Homo Mysterious: Evolutionary Puzzles of Human Nature (46 page)

Group size is essentially a proxy for social complexity; as group size increases, the number of possible interactions increases geometrically. So if intelligence evolved because of the payoff it provides in solving social problems, there should be a positive correlation between group size and brain size. There is. Dunbar has shown that neocortex size varies directly with group size in many mammals.
²¹
Small-brained monkeys tend to have simple social structures, baboons experience more complex social groupings and have larger brains, and chimps more so yet. And human beings? The most, and the largest. Dunbar also suggested that physical grooming, as found among nearly all nonhuman primates, eventually gave rise to language among human beings, since both
activities serve to modulate interactions among individuals. As Dunbar sees it, when early human social groupings became too large for ancestral humans to keep track of each other via direct physical contact, evolution favored the ability to maintain “contact” verbally, via language, and with it, dramatically increased intelligence and brain size.

An interesting hypothesis, but once again, it’s not quite a “slam dunk.” For one thing, social insects, for example, have complex social relationships but very simple brains and a “language” that is chemical rather than verbal. In addition, who is to say that the correlation didn’t proceed in the other direction, with higher intelligence having evolved for some other reason or reasons, itself making social relationships more complex? This could be because as individuals became smarter, their interactions would likely have become more sophisticated and elaborate, conferring yet more benefit upon those who were smart enough to navigate these complexities effectively. If so, then instead of social complexity being a cause of intelligence, it might have arisen largely as a result.

Just as most biologists agree that the generation of diversity is quite likely the major adaptive significance of sex, maybe the adaptive value of intelligence is that it allows us to cope with diversity and complexity in general, whether environmental or social. If so, it is also paradoxically the case that intelligence itself may generate diversity—at least, diversity within social settings—which in turn creates an interpersonal environment that favors yet more intelligence.

The boundaries may well be porous and indistinct between selection for intelligence as a result of social pressures and selection for intelligence as a means of prospering in a given ecological niche. If our ancestors grew smart as a consequence of selection for ability to master difficult habitats, there is no reason to doubt that evolution could eventually have transferred mastery over the environment to mastery over other individuals in the same group and, via primitive warfare and intergroup competition, between different groups as well. In a similar process, it is widely agreed that certain dinosaurs initially evolved feathers as an aid to thermoregulation, after which selection acted on these devices to achieve a new payoff: flight, and a new group of animals, called birds. Maybe our own soaring intellects and flights of imagination
were similarly achieved, having evolved initially in response to one kind of payoff (involving ecological challenges) and then later transferred into another (involving social challenges).

There is a common thread connecting the above “social intelligence” hypotheses, namely, the supposition that aside from potentially direct survival benefits vis-à-vis obtaining food, avoiding predators, and competing mano-á-mano with other proto-human groups, we evolved our intellects at least in part in the context of living complex and demanding social lives. And this approach, in turn, fits with an important emerging concept: that our brains have not evolved as all-purpose, generic, logical problem solvers. Rather, human mental functioning is increasingly seen by evolutionary psychologists as divided into a toolkit of diverse and distinct mental modalities, each adapted to solve a particular kind of survival-and-reproduction challenge.

Even among psychologists whose orientation is distinctly nonevolutionary,
^iv
there has long been serious debate about whether anything like generalized intelligence exists at all. Beyond the discussion of such things as “emotional intelligence” and the distinction between performance IQ and components of intelligence associated with verbal or mathematical capabilities, the perspective of evolutionary psychologists in particular is that human intelligence is essentially divided into various “domain-specific” modes. John Tooby and Leda Cosmides have been especially vigorous in promoting this approach, with a series of studies demonstrating that people are endowed with intelligence designed to detect cheaters in situations of social exchange, as opposed to conditions of pure logic.
²²

We have already noted that the human mind did not develop as a calculator designed to solve logical problems. Rather, it evolved for a very limited purpose, one that is ultimately no different from
that of the heart, lungs, or kidneys; that is, the job of the brain is simply to enhance the reproductive success of the body within which it resides (and in the process, to promote the success of the genes that produced the body, brain and all).

This is the biological purpose of every mind, human as well as animal, and moreover, it is its
only
purpose. The purpose of the heart is to pump blood, the lungs exchange oxygen and carbon dioxide, and the kidneys work to eliminate toxic chemicals. The brain’s purpose is to direct our internal organs and our external behavior in a way that maximizes our evolutionary success. That’s it. Given this, it is remarkable that the human mind is good at solving any problems whatsoever, beyond “Who should I mate with?” “What is that guy up to?” “How can I help my kid?” and “Where are the antelopes hanging out at this time of year?” There is nothing in the biological specifications for brain building that calls for a device capable of high-powered logical reasoning, or solving abstract problems, or even providing an accurate picture of the “outside” world, beyond what is needed to enable its possessors to thrive and reproduce.

Here is a particularly revealing example, known as the Wason Test. Most people’s performance on this simple test reveals a pronounced inability to solve a simple logical problem, combined with remarkable cleverness when the same situation is reframed as a variant in one’s socio-Machiavellian intelligence.

Imagine that you are confronted with four cards. Each has a letter of the alphabet on one side and a number on the other. You are also told this rule: If there is a vowel on one side, there must be an even number on the other. Your job is to determine which (if any) of the cards must be turned over to determine whether the rule is being followed. However, you must only turn over those cards that
require
being turned. Let’s say that the four cards are as follows:

S 4 A 7

Which ones should you turn over? (Remember, you want to assess this rule: If there is a vowel on one side, there must be an even number on the other.)

Most people realize that they don’t have to inspect the other side of card “S.” However, a large proportion respond that the “4” should be inspected. They are wrong: The rule says that if one
side is a vowel, the other must be an even number, but nothing about whether an even number must be accompanied by a vowel. (The side opposite a “4” could be a vowel or a consonant; either way, the rule is not violated.) Most people also agree that the “A” must be turned over, since if the other side is not an even number, the rule would be violated. But many people do not realize that the “7” must also be inspected: if its flipside is a vowel, then the rule is violated. So, the correct answer to the above Wason Test is that “S” and “4” should not be turned over, but “A” and “7” should be. Don’t feel badly if you had trouble with this; fewer than 20% of respondents get it right.

Next, consider this puzzle. You are a bartender at a nightclub where the legal drinking age is 21. Your job is to make sure that this rule is followed: People younger than 21 must not be drinking alcohol. Toward that end, you can ask individuals their age, or check what they are drinking, but you are required not to be any more intrusive than is absolutely necessary. You are confronted with four different situations, as shown below. In which case (if any) should you ask a patron his or her age or find out what beverage is being consumed?

Nearly everyone finds this problem easy. You needn’t check the age of person #1, the juice drinker. Similarly, there is no reason to examine the beverage of person #2, who is older than 21. But obviously, you had better check the age of person #3, who is drinking beer, just as you need to check the beverage of person #4, who is underage. The point is that this problem set—which is nearly always answered correctly—is logically identical to the earlier set, the one that causes considerable head scratching, not to mention incorrect answers.

Why are the second problems so easy, and the first so difficult? Cosmides and Tooby, who have extensively researched different variants on these two problems, conclude that the key isn’t logic itself—after all, they are logically identical—but how they are positioned in a world of sociobiological reality. Thus, whereas the first is a matter of pure logic, disconnected from the real world, the second plays into issues of truth telling and the detection of
social cheaters. The human mind, Cosmides and Tooby point out, is not adapted to solve rarified problems of logic, but is quite refined and powerful when it comes to dealing with matters of cheating and deception.
²³

The card example just described is a special case of the more general phenomenon, known as a “conditional rule.” Such rules are simple statements, familiar to logicians: “If P then Q.” The rule is violated if, in a given situation, P is true and at the same time, Q is false. There are lots of ways of stating such conditional rules, all of which are more or less familiar: for example, “If someone lives in Miami, he or she experiences warm weather”; “If someone loves chocolates, then he or she will buy some on the way home”; “If someone is skiing, then it is winter.” It turns out that only about 25% of subjects do a good job of detecting violations of such rules. On the other hand, if the rule is something like this—“If you attend a movie, you must buy a ticket”—then people are much better at detecting violations: About 75% get it right!

Once again, people tend to perform poorly at the Wason task, except when it is presented in terms of possible rule violation—not violations of rules of logic, but of rules governing social exchange. The take-home message here seems to be that when it comes to the evolution of our “higher mental faculties,” an important driving force has involved protecting a potential cooperator from being exploited by someone who takes without giving (thus violating the expectations of reciprocity) or who simply doesn’t play by the rules of social exchange.

Those rules are important, and not simply when it comes to good manners. Indeed, good manners themselves are important precisely because they indicate that someone can be trusted. Second only to interactions among family members (kin selection), it appears that being a reliable reciprocator is the cornerstone of social life. As Yogi Berra reputedly summed it up (sort of): “Always go to other people’s funerals, or else they won’t come to yours.”

As yet, no one can say exactly how important the “social brain” and Machiavellian intelligence have been, and how they stack up
against the various other drivers of human intelligence. Ironically, a problem with these hypotheses is that they are, if anything, too plausible. If human intelligence skyrocketed because our ancestors lived in social groups surrounded by other, comparable individuals, each with his or her agenda, and which in turn drove the evolution of elaborate mental capacities so as to maneuver effectively in such fraught interpersonal traffic, why didn’t the same thing happen to other species? Wild horses and wildebeest live in large social groups: Why haven’t they evolved minds as sapient as ours along with fancy brains to undergird them? And what about ants?

Here’s a possible answer: Maybe the driving forces behind human intelligence were multifactorial, a perfect storm of several different adaptive pressures and opportunities, no one of which would have been sufficient in itself but which, combined, produced those intellects we so proudly identify as quintessentially ours. Maybe being essentially weak bodied turned out to be a paradoxical asset, inducing our more intelligent forebears to be favored over the duller ones. Maybe the elaboration of language, combined with discovery of tools, added to rapidly changing environments, along with vigorous competition (potentially warlike as well as more subtle, within-group), plus sexually selected preferences … all added up to a unique and intelligence-favoring configuration of circumstances that simply didn’t arise for other species.
^v