Human. Part 2

INTO THE TROPICAL FORESTS.

Until January 7, 1974, scientists treated the remarkable violence of humanity as something uniquely ours. Then in Gombe National Park, Tanzania, Hillali Matama, the senior field a.s.sistant from Jane Goodall's research center in Gombe, observed for the first time a raiding party of chimps furtively entering the territory of another chimp group and killing a lone male who was quietly eating, and the subsequent systematic killing of the rest of the males in that rival group over the next three years. And the females? Two of the young females transferred into the raiding group, one watched her mother beaten to death by her new group, and four others disappeared. What was more shocking was that these groups had originally all been one community. More observations were recorded from other areas and observers. Toshisada Nishida's team in Tanzania's Mahale Mountains National Park (the only twenty-year chimp research program other than Goodall's) has seen violent charges toward strangers by border patrols and furious clashes between male parties from neighboring communities.

Since these first observations, two entire chimpanzee communities have been exterminated by their own kind. Other observers of nonhuman primates witnessed male gorillas and some monkey species killing infants, and male chimpanzees and orangutans raping females. As more field observations were recorded, we've learned that although infanticide is typical behavior in many species within every group of animals-birds, fish, insects, rodents, and primates, practiced by males, females, and infants, depending upon the species-killing adults is not.

Richard Wrangham, professor of biological anthropology at Harvard, believes we can trace the origins of human violence, particularly male violence, to our origins as apes, and more specifically to our common ancestry with the chimp. In his book Demonic Males, he has a convincing argument. 64 He states that the most compelling set of facts that point to this conclusion is involved with the similarities of our two societies. "Very few animals live in patrilineal, male-bonded communities wherein females routinely reduce the risks of inbreeding by moving to neighboring groups to mate. And only two animal species are known to do so with a system of intense, male-initiated territorial aggression, including lethal raiding into neighboring communities in search of vulnerable enemies to attack and kill. Out of four thousand mammals and ten million or more other animal species, this suite of behaviors is known only among chimpanzees and humans."*

Wrangham reports that observational studies have found chimps to be patriarchal. Males are dominant, inherit territory, raid and kill their neighbors, and gain the spoils (not only increased foraging, but neighboring females), but they also are killed if they lose their territory. Females, however, gain a different advantage. They can remain in their territory and continue to forage by simply changing allegiance to the conquering band. They remain alive to reproduce again, whereas the male is killed. OK, so chimps are patrilineal, but what about humans?

Wrangham reviews the ethnographic records, studies of modern-day primitive peoples, and archaeological finds to show that humans are, and always have been, a patrilineal society, regardless of what some feminist organizations a.s.sert. (It is interesting to note that while I type this in my Microsoft Word program, the word patrilineal is underlined by the spell-check feature as having been spelled incorrectly, and the suggested spelling is for the word matrilineal, which is never underlined as having been spelled incorrectly.) It has been argued that this patriarchy is a cultural invention, but a new field of study, branded evolutionary feminism, views patriarchy as a part of human biology.

And lethal raiding? Wrangham postulates that there is the possibility that intergroup aggression has a common origin because it is unusual among other animals. Although human aggression is well known in the modern world, he also sees patterns of violence in current primitive cultures that are similar to the chimps' violence. One example is the Yanomami, an isolated cultural group of twenty thousand people living in the lowland forests of the Amazon basin, who are famous for intense warfare. They are subsistence farmers having plenty of food, and each community is made up of about ninety members. Men stay in the village of their birth, and the women change communities at marriage. The Yanomami do not fight over resources but most often over women. Thirty percent of Yanomami men die from violence. However, the violent raiders are rewarded. They are honored by their society and have two and a half times the number of wives as other men and three times the number of children. "Lethal raiding among the Yanomamos gives the raiders genetic success.

"The conditions that make Yanomami society similar to that of chimps are their political independence and the fact that they have few material goods and no gold, valuable objects, or stores of food to fight over. In this stark world, some of the more familiar patterns of human warfare disappear. There are no pitched battles, no military alliances, no strategies focused on a prize, and no seizure of stored goods. What remain are the penetrating expeditions in search of a chance to attack, to kill a neighbor, and then to escape."* Thirty percent of male chimps die from aggression in Gombe National Park, the same percentage found in the Yanomami villages. Mortality rates from aggression in other primitive tribes are similar: in highland New Guinea, Australia, and the !Kung of the Kalahari. As Wrangham observes, hunter-gatherer societies don't fare any better under the microscope.

A handful of societies have managed to avoid outright war for extended periods. Switzerland is the best modern example. However, to retain their peace, as John McPhee writes in La Place de la Concorde Suisse, "There is scarcely a scene in Switzerland that is not ready to erupt in fire to repel an invasive war." The Swiss maintain the largest army per capita in the world, enforce compulsory military service, bury live mines at critical bridges and pa.s.ses, and keep deep caves carved into mountains stocked with enough medical supplies, food, water, and equipment to last the full army and some civilians a year or more. They also are isolated by the Alps.65 So, humans and chimps are patrilineal, and both humans and chimps have a history of lethal raiding. And it is well known that human males are more violent than females. Violent crime statistics from around the world reflect that. So agreeing on our similarities, let's hear why Wrangham thinks this happened. It boils down to the ecological version of economics; something called cost-of-grouping theory, which basically states that the size of the group depends on its resources. In an environment where food is seasonal or erratic, the party size will vary accordingly: more food, bigger parties; less food, smaller parties. Whether a group has to travel, or how far it has to travel, depends on what they eat. Some species have a food source that is abundant and stable, so their groups end up being stable (such as gorillas, who sit around and eat leaves all day). However, some species have evolved to eat high-quality, difficult-to-find foods that aren't always available, such as nuts, fruits, roots, and meat. Here we are like the chimps.

Bon.o.bos, on the other hand, are different. They eat what the chimps eat but also the abundant leaves that gorillas eat, without the gorillas to compete with. They don't have to travel far to find food; they live on Easy Street. The type of food that we and the chimps eat has made males more dominant. Traveling to find food slows down the females, who carry and nurse the infants. The guys and the childless females can go farther and faster and get to the patch of food first, and then hang out together. They can afford to have larger parties. The advantage of moving around to find food with a variable party size gives a species flexibility and the ability to adapt to changing environments, but the disadvantage is that when the group becomes small, it is vulnerable to attack from a temporarily larger group. This is what Wrangham calls a party-gang species: species with coalitionary bonds (the males hanging out together) and variable party size.

What makes it possible for these species to kill, just as it is possible for some species to indulge in infanticide, is once again economic. It is cheap to kill. The cost-to-benefit ratio is good. When you kill an infant, you don't really risk being injured yourself, so the cost is low. You gain either a food source or increased chance of mating with the female, because when her infant is dead, she will stop lactating and ovulate again. When you are in a gang against a weaker neighbor, once again the risk of injury is low. What do you gain? It weakens the neighbors, which is always good for the future, expands the food supply, and finds you mating once again.

But why are the males so aggressive? Has s.e.xual selection selected for male aggression? Although they do not have large canine teeth, all apes can fight with their fists. Adapted for swinging in trees, the shoulder joint can rotate, and an ape's long arms and a balled-up fist can pack a punch that keeps opponents at bay. Fists can also grasp weapons. Chimps are known to throw rocks and branches. At p.u.b.erty, both ape and human males develop increased upper body musculature and broad shoulders as the shoulder cartilage and muscle respond to increasing testosterone levels. But even though there is a physical ability to be aggressive, not all strong animals are.

What is going on in the brain department? We can grasp the idea that animals can't control their emotions or urges, but aren't humans able to control their aggression through cool reasoning? Well, it turns out that it isn't as simple as that. Antonio Damasio, head of the neurology department at the University of Southern California, has studied a group of patients who have all had damage to a particular location of the ventromedial part of the prefrontal cortex.* They all lack initiative, can't make a decision, and are unemotional. One patient whom he studied closely tested normally in intellectual ability, social sensitivity, and moral sense, and could devise appropriate solutions and foresee consequences to hypothetical problems, but he could never make a decision. Damasio concluded that this patient and other similar ones could not decide because they were unable to connect an emotional value to an option: Pure reason was not enough to make a decision. Reason made the list of options, but emotion made the choice.66 We are going to talk about this in later chapters. What is important to know now is that even though we humans like to think of ourselves as being able to make non-emotional decisions, emotions play a part in all decisions.

Wrangham concludes that if emotion is the ultimate arbitrator of an action, the emotion that underlies aggression for both chimps and man is pride. He states that male chimps in their prime organize their whole lives around their rank. All decisions are guided by it, including when they get up in the morning, with whom they travel, whom they groom, and with whom they share food. All actions have the goal of becoming the alpha male. The difficulty of reaching this position causes aggression. With humans it is much the same. Wrangham quotes Samuel Johnson, who observed in the eighteenth century, "No two people can be half an hour together, but one shall acquire an evident superiority over the other." Just as today, men flaunt their status with expensive watches, cars, houses, women, and cla.s.s-conscious societies.

Wrangham hypothesizes that pride "evolved during countless generations in which males who achieved high status were able to turn their social success into extra reproduction."* It is a legacy of s.e.xual selection. Matt Ridley concludes his chapter about the nature of women in his book The Red Queen, "There has been no genetic change since we were hunter-gatherers, but deep in the mind of the modern man is a simple male hunter-gatherer rule: Strive to acquire power and use it to lure women who will bear heirs; strive to acquire wealth and use it to buy other men's wives who will bear b.a.s.t.a.r.ds. It began with a man who shared a piece of prized fish or honey with an attractive neighbor's wife in exchange for a brief affair and continues with a pop star ushering a model into his Mercedes."67 So men and chimps are physically prepared for physical aggression and emotionally primed to achieve high status, but so are solitary orangutans, while humans and chimps are social. Pride accounts for social aggression also. Any group-whether it is a team, a religion, a s.e.x, a business, or a country-can have a devoted following, but why? Is it the result of rational deliberation, or is it an innate response of an old ape brain?

Social psychologists have shown that group loyalty and hostility emerge with predictable ease. The process begins with groups' categorizing into Us and Them. It is called the in-groupout-group bias and is universal and ineradicable: French-speaking Canadians versus English-speaking Canadians, police versus FBI, Broncos fans versus everyone else, Stones fans versus Beatles fans.... This is to be expected in a species with a long history of intergroup aggression. Darwin wrote, "A tribe including many members who, from possessing in a high degree the spirit of patriotism, fidelity, obedience, courage and sympathy, were always ready to aid one another, and to sacrifice themselves for the common good, would be victorious over most other tribes, and this would be natural selection."* He wrote this to show how morality could emerge out of natural selection for solidarity. Wrangham also suggests that morality based on intragroup loyalty worked, in evolutionary history, because it made groups more effectively aggressive.

CONCLUSION.

Sometimes looking at the family tree isn't always pretty, but it can explain many seemingly mysterious behaviors. Many a couple has come to grief because they ignored their prospective partner's family. In the case of our chimp date, we have a common ancestor; the families have diverged in many respects but still share many characteristics, as Richard Wrangham has pointed out. We have seen how the anatomy of our body has changed significantly and been the basis for changes that have led to many of our unique features. Bipedalism led to free hands and changed breathing patterns. Our arching and opposable thumbs have made it possible for us to develop the finest motor coordination of any species. Our unique larynx has allowed us to make the infinite number of sounds that we use for speech. Our mirror neuron system is far more extensive than has been found in other species, and we will see that it has far more ramifications than just language. Other changes have been going on in our brains, changes that allow us to understand to a far greater extent than our chimp relatives that others have thoughts, beliefs, and desires. Building on these differences, we will move to the next chapter and see where it takes us. I think a day spent with Kanzi would be very interesting, but for the long term, I prefer more culture. Make my date a h.o.m.o sapiens.

Part 2.

NAVIGATING THE SOCIAL WORLD.

Chapter 3.

BIG BRAINS AND EXPANDING SOCIAL RELATIONSHIPS.

It is good to rub and polish our brain against that of others.

-Michel de Montaigne.

IMAGINE: YOUR STOIC DAUGHTER COMPLAINS OF ACUTE ABDOMINAL pain while you are on vacation. You know that if she is complaining, then it is serious. You arrive at the ER with your wife and daughter, and the surgeon on duty, a total stranger, after a two-minute examination, says an emergency appendectomy is in order, now. You remember that a high-school buddy is a doctor in town, miraculously reach him on the phone, and get the rea.s.surance that your daughter is in good hands. Everything is a go, and the surgeon is let into your new alliance. Old alliances are reestablished, new alliances are formed, and there is a successful surgery-followed by breaking of these fresh, fleeting alliances. The social mind is at work.

Imagine: You have signed on to take a guided trip to a rather adventurous locale, a place you would not attempt on your own. You are meeting with your group and guide the first morning. Glancing around at unfamiliar faces, you wonder, What was I thinking? However, two days later, you are clambering up a narrow winding path, trusting a person you have known for only forty-eight hours. Later you are having an interesting lunch conversation with a nearly complete stranger, and that evening you are asked to join a small group for dinner. By the end of the week, the tour group you are in has divided itself into subgroups, which in turn have subgroups. The coalitions shift by the minute. The social mind is abuzz with ties being made and broken and, among other things, the phenomenon of human politics is apparent.

Forming and reforming social groups and alliances are what we do all the time. This is the big picture. And yet many experimental scientists like me have focused on pieces of the big picture. We have been struggling to grasp what may well be inherent fundamental cognitive skills that enable us to form categories, deal with quant.i.ty, or a.s.semble piecemeal sensory input into wholly perceived sensations. We have not focused on what the human brain does best, what it seems built to do: think socially.

It is all about social process. Although we are highly skilled at categorizing people, animals, and things, we don't think about triangles and squares and red and blue. I don't look at the person walking down the street with a dog and think, "Well the head is a circle, the torso a triangle, and whoa, lookee there, four rectangular extremities, well, I guess I should say cylindrical, and then, well, we've got those ten cylindrical fingers...now for the dog." The fact is, we evolved with lots of other humans around, and developed brain capacity to monitor social behavior in large groups so that we may a.s.sess the value of cooperation, the risk of noncooperation, and so on. When one wakes up to this fact, that we are a bunch of party animals, not solitary hermits or mere perceptual data evaluators, suddenly a new question presents itself. If we are so social, how did that happen? Where did that come from? Were our ancestors social? How can natural selection result in group cooperation? Does natural selection work only to select for individual cognitive traits? Or does it work to select for group behavior as well?

This core issue grabbed the attention of Charles Darwin. While he pushed the view of the survival of the fittest, he was well aware of the seemingly paradoxical fact that many creatures make themselves less fit so the group may survive. In the worlds of bees and birds, this goes on all the time, and these phenomena have given rise to the view that natural selection must work on whole groups. Indeed, such mechanisms could well serve as the cornerstone for the emergence of human social and ethical behavior.

That was all fine until the great evolutionary biologist George Williams put the idea of group selection to rest (for a while). In an interview, he recounted his insight that "natural selection works most effectively at the individual level, and adaptations that are produced are adaptive for those individuals, in compet.i.tion with other individuals of the same population, rather than for any collective well-being."1 Natural selection is not the mechanism at work on social processes and norms, which come into and out of existence so quickly. Individual selection also means that living organisms are not adapted to prevent the extinction of their own species. Organisms would be wily at preventing only their own personal extinction. Williams's "adaptationist" paradigm has dominated thinking in evolutionary biology for the past forty years.

Armed with Williams's a.n.a.lysis, Richard Dawkins, the evolutionary biologist who holds the Charles Simonyi Chair for the Public Understanding of Science at Oxford University, took it further and became the vanguard for the idea of the selfish gene. On reading the idea that natural selection works only on genes, one might argue that altruism and all other ideas that favor groups were incidental. It is easy to imagine that this sort of thinking was loathed by many, including the well-known paleontologist and evolutionary biologist Stephen J. Gould, who referred to the core belief that natural selection works only on genes as "Darwinian fundamentalism."

Dawkins had also built on the work done by William Hamilton in the early 1960s at the London School of Economics and the University College London, who had established a Darwinian view for altruism. Hamilton worked on kin selection, and was able to show by a simple mathematical formula (C < r="" b,="" where="" c="" is="" the="" cost="" to="" the="" actor,="" r="" is="" the="" genetic="" relatedness="" between="" the="" actor="" and="" the="" recipient,="" and="" b="" is="" the="" benefit="" to="" the="" recipient)="" that="" our="" human="" preference="" for="" altruism="" has="" a="" rationale="" using="" models="" of="" shared="" genes.2="" this="" implied="" a="" limited="" restraint="" on="" selfish="" compet.i.tive="" behavior="" and="" the="" possibility="" of="" limited="" self-sacrifices.="" if="" you="" were="" closely="" enough="" related,="" it="" would="" make="" genetic="" sense="" to="" help="" out="" a="" relative.="" he="" went="" on="" to="" suggest="" that="" such="" behavior="" supported="" general="" biological="" principles="" of="" social="" evolution.="" in="" short,="" hamilton="" had="" given="" both="" darwin="" and="" the="" selfish-gene="" thinkers="" a="" unified="" way="" of="" comprehending="" the="" problem="" of="" altruism.="" he="" had="" worked="" out="" how="" fitness="" worked="" on="" individuals="" other="" than="" the="" actor.="" this="" became="" known="" as="" hamilton's="" principle,="" and="" it="" is="">

Still, not everyone is happy denying the role of group selection as a player in evolution. Although Dawkins, Williams, and other critics of group selection admit that natural selection can work on groups in principle, their stance is that selection pressures at the individual level are always stronger than those at the group level. Not all evolutionary biologists agree. David Sloan Wilson and Edward O. Wilson, in a review of the history of the rise and fall of group selection theory, conclude that the last forty years of research have provided new empirical evidence that supports the theory of group selection and its theoretical plausibility as an evolutionary force. "The problem is that for a social group to function as an adaptive unit, its members must do things for each other. Yet, these group-advantageous behaviors seldom maximize relative fitness within the social group. The solution according to Darwin is that natural selection takes place at more than one level of the biological hierarchy. Selfish individuals might out-compete altruists within groups, but internally altruistic groups out-compete selfish groups. This is the essential logic of what has become known as multilevel selection theory."3 David Sloan Wilson suggests that group selection is not just a significant evolutionary force but can sometimes be the dominating evolutionary force. In a letter to eSkeptic, he writes: "It turns out that evolution takes place not only by small mutational change, but also by social groups and multi-species communities becoming so integrated that they become higher-level organisms in their own right."*

Although this is a highly controversial question, we can let the evolutionary biologists duke it out. Let us merely come away with the fact that our social behavior has biological origins.

The deep biological forces at work in producing our social mind will become evident as we consider how we got to this place. Even more tantalizing is the possibility that all those social relationships we now worry about so intensely are merely by-products of behavior originally selected to avoid our being eaten by predators. Natural selection mandated us to be in groups in order to survive. Once there, we construct our "meaningful" as well as our "manipulative" social relationships, with our interpretive minds ever busy dealing with the stuff around us, most of which involves our fellow humans. While those human social relationships become central to our mental life, indeed become in many cases the raison d'etre of our lives, it is all generated by a process secondary to the real reason we fall into social groups. We now think about others all the time because that is how we are built. Without all those others, without our alliances and coalitions, we die. It was true, as we shall see, for early humans. It is still true for us.

What would you think about if you were the only person on earth? Maybe your next meal? However, you wouldn't be thinking about who might help you get that meal or with whom you might share that meal. You might think about how to avoid being a meal yourself, but there would be no one to help you watch for predators.

We are social to the core. There is no way around the fact. Our big brains are there primarily to deal with social matters, not to see, to feel, or to cogitate about the second law of thermodynamics. We all can do these personal and more psychological actions. We can develop rich theories about our personality, but we do so as a result of functioning in the social world. All of that comes along after the fact. And the fact is, in order to survive and prosper, we had to become social. So, understanding how we got here requires reviewing evolutionary biology, and to understand the biology of our current social abilities, which include phenomena such as altruism, we need to remind ourselves how evolution works.

EVOLUTION, NATURAL SELECTION, AND THE PUSH TOWARD SOCIAL BEHAVIOR.

Charles Darwin and Alfred Wallace* both observed that although species have a high potential for reproduction and populations should multiply exponentially, they don't. Except for occasional fluctuations, populations remain stable. After all, natural resources are limited and remain constant in a stable environment.* Thus more individuals are born than the resources can support, and this results in compet.i.tion for those resources. Darwin and Wallace also observed that within each species, the individuals in the population vary. No two are exactly alike, and many of the traits that are variable are inherited. They concluded that the chances for survival weren't random, but varied with the heritable characteristics. According to the laws of natural selection, for any characteristic to be selected in a compet.i.tive environment, it has to provide a survival advantage to the individual. That advantage must manifest itself in a greater number of surviving offspring. The characteristic may allow the individual to be more successful at finding food (so he is stronger and healthier and hence can reproduce more and longer), at mating (so he will reproduce more), or at fighting off predators (so he will live longer and be able to reproduce more). These characteristics are coded for in the individual's genes and are pa.s.sed on to the next generation. Thus, genes that code for any behavior that increases reproductive success will become more prevalent in the population.

Compet.i.tive pressures are affected by climate, geography, and other individual animals, both within the species and from different species. Changes in climate and geography, such as a volcanic eruption that also affects the climate, can cause changes in food resources, making them either more or less plentiful. Social compet.i.tion arises within a species, either for food resources or s.e.xual partners. Different species have evolved to deal with food compet.i.tion in different ways. Some share and some don't.

One of the questions that puzzled Darwin about his theory was concerning altruistic behavior. It didn't make sense that an individual would share-would ever provide anything to another individual that would decrease its own reproductive success to the benefit of another's. Yet this happens frequently in species that live in groups. As I already mentioned, William Hamilton in 1964 came up with the theory of kin selection, which explains this behavior. Altruistic behavior could evolve if the benefiting individuals were genetically related to the provider. Parents will sacrifice for their children, who share 50 percent of their DNA; individuals also share 50 percent of their DNA with their siblings; their grandchildren and their nieces and nephews share 25 percent of their DNA. Helping your close relatives survive and reproduce also pa.s.ses your genes on to the next generation. It doesn't matter how the genes get pa.s.sed, just so they do.

Kin selection does not explain all cases of altruism, however. Why would anyone do a favor for a friend? This question remained unanswered until Robert Trivers, professor of anthropology at Rutgers University, figured it out. If an individual does a favor for an unrelated individual and is sure it will be returned at a later date, then that could provide a survival advantage.4 This presupposes several things, of course. One is that an individual can specifically recognize another individual and has the ability to remember that a favor was done. Another is that the two live in close enough contact that predictable occasions will arise to get repaid. They also have to be able to evaluate the cost of the favor and make sure that the one they get in return is of equal value. This is called reciprocal altruism, and it is very rare in the animal world.*

The difficulty arises because there is a time lag between when one individual performs a favor and when the second reciprocates. The time lag could allow for cheating. If the second individual is not reliable, it is not in the interest of the first to cooperate with him, and the possibility of a cooperative system falters. Species that practice reciprocal altruism also have mechanisms to identify cheaters,5 otherwise the behavior would never have survived. As a consequence, strict Darwinian principles can help explain such phenomena as altruism. During the Enron fiasco, the cry was "Follow the money." In biology, follow the genes.

This leaves one further problem: The old question, why leave a tip at a restaurant that you will never return to? We will get to this question later, and it may have to be explained by group selection!

s.e.xual Selection and Social Groups.

Some adaptations enhance success in reproductive compet.i.tion. The cla.s.sic example is the peac.o.c.k's tail. Common sense would tell you that it could only be a hindrance towing a huge tail around. How could that possibly be adaptive? However, any bird that could survive with a big tail must surely be an attractive mate: strong and healthy and wily. That big tail is straight from Madison Avenue, a great advertis.e.m.e.nt campaign that pays off with more mates. The birds with the big tails have more offspring.

The peac.o.c.k's tail confers an advantage for s.e.xual selection, the term for the social dynamics involved in mate selection and reproduction. That tail is known as a fitness indicator. The higher the cost of a fitness indicator to the individual, the more reliable it is. It costs the peac.o.c.k a lot of energy to carry around and maintain the big tail. He cannot counterfeit it; it is a reliable fitness indicator. A guy with a new Chevy may well have counterfeited his fitness indicator; he could have bought it with 0 percent financing, no credit, and a low monthly payment. However, a guy with a Lamborghini has an expensive, high-maintenance car that cannot be purchased without good credit, and it reliably indicates his resources. A Lamborghini is a good fitness indicator, but a Chevy is not.

Trivers also helped us realize that the underlying behavior of s.e.xual selection all revolves around parental investment. Parental investment is "any investment by the parent in an individual offspring that increases the offspring's chance of surviving at the cost of the parent's ability to invest in other offspring."6 Hence, in any species, the s.e.x with the higher potential rate of reproduction is more concerned about mating as often as possible (to get as many of their genes into the next generation as possible), and the s.e.x with the lower reproductive potential is more concerned about parental care, to make sure that the few offspring they have will survive.7 In 95 percent of mammalian species, there is a large difference between males and females as to the efforts invested in mating and parenting.8 Females have limited reproductive time, due to pregnancy (internal gestation) and care of young offspring (lactating).9 And we all know about males. They are ready to reproduce at a moment's notice.

The s.e.x that has a higher parental investment and lower reproductive potential, usually the female, tends to be more fussy about mate selection.10 They have more to lose by making a bad decision (less fit offspring that might not be able to reproduce themselves). Female choice of mating partners has influenced physical (the peac.o.c.k's tail), behavioral, and social evolution in males. It intensifies both male-male compet.i.tion for mating partners and female-female compet.i.tion. s.e.xual selection can lead to "runaway s.e.xual selection." This means the genes that are being selected for are also doing the selecting, setting up a positive feedback loop. Let me give you a simplified example of how this works.

Say you have a population of rabbits with short ears. Along with other characteristics, the trait for ear length is variable and heritable. The male rabbits have little parental investment; they mate as often as they can with whomever they can. Now, although they all have short ears, Rex's ears are a little longer than the others'. For some reason, a couple of the females have evolved a preference for longer ears, so they choose to mate with Rex. Their offspring are not only going to have longer ears but also will have the preference for longer ears. The traits have become genetically correlated when genes for different traits (long ears and the preference for long ears) end up in the same bodies. A positive feedback loop has been established. The more females who select for long ears, the more males and females there will be who have long ears as well as the preference for long ears. Runaway selection occurs.

Big Brains, Big Appet.i.tes, and the Hunt.

The third factor in our drift toward being social seems to grow out of our need to nourish our ever-growing big brains. Hunting, herding, hiding, and hustling all lead to our social instincts and ultimately our domination. One way to compare brain sizes was used by David Geary, now professor of psychology at the University of Missouri, who has estimated what is called the encephalization quotient, or EQ,* of various hominid species as a percentage of the EQ of modern humans. He has shown that there is a relentless progression of increasing relative brain size during the evolution of hominids.11 What caused this progression?

Traditional theories propose that ecological problems and problem solving have driven changes in the brain. Harry Jerrison, paleoanthropologist and emeritus professor of psychiatry at the University of California at Los Angeles, noted the brain sizes of predators and prey have increased back and forth in t.i.t-for-tat fashion over the last sixty-five million years.12 Because humans use tools for hunting (predation), it was a.s.sumed that production and use of tools were what was driving the increase in brain size. However, this theory didn't fit the facts.

Thomas Wynn, an anthropologist at the University of Colorado, states, "Most of the evolution of the human brain, the presumed anatomy of intelligence, had occurred prior to any evidence for technological sophistication and, as a consequence, it appears unlikely that technology itself played a central role in the evolution of this impressive human ability."13 That is not to say that the ecology was not the early driving force for increased brain size, just that tool use was not.

Big brains are expensive and require more energy (food) than small ones, and there is evidence that early hominids did become more efficient at hunting and foraging and were thus able to occupy a wider range of ecologies. Anthropologists John Tooby and Irven Devore argue that hunting was very important in human evolution. As Steven Pinker puts it, "The key is to ask not what the mind can do for hunting, but what hunting can do for the mind."14 And what it can do is supply meat, a complete protein and a great source of energy for the greedy brain. Pinker points out that in the land of mammals, those that are carnivores have bigger relative brain sizes.

Richard Wrangham, our chimp man, thinks having meat was not enough; one had to be able to eat it efficiently. Although the diet of a chimpanzee contains about thirty percent monkey meat, it is very tough and it takes so long to chew that any advantage it might have in total calories is offset by the time it takes to eat. That is, an equivalent amount of time eating plants would have supplied the same number of calories. Wrangham not only spent many hours observing chimp behavior, he also sampled their cuisine, and he wasn't impressed. It was tough, fibrous, and very difficult to chew. He could not understand how any ape, eating the diet of a chimp-raw fruits, leaves, tubers, and monkey meat-could ama.s.s enough calories to supply the metabolically expensive big brain. Chimps spend almost half their waking hours chewing, interspersed with short periods of rest, which allow their stomachs to empty, but not enough time to go on extended hunts. There just wasn't enough time in the day to eat enough calories.

There also was another quandary. Chimps have big teeth and powerful jaws, as did the early Australopithecines and h.o.m.o habilis. h.o.m.o erectus was a different story. His jaws and teeth were smaller, while his brain was twice as large as his predecessor h.o.m.o habilis. What was he eating to get the calories to drive and maintain the brain expansion with those wimpy teeth and jaws? Not only that, h.o.m.o erectus had a smaller rib cage and abdomen, meaning that it could not hold as large of a digestive tract as h.o.m.o habilis. In fact modern man has a 60 percent shorter digestive tract than predicted for a great ape of our size.

Starting into the fire, Wrangham came up with a radical idea: those early humans were eating barbeque!15 Cooked food has several advantages over raw food.16 It actually has more calories, and is softer, so you don't have to spend so much time and energy chewing: more calories, less time, less effort (not unlike the modern concept of fast food). In fact, the softer the food, the more calories there are available for growth, because it takes less energy to consume and digest it.17, 18 Some anthropologists have objected to this theory because the oldest evidence for fire that they have found is from 500,000 years ago, but there are some hints surfacing that fire was on the scene much earlier, maybe even 1.6 million years ago, just about the time that h.o.m.o erectus made his appearance. Wrangham suggests that h.o.m.o sapiens are biologically adapted to eat cooked food.15 He thinks that cooking food drove the expansion of the brain by increasing calories and decreasing the amount of time it takes to ingest them. This freed up more time for hunting and socializing.

There are those, however, who think the story hinges on the fatty acids in the brain. The long-chain polyunsaturated fatty acid docosahexaenoic acid (DHA) was required for the expansion of the hominid cerebral cortex during the last one to two million years. Michael Crawford and coworkers at the Inst.i.tute of Brain Chemistry and Human Nutrition, University of North London, think that because biosynthesis of DHA from its dietary precursor (alpha-linolenic acid, or LNA) is relatively inefficient, expansion of the human brain required a plentiful source of preformed docosahexaenoic acid.19 The richest source of DHA is the marine food chain, while the savanna environment offers very little of it. Tropical freshwater fish and sh.e.l.lfish have long-chain polyunsaturated lipid ratios more similar to that of the human brain than any other food source known. Crawford concludes that h.o.m.o sapiens could not have evolved on the savannas but instead were holed up at the beach, gathering along the sh.o.r.eline.20 Nutrients gained in this manner contributed to increasing brain size and intelligence, which allowed our ancestors to forage and fish more effectively.21 But anthropologists Bryce Carlson and John Kingston at Emory University are not convinced. They do not think the biochemistry implies any such thing. They point out that the key premise of this perspective-that biosynthesis of DHA from LNA is not only inefficient but also insufficient for the growth and maturation of an encephalized brain-is not well supported. To the contrary, evidence suggests that consumption of LNA available in a wider variety of sources within a number of terrestrial ecosystems is sufficient for normal brain development and maintenance in modern humans and presumably our ancestors.22 By moving out into the more open landscapes-open woodlands, savannas, and gra.s.slands-the early hominids not only had more animals to hunt, they also became more of a target for predators themselves. There is a growing consensus that a major factor in developing larger brains was the banding together in social groups, which made hunting and gathering more efficient and also provided protection from other predators.23 There are two ways to outfox predators. One is to be bigger than they are, and the other is to be part of a larger group. (Gary La.r.s.en, in a Far Side cartoon, presented a third method: All you need is a buddy who runs slower than you do.) The more individuals in the group, the more eyes are on the lookout. Predators have an attack range that depends on their speed and their style of killing. As long as you spot them and stay out of their range, you are fine. Also, if you have compatriots who will come to your aid when you are in trouble, a predator is less likely to attack. Herd animals are not known for the buddy system, but the social primates are. Individuals that banded together had a higher survival rate. And this brings us to social groups.

So three intertwined factors triggered the push toward our social mind: natural selection, s.e.xual selection, and the consequences of needing more food to nourish our growing brains. Once social abilities became part of human brain architecture, other forces were unleashed, which in turn contributed to our growing brain size.

ORIGINS OF SOCIAL GROUPS.

In 1966, Alison Jolly, a behavioral biologist trained in America and now at the University of Winchester in the United Kingdom, concluded a paper about lemur social behavior by stating, "Primate social life provided the evolutionary context of primate intelligence."24 In 1976, Nicholas Humphrey, without knowledge of Jolly's paper, also concluded, "I argue that the higher intellectual faculties of primates have evolved as an adaptation to the complexities of social living."25 He was suggesting that the ability to predict and manipulate another's behavior would give a survival advantage and would lead to increased mental complexity. Upon these and a few other papers, the theory of Machiavellian intelligence was hatched.

The hypothesis was first presented by Richard Byrne and Andrew Whiten at the University of Saint Andrews, Scotland, and they suggested that the difference between primates and nonprimates is the complexity of their social skills: Living in complexly bonded social groups is more challenging than dealing with the physical world, and the cognitive demands of this social life selected for increases in brain size and function.26 "Most monkeys and apes live in long-lasting groups, so that familiar conspecifics are major compet.i.tors for access to resources. This situation favours individuals that can offset the costs of compet.i.tion by using manipulative tactics, and skillful manipulation depends on extensive social knowledge. Because compet.i.tive advantage operates relative to the ability of others in the population, an 'arms race' of increasing social skill results, which is eventually brought into equilibrium by the high metabolic cost of brain tissue."23 Poor Machiavelli. Perhaps he was the ultimate sociologist, but his name has pejorative connotations, so the messenger was shot. The theory is now called the social brain hypothesis.

Another related hypothesis on increasing brain size was suggested by Richard Alexander, a professor of zoology at the University of Michigan. He focused on intergroup rather than intragroup compet.i.tion and proposed that the main predator became other groups of hominids. This caused an arms race of strategizing and weapon invention: "Humans had in some unique fashion become so ecologically dominant that they in effect became their own princ.i.p.al hostile force of nature, explicitly in regard to evolutionary changes in the human psyche and social behavior."27 WHY IS SOCIAL GROUP SIZE LIMITED?.

Support for some type of social component for the big brain has come most notably from the very clever anthropologist Robin Dunbar at the University of Liverpool. Each type of primate tends to have a social group size consistent with other members of the same species. Dunbar has correlated brain size with social group size in primates and apes, and found there are two different but parallel scales, one for apes and one for the other primates. Both show that the bigger the neocortex, the larger the social group. However, the apes required a bigger neocortex per given group size than the other primates.28 They seem to have to work harder to maintain their social relationships.

But why is social group size limited? Does it have something to do with our cognitive abilities? Dunbar proposes five cognitive abilities that could be limiting social group size: the ability to interpret visual information to recognize others, the memory for faces, the ability to remember who has a relationship with whom, the capacity to process emotional information, and the ability to manipulate information about a set of relationships. He maintains that it is the last cognitive skill, the one that deals with social issues, that underlies the limitation on group size. He points out that vision doesn't seem to be the problem, because the neocortex has continued to grow, whereas the visual cortex has not. Memory isn't the problem; people can remember more faces than their predicted cognitive group size. Emotion doesn't seem to be the problem; in fact there has been a reduction in the emotional centers of the brain. According to Dunbar, it is the ability to manipulate and coordinate information and social relationships that is limiting social group size. One can only handle a finite amount of manipulation and relationships!

Ways to measure social skill and social complexity have been hard to find. Currently five different aspects of social behavior have been correlated with neocortex size in primates. The first to be identified was social group size.29, 30 Others are: Grooming clique size-the number of individuals with whom an animal can simultaneously maintain a cohesive intimate relationship that involves physical grooming.31 The degree of social skill required in male mating strategy. This indicates that the advantages of individual male rank and power appear to be offset by social skill: You don't have to be the big cheese to get the girl; you can also get her by charm.32 The frequency of tactical deception-the ability to manipulate others in the social group without the use of force.23 The frequency of social play.

Dunbar looked for ecological indices that might also correlate with brain size: the proportion of fruit in the diet, the home range size, day journey length, and foraging style. There was no correlation between these and neocortex size. He concluded that most likely the increasing size of social groups was driven by the ecological problem of predator risk, and the pressures and complexities of living in the increasingly large social groups drove brain size expansion.34 So we ended up with these big brains all because we didn't want to be the plat du jour? Let's look at these five social skills and see if any aspect of them is unique to humans.

SOCIAL GROUP SIZE FOR HUMANS.

While the observed social group size of chimpanzees is 55, the social group size that Dunbar calculated from the neocortex size of humans is 150. How can that be, when we now live in huge cities, often with millions of people? However, think about it. Most of those people you never even have cause to interact with. Remember: Our ancestors were hunter-gatherers, and people didn't start to settle in one place until agriculture was developed about ten thousand years ago. Today the typical size of hunter-gatherer clans, related groups that gather together once a year for traditional ceremonies, is 150. This is also the size of traditional horticultural societies and modern-day Christmas card lists in personal address books.35 It turns out that 150 to 200 is the number of people who can be controlled without an organizational hierarchy. It is the basic number used in military units where personal loyalties and man-to-man contact keep order. Dunbar states that it is the upper limit of the size of modern business organizations that can be run informally.36 It is the maximum number of people an individual can keep track of, whom he can have a social relationship with and would be willing to help with a favor.

SOCIAL GROOMING: THE ROLE OF GOSSIP.

Gossiping has a bad reputation, but researchers who study gossip have not only found it to be universal,37 they have found that it is beneficial, that it is the way we learn to live in society. Dunbar thinks gossip is the human equivalent of social grooming in other primates (and remember, the size of the grooming group correlates with relative brain size). Physical grooming takes up much of a primate's time. The primates that spend the most time grooming are chimps, who do it up to 20 percent of the time.38 At some point during the evolution of the hominids, as groups became larger, an individual would need to groom more and more other individuals in order to maintain relationships in the larger group. Grooming time would cut into the time that was needed to forage for food. This is when, Dunbar argues, language began to develop.39 If language began to subst.i.tute for grooming, one could "groom," that is to say, gossip, while doing other things, such as foraging, traveling, and eating. This could be how talking with your mouth full began.

However, language can be a double-edged sword. The advantages of language are that you can groom several people at once (more efficient) and you can get and give information over a wider network. However, the disadvantage is that you are vulnerable to cheaters. With physical grooming, an individual invests high-quality personal time. That cannot be faked. With language, a new dimension has been added: liars. One can tell stories displaced in time, so their veracity is difficult to a.s.sess, and while grooming is done among a group, where it is visible and verifiable to all, gossiping can be done in private, and its veracity is not challenged. But language can also help you out with this problem. You may be warned by a friend about a previously bad experience with a certain individual. As a social group gets larger and more dispersed, cheaters or free riders become harder to keep track of. Gossip may have evolved partly as a way to control the slackers.40, 41 Various studies have found that, on the average, humans spend 80 percent of their waking time in the company of others. We average six to twelve hours per day in conversation, mostly one-on-one with known individuals.42 What has been found out shouldn't come as any surprise to you. Nicholas Emler, a social psychologist at the London School of Economics, has studied the content of conversations and learned that 80 to 90 percent are about specific named and known individuals, which is to say, small talk. Impersonal topics, although they may involve personal opinions on art, literature, religion, politics, and so forth, form only a small part of the total. This is true not only about chance meetings in the grocery store but also at universities and corporate lunches. You might think that the world's problems are being discussed and settled over power lunches, but it is really Bob's tee time, Bill's new Porsche, and the new secretary that are getting 90 percent of the air time. If you think this is an exaggerated statistic, then think about all those annoying cell phone conversations you have overheard. Have you ever heard anyone talking about Aristotle or quantum mechanics or Balzac at the table next to you or in the grocery line?

Other studies show that two-thirds of the content of conversations are self-disclosure. Of these, 11 percent are about states of mind (my mother-in-law is driving me nuts) or body (I really want that liposuction). The rest are about preferences ("I know it's weird, but I really like LA"), plans ("I am going to start exercising on Friday"), and the most talked about, doings ("I fired him yesterday"). In fact doings is the biggest category of conversations about others.42 Gossip serves many purposes in society: It fosters relationships between gossip partners,43 satisfies the need to belong and be accepted by a unique group,37 elicits information,44 builds reputations (both good and bad),43 maintains and reinforces social norms,45 and allows individuals to evaluate themselves through comparison with others. It may enhance status in a group, or it may just entertain.46 Gossip allows people to express their opinions, ask advice, and express approval and disapproval.

Jonathan Haidt, a psychologist at the University of Virginia who studies happiness, writes that "Gossip is a policeman and a teacher. Without it, there would be chaos and ignorance."47 It is not just women who gossip, although men like to call it "exchanging information" or "networking." The only time when men spend less time gossiping than women do is when women are present. Then more lofty subjects are discussed for about 15 to 20 percent of the time. The only difference between male and female gossip is that men spend two-thirds of the time talking about themselves ("and when I reeled that sucker in, I swear it weighed twenty-five pounds!"), whereas women spend only one-third of the time talking about themselves, and are more interested in others ("and the last time I saw her, I swear she had gained twenty-five pounds!").48 Beyond the content of conversations, Dunbar also discovered that conversation groups are not infinitely large but are usually self-limiting to about four individuals. Think about the last party you went to. People drift in and out of conversation groups, but once you go over four people, they do tend to break up into two conversations. He says it may be coincidence, but he suggests a correlation with chimp grooming. If you take a conversation group of four persons, only one is talking and the other three are listening, or in chimp lingo, are being groomed. Chimps have to groom one-on-one, and their maximum social group size is 55. If we can groom three at a time, as indicated by conversation group size, then if you multiply our three grooming partners by 55, you get 165-close to our social group size that Dunbar calculated from the neocortex size of humans.

TACTICAL DECEPTION.

In working the gossip mill, a person is involved not only in information exchange but perhaps in manipulation and deceit. He may be deceiving his gossip partners in essence because he isn't really talking with them to find out how they are doing; he may be mining information for his own purposes. He might even make something up so as to have more gossip to barter. These are two different issues. Let's start with exchange. I mentioned before, in order for reciprocal exchange to work, cheaters have to be identified. Otherwise, cheaters, who benefit without paying the cost, would eventually take over, and reciprocal exchange couldn't sustain itself.

Although there are cultural differences among groups of people, there are many universal behaviors.49 As we have seen, we can trace some of these behaviors back to our common ancestor with the chimps and beyond, and some are qualitatively different. The field of evolutionary psychology attempts to explain mental traits, such as memory, perception, or language, as adaptations-products of natural or s.e.xual selection. It looks at psychological mechanisms in the same way that biologists look at biological mechanisms.

Evolutionary psychology suggests that cognition has a functional structure that has a genetic basis, just like hearts, livers, and immune systems, and has evolved by natural or s.e.xual selection. Like other organs and tissues, these psychological adaptations are universally shared within a species, and they enhance survival and reproduction. Some traits are not controversial, such as vision, fear, memory, and motor control. Others are controversial but are becoming less so, such as language acquisition, incest avoidance, cheater detection, and s.e.x-specific mating strategies. Evolutionary psychologists explain that a brain, at least in part, is made up of modules, which have developed specific functional purposes that are innate and have been selected for. Leda Cosmides, one of the first in this field, describes the search for these functions: When evolutionary psychologists refer to "the mind," they mean the set of information-processing devices, embodied in the human brain, that are responsible for all conscious and nonconscious mental activity, and that generate all behavior. What allows evolutionary psychologists to go beyond traditional approaches in studying the mind is that they make active use in their research of an often overlooked fact: That the programs comprising the human mind were designed by natural selection to solve the adaptive problems faced by our hunter-gatherer ancestors. It leads one to look for programs that are well-engineered for solving problems such as hunting, foraging for plant foods, courting mates, cooperating with kin, forming coalitions for mutual defense, avoiding predators, and so on. Our minds should have programs that make us good at solving these problems, whether or not they are important in the modern world.50 There are very practical reasons for looking at our behavior and abilities from an evolutionary standpoint. Cosmides points out: By understanding these programs, we can learn how to deal more effectively with evolutionarily novel circ.u.mstances. Consider, for example, that the only information available to hunter-gatherers about probability and risk was the frequency with which they encountered actual events. It looks like our "stone age mind" has programs designed to acquire and reason well about frequency data. Knowing this, evolutionary psychologists are developing better ways of communicating complex modern data about statistics.

Let's say you have a positive mammogram. How likely is it that you actually have breast cancer? The typical way of presenting the relevant data-in percents-makes this difficult. If you said that 1% of women randomly screened have breast cancer, and all of these test positive, but there is a 3% false alarm rate, most people mistakenly think a positive mammogram means they have a 97% chance of having breast cancer. But let me give you the same information in absolute frequencies-an ecologically valid information format for a hunter-gatherer mind: Out of every 1000 women, 10 have breast cancer and test positive; 30 test positive but do not have breast cancer. So: out of every 1000 women, 40 will test positive, but only 10 of these will have breast cancer. This format makes it clear that, if you had a positive mammogram, your chance of having breast cancer is only 1 in 4...that is, 25%, not 97%.50 Detecting Cheaters.

Cosmides also came up with an experiment that she thinks demonstrates that the human mind has a special module designed to detect individuals who cheat in social exchange situations. She uses the Wason Test,* which asks you to look for potential violations of a conditional rule: if P, then Q. Many forms of this test have been devised to ascertain whether or not humans have specialized cognitive machinery for social exchange. Let's see how you do with it: There are four cards on a table. Each card has a letter on one side and a number on the other. Currently you can see R, Q, 4, and 9. Turn over only those cards that you need to in order to prove whether the following rule is true or false: If a card has an R on one side, then it has a 4 on the other. Got it? What's your answer?

The answer is R and 4. OK, now try this one:.

There are four people sitting at a table. One is sixteen, the second is twenty-one, the third is drinking c.o.ke, and the fourth is drinking beer. Only those over twenty-one can drink beer legally. Who should the bouncer check to make sure the law isn't being broken? That one is easier isn't it? The answer is the sixteen-year-old and the beer drinker.

Cosmides has found that people have a hard time with the first type of question; only 5 to 30 percent of people get this one right, whereas with the second one, 65 to 80 percent of people get it right-not just at Stanford where she first tried it, but all over the world, from the French to the Shiwiar of the Ecuadorian Amazon, and not just adults, but three-year-olds as well. Whenever the content of a problem asks you to look for cheaters in a social exchange situation, people find it simple to solve, whereas if it is posed as a logic problem, it is more difficult to solve.51 After many more experiments across cultures and age groups, Cosmides has found in addition that cheater detection develops at an early age, operates regardless of experience and familiarity, and detects cheating but not unintentional violations. She thinks that this cheater detection ability is a component of a universal human nature, designed by natural selection to produce an evolutionally stable strategy for conditional helping.

There is even neuroanatomical evidence. This comes from a patient, R.M., who has focal brain damage that has caused impairment in his cheater detection, but who has entirely normal reasoning on similar tasks that do not involve social exchange.52 Cosmides says, "As humans, we take for granted the fact that we can help each other by trading goods and services. But most animals cannot engage in this kind of behavior-they lack the programs that make it possible. It seems to me that this human cognitive ability is one of the greatest engines of cooperation in the animal kingdom."50 We are not the only ones who can detect cheaters in social exchanges. It has been shown to exist to a limited degree in brown capuchin monkeys, in experiments done by Sarah Brosnan and Frans de Waal.53 However, animals involved in reciprocal exchange make approximations. Humans want to be sure they are giving and getting the equivalent amount; approximations won't suffice. Indeed, Marc Hauser at Harvard University thinks that our mathematical abilities evolved with the emergence of social exchange systems.54 Cheating the Cheaters.

Can you cheat the cheater detection system? Probably not, as Dan Chiappe, a psychologist at the University of Toronto, has found. He showed that in social contract situations, people rated cheaters more important to remember than cooperators, looked at cheaters longer, remembered their faces better, and were more likely to remember social contract information about them.55 When cheaters have been detected, there are two things that can be done with them: Either you avoid them, or you punish them. Isn't it easier just to avoid them? To punish a cheater costs the punisher time and effort. What's to be gained? Recently Pat Barclay, from Cornell University, has done a laboratory study showing that in games with repeated encounters, players who punish cheaters gain trust and respect