Sex, Murder, and the Meaning of Life (13 page)

So the parsimony of domain-general theories comes at a price. They are often too lean on the devilish details that make for complete explanations. When I said earlier that the human brain uses different sets of rules for making decisions about the different people in our lives, I was instead advocating a
domain-specific
theory. In this view, there is no unitary “self” inside your head. Instead, there is a confederation of modular subselves, each one specialized to do one thing well.

Some of the best evidence for domain-specificity comes from research on animal learning, the same body of research that spawned reinforcement-affect theory. Running contrary to the vogue for
simple models during the 1960s, several behavioral psychologists began to uncover evidence that the rules of conditioning seemed to change depending on what was being learned and which species was doing the learning. Consider the rules involved in learning to avoid poisonous foods. A fundamental behaviorist principle was that conditioning works best when there is instantaneous feedback. For example, if you receive a jolt of pain immediately after touching a hot frying pan, that teaches you not to touch a smoldering frying pan again; the pain does not get associated with the washcloth you used to wipe the pan out five minutes earlier. But research on conditioned nausea showed that the principle is sometimes violated. For example, one night I was hit with a dreadful bout of nausea at four in the morning. I did not associate the nausea with my bathroom or even with the Alka-Seltzer I had taken minutes before I became sick. Instead, I associated my upset stomach with a shrimp dish I had eaten at a party several hours before becoming ill (wrongly so, it turns out, because I was actually coming down with a flu). In this case, my mental mistake was based on a special exception to the rules of conditioning, an exception also found in other omnivorous animals. John Garcia and Robert Koelling found that rats learn to avoid foods that made them sick many hours after the food was eaten. Garcia and Koelling also found that food aversions are unlike many other types of learning in other ways: Food aversions require only one trial to learn and are very difficult to extinguish. In my case, for example, the powerful automatic aversion to possible toxins has totally overridden my conscious understanding that it was the flu and not the shrimp that was to blame—I still feel sick just thinking about those innocent little crustaceans. Garcia and Koelling's findings were revolutionary, suggesting that different forms of learning reflect different adaptive features. By conditioning strong aversions to any novel foods eaten several hours before, an omnivorous animal is better able to avoid toxic substances whose effects might not show up immediately. Like
many novel ideas, though, Garcia and Koelling's findings were initially rejected by other scientists.

There is another functional twist to the research on food aversion: It is not just any cues that get conditioned to nausea. Instead, an animal's particular evolutionary history determines which associations that animal learns. For example, rats, which have poor vision and rely on taste and smell to find food at night, easily develop aversions to food that tastes unusual but not to food that looks unusual. Another team of researchers demonstrated quite a different pattern of learning for quail. These birds search for food relying not on taste but on their keen visual sense, and so quail condition nausea more easily to the color of a new food than to its taste.

So instead of having brains that operate on one or two domain-general rules, animals have subdivided minds. This revolutionary insight does not apply only to food aversions. David Sherry and Daniel Schacter reviewed numerous findings to show that there are several different kinds of memory, even in a bird's seemingly simple little brain. The rules governing how a bird remembers to tweet its species song are completely different from the rules that govern how it remembers where it stashed the winter supply of nuts, and both these memory systems are completely different from the memory systems that govern how it learns which foods are nutritious and which make it sick. Most importantly, the nature of the divisions inside any animal's head depends on the animal in question. Bats, for example, have a whole set of special mechanisms in their brains designed to allow them to paint a sonogram of the night sky. Their earthbound mammalian cousins, like us, do not.

It was fashionable for much of the twentieth century to argue that as the human brain grew larger, it lost most of its biological constraints.
But like tie-dyed bell-bottom trousers and smoking fat cigars in California restaurants, that argument has now gone out of fashion. For one thing, we humans, like rats, have different systems for remembering food aversions as opposed to food preferences. Our brains also have different systems for perceiving the sound of a sparrow singing and the color of its wings, and those systems are themselves subdivided (for example, the mechanisms for processing color involve different groups of neurons from those involved in processing shape and still different systems from those used to process movement). Likewise, our brains use one system for understanding the words we hear and another one for producing the words that come out of our own mouths.

Some of these different mental systems are geographically segregated, but some are not; many of them share some subprograms; and virtually all of them require appropriate developmental inputs to fully unfold (think of the simple two-word sentences coming out of a two-year-old's mouth and the complex things the same child can say two years later). Furthermore, there is enough neural plasticity that people who suffer brain damage can recover some of their lost abilities. But to say that the brain has some flexibility and that the brain's development involves continual interaction with the environment should not be taken to say that our heads contain blank slates full of interchangeable multipurpose neurons. Instead, our brains come with abundant preprogramming, which develops into a number of special suborgans during normal development.

How many subdivisions does the normal human brain have? We are still learning the answer to that question. But we now know that “one” was the wrong answer. Many evolutionary psychologists advocate what is called the “massive modularity” position. On that view, our heads are chock-full of independently operating little machines, each solving one particular problem. Researchers who have studied human emotions and animal instincts like to paint with a broader
brush and think about organized systems of adaptive mechanisms. I think the two perspectives need not be mutually exclusive—that is, both may be true, depending on how you slice it.

I will return later to the question of how to subdivide the human brain after I talk about two relevant sets of research studies. One looks at some intriguing similarities in the sexual preferences of homosexual and heterosexual men. The other looks at the different reactions people have to sharing credit versus sharing sex with kin, friends, and strangers.

When I was nineteen years old, the sexual revolution was raging. In New York City, where I grew up, there were love-ins in Central Park, and beautiful young women walked around in loose halter tops without bras, apparently proud of their newly liberated sexuality. One night I took the subway into Greenwich Village, dressed in my finest bell-bottoms and a peacoat, with the brilliant idea that I would hang out on the street until one of these sexually free beauties started flirting with me. I stood around awkwardly for a while, not getting much eye contact from the members of my target audience. Just when I was about to give up my plan, however, I heard the classic pick-up line: “Don't I know you?” However, it was not a braless young hippie woman with flowing blonde hair who was approaching me but, rather, a middle-aged black man in a conservative suit.

It turned out that I actually had briefly met this fellow earlier, so I did not know what to think when he seemed surprised by my “yes” answer. After a brief conversation, I realized that his question had only been a pick-up line and that he had forgotten an earlier conversation we had had when he came by the hotel where I worked as a doorman. I did, though, have a pleasant and illuminating conversation with the fellow, who had studied psychology in graduate school.
When I told him about my evening's plan to meet a woman, he wisely informed me that standing by myself on a street in Greenwich Village was more likely to result in meeting a homosexual man out for a one-night stand. I also had a brief chat with him about a troubling experience in which a man renting a room from my old girlfriend had made an aggressive pass at me, and I confessed that I was beginning to wonder if my attempt to act like a hip urban intellectual type wasn't somehow sending off incorrect signals about my sexual orientation. He reassured me that this was not the case, but he told me that homosexual guys were, like heterosexual guys, more proactive than women when it came to searching for new mating opportunities. Although neither of our sexual fantasies were fulfilled that evening, I did board the subway home with a slightly better understanding of the commonalities between heterosexual and homosexual men, as well as an unanswered question about why older homosexual men are interested in meeting guys so much younger than themselves.

A few years later, I actually did some research to help answer that question. As I discussed earlier, Rich Keefe and I had found that throughout their lives, except during adolescence, heterosexual men are interested in younger women, and that this desire seems to be all about fertility cues. And as I also discussed, women pursue older men because age in a man carries implications of status, wealth, and other advantages. An interesting question—and one that has direct bearing on our discussion of the modularity of the mind—is, What kind of men are
homosexual
men attracted to? As it turns out, homosexual men share with heterosexual men not only a tendency to be more proactive in seeking partners but also a host of other similarities. On the other hand, the guys homosexual men desire are surprisingly unlike those desired by heterosexual women. For example, Michael Bailey and his colleagues found that, like heterosexual men, homosexual men want a good-looking partner and do not care much about whether the guy is wealthy or high status. And when Keefe and I did
a study of age preferences in homosexuals, we found that older gay men are, like older heterosexual men, attracted to much younger partners. This poses something of a problem for older homosexual men. Although an older heterosexual man stands a chance of finding a younger woman who reciprocates his interest, younger gay guys are not attracted to older men. Instead, like the older men, young homosexual men are interested in young men too.

The whole pattern is puzzling in several ways. Homosexual men's attraction toward younger attractive partners is not the result of reinforcement patterns (younger gay men do not reward an older guy's interest); it is not the result of adopting societal values about what is attractive in a man (or else gay guys and straight women would want the same thing); it is not the result of conscious rational decision-making (older homosexual men without permanent relationships often complain bitterly of loneliness, which could be alleviated by pairing up with another lonely older gay guy).

Homosexuals' general preference for members of their own sex still presents something of a puzzle from an evolutionary perspective, but homosexual men's preferences for young attractive partners are less puzzling. In fact, those preferences help shed additional light on the extent to which the brain is modular. The many similarities between gay men and heterosexual men suggest that human mating behavior, like human vision, is not simply a one-switch mechanism. Although the switch for sexual orientation has a different setting in homosexual and heterosexual men, for whatever reason, homosexual men's full pattern of preferences indicates that most of the other switches are still set at the same default settings as those of heterosexual men—generally speaking, both want young attractive partners, both want a lot of partners, and neither cares about the wealth or status of their partners. In most ways, other than the direction of their preferences, homosexual men are playing out a mating strategy that would otherwise result in high reproductive success (if their targets were women).

On our European vacation from hell, I tolerated a lot more annoyance from my son Dave than I did from my lifelong friend Rich. Indeed, the way people feel about their friends as opposed to their relatives also offers some interesting insights into our minds' modularity. In some ways, friends and relatives share a similar place in our hearts, both typically triggering a lot of positive associations. My former student Josh Ackerman and I conducted an experiment in which we asked subjects to play a team quiz game, either with a parent, a sibling, a friend, or a stranger. All the teams were told they had done exceptionally well, regardless of their actual performance. When we asked them who was responsible for their team's success, people playing with strangers took the lion's share of the credit. People who played the game with relatives gave more credit to those family members. Friends were generally given more credit than strangers, although there was an unexpected split along sex lines. Women shared credit with their friends as though they were kin, but men treated friends a bit more like strangers.

Working with Mark Schaller, Josh and I did another study that moved into a rather taboo area at the borderline between friendship and kinship. We asked college students to concentrate on what it would be like to have sex with a stranger, a friend, or a close relative. It may surprise you to know that we are not the only researchers who have asked people to imagine having sex with relatives. In fact, consistent with their inclination to have one foot in the gutter, several evolutionary psychologists—including anthropologist Dan Fessler and psychologist Deb Lieberman—have done similar work, and we have all found similar results. People, both men and women, generally find the very thought of sibling sex quite disgusting. On the other hand, when thinking about sex with strangers—people who are not usually the targets of positive associations—our subjects
experienced almost no disgust and more positive than negative feelings.