival of the offspring and thus maximization of passing on copies of genes. Proximal explanation: because something about those big eyes and ears with that wrinkly little face and, I can't stand it, that adorable round forehead, and you just have to take care of that kid.

Much of behavior is driven by proximal cues, and never is this more the case than when thinking about the motivation for sexual behavior. For behaviors that are that evolutionarily vital, that so often involve risk to life and limb, the motivation can't be abstract and delayed, like the consequences for genetic competition, or for the promise of offspring after a long gestation period (just imagine how few elephants there would be on earth if elephant sex were motivated purely by the cognitive recognition that, do this and, shazzam, two years later some kid pops out). Sexual behavior has to be driven, overwhelmingly, by proximal cues. Animals, including human beings, are interested in sex because it feels good.

Now that the Gentle Reader is clear about this fact, the question gets more interesting: What proximal cues are the most reinforcing for sex? Basically, what makes one organism sexy to another?

Remarkably enough, scientists have a pretty good sense by now of what qualities give us vertebrates the hots, and there are some consistencies across the animal kingdom. For starters, species from birds to humans seem to like the looks of someone who is average, symmetric in their face and build — the archetype of conventional beauty. People, for instance, can pick up incredibly subtle asymmetries in eyes, ears, wrists, or ankles, and those definitely count against a potential mate.

Why prefer symmetry? The generally accepted explanation is that this signals conventional health (although, as was the point of "Antlers of Clay," you should be cautious about automatically assuming that a case of healthy symmetry is due to genes). This attraction toward averageness accounts for a truly disturbing finding discovered soon after the invention of photography: if you superimpose the pictures of a whole bunch of human faces (or, nowadays, if you generate a computerized average of them), you get this really good-looking imaginary composite android face.

But certain outliers exert an even more magnetic attraction than the averagely healthy. In species after species, the proximal signals generated by females with higher than average appeal are ones indicating atypically high degrees of reproductive potential. Most males in most species respond to whatever their species' equivalent is of a woman with big-time child-bearing hips. And in the numerous species in which males are selected for traits that differentiate them from females, the exaggerated male traits that make hearts throb are those implying successful male-male competition — their equivalent of being buffed up, or possessing a territory or a high rank in a hierarchy. When taken to an extreme, the sexy male in many species is the metabolic equivalent of being economically well-endowed. As reviewed in "Antlers of Clay," this is the strange arena of secondary sexual characteristics among males, the enormous plumage, the wild coloration, the strange appendages. It is a sign of peacock strutting, of conspicuous consumption — "I am so healthy, so parasite-free, so well-off, that I can afford to waste all these calories on something as ridiculous as these huge neon antlers."

So throughout the animal kingdom, individuals of both sexes respond to the conventionally attractive all-American kid next door, but especially respond to the drop-dead gorgeous individual with the amazing ________________ (fill in according to your species and gender). Those are the sorts of traits that provide particularly strong proximal cues toward mating. Now, the demoralizing fact confirmed by Newsweek, the one that all of us run-of-the-mill-looking folks knew all along, is that animals who generate those strong proximal cues get treated better. I don't just mean that good-looking vertebrates get to be more sexually active. They get treated better in all sorts of walks of life.

That's not news, of course, when it comes to humans. Study after study shows that we will listen with rapt attention to someone's raving gibberish, will preferentially give them a job or even vote for them, just because they have gorgeously symmetric wrists. The ones I'm really disappointed by are the nonhuman primates, who are usually more sensible than that.

A study by the ethologists Bernard Wallner and John Dittami of the University of Vienna shows a pretty egregious example of such preferential behavior among Barbary macaque monkeys. When a female comes into heat, she develops a conspicuous anogenital swelling that tells the world of her special ovarian status. Although the size of the swelling increases as a female approaches her ovulation day, some females have bigger swellings than others. And those females get treated better. When compared with females at the same point in their reproductive cycles who have smaller swellings, the well-endowed females are less likely to have males in bad moods displace aggression onto them. Moreover, males are more likely to groom them. Okay, so male macaques get gaga over pneumatic anogenital swellings. The ones who should really know better than that are the females. But they do it too — big-swelling individuals are preferentially groomed by females as well.

This is depressing as hell. Is there a phylogenetically widespread bias to treat individuals by how they look? Is all of evolution from slime molds on up one dazzling trajectory leading to the unlikelihood that Dan Quayle was once vice president? But it turns out that things may not be that bad after all.

A first example of some redeeming sensibility comes from an unlikely source, namely us humans. As discussed in "Antlers of Clay," the psychologist David Buss carried out a celebrated study concerning how people choose their mates, surveying more than ten thousand people from thirty-seven different cultures around the planet. As was noted, in every society studied, women placed a disproportionate emphasis in their mate preference for someone with good economic prospects. In contrast, in society after society, men disproportionately valued youth, someone who possesses the physical features that signal health and fertility.

Fair enough. But what was less reported was a commonality among the women and men of all these different cultures — highest on everyone's list was finding a mate who was kind and who loved them.

Isn't that sweet? Okay, let's be sour cynics for a moment. Buss was surveying what people look for in a mate, not whom they'd like to jump into the sack with right now. Ultimate issues, not proximal ones. Maybe when people are contemplating whom they want to grow old with, a sensible distalness predominates: it makes sense to go for someone who is kind, loving, capable of being a good parent, someone who will remember to put the cap back on the toothpaste. But when we put ourselves back into the realm of proximal cues, it might be that the person who makes your blood run scalding has none of those traits, has bad news written all over them. It seems unlikely that kindness is ever sexy.

Yet the evidence can be surprising.

In recent decades, a revolution has taken place in primatology. It had been thought that sexual behavior among Old World primates (the kinds that live in big social groups, like baboons or macaques) followed a "linear access" model: if a single female was in heat, the highest-ranking male would claim her. And if two females were in heat, males number one and two would mate with them, and so on. The mating patterns were assumed to arise exclusively from the outcome of male-male competition; the females passively wound up with whomever the competition allotted them.

The revolution was the discovery of "female choice," the wildly radical notion that females had some say in the matter. Maybe this had something to do with there having been a transition, such that the best primatologists around were female, and with their looking at the behavior of their animals without that linear-access bias. What was obvious was that some females didn't just passively wind up mating with whichever hunk strutted forward. Being half the size of males in many of these species, females couldn't convince a male they didn't favor to get lost by beating on him.

But they sure could fail to cooperate. Maybe a female wouldn't stand still when the male tried to mate. Maybe, when pursued by a male, she would repeatedly walk right past the male's worst rival, forcing the two into tense interactions. And with any luck, those two male rivals would get so haired out with each other that they would collapse into fighting, giving the female the opportunity to sneak off to the bushes and mate with the guy she is really interested in (a phenomenon called stolen copulations, as well as other, unprintable terms, by primatologists).

But if the female has a choice, who does she choose? Who does attract her to the bushes? The answer, at least among baboons, is stunning: the nice guy. Maybe it is a male with whom she has a "friendship," or a mutual grooming relationship. Maybe he carries her kid to safety when predators are around. Maybe he is the father of that kid. But basically, he is a male who is now favored because of the quality of the relationship he has worked out with her over time — not because he has won some fight with another male.

Let's be clear about what's happening. This is not the case of a female thinking, in effect, Okay, that big hunk over there in the biker jacket is really hot, but be sensible, kiddo, the guy's trouble, better stick with kindly Alan Alda. Just the opposite. These females are manipulating these big, dangerous studs into fighting with each other, are risking life and limb (as they are occasionally subject to fatal displacement aggression at the teeth of those frustrated males), all to sneak off to the bushes to have sex with the Alan Aldas of their society. Think about it: nice can be proximally sexy.

This is extraordinary. And even more extraordinary, genetic studies of paternity have shown that in some species, male primates who bypass overt male-male competition and instead covertly copulate in the bushes do pretty well for themselves in the task of passing on copies of their genes. By the coldly calculating bottom line of evolution, this niceness business is not just some foolish sentimentality; it's a successful strategy.

So let your average, callow primate get all crazed and libidinous over how someone looks or smells. For the monkey who actually cares about how he treats someone, the evolutionary payoff is at least as great. This is pleasing news on a proximal level: even for a nonhuman primate, the most erogenous organ can be the mind. Or the heart. And this is pleasing news on an ultimate level as well, for all of us who have been tempted to jettison our kindergarten lessons about being nice and sharing in favor of sad adult jadedness about looking out for number one. Maybe that notoriously asymmetric sage Leo Durocher was wrong with that business about nice guys finishing last.

Copyright © 2005 by Robert M. Sapolsky