Homo Mysterious: Evolutionary Puzzles of Human Nature (45 page)

If the sexual selection theorists are correct, one wonders as well about the situation of ancestral women. Although both sexes can be expected to have exercised preference for smart sexual partners (in fact, this was likely true even if survival selection rather than sexual selection was the driving force), women would have been uniquely stuck with a major
negative
consequence of such a choice. Women, not men, get pregnant and give birth. And because of our species’ penchant for bipedalism,
ⁱⁱ
the human birth canal has been substantially and dangerously narrowed over evolutionary time, such that selection for increased head size has literally bumped up against the anatomically mandated narrowing of women’s pelvic girdle. Most quadrupeds drape their internal organs from their backbones, like salamis hanging in a butcher shop. But with bipedalism, the human pelvis has necessarily rotated, partly to provide basinlike support for our abdominal organs but in the process, restricting the birth canal. As a tragic result, one of the most common sources of perinatal morbidity and mortality is “cephalopelvic disproportion,” when the baby’s head is too large for the mother’s pelvic opening.

Earlier, we encountered a Goldilocks hypothesis, whereby men were hypothesized to choose women whose breasts and thus
reproductive prospects were “just right.” When it comes to female choice of intelligent men as sexual partners, Goldilocks just might have been at it again, generating babies whose heads are large—probably as large as possible. But not too large. Just right.

Other ideas also concern themselves with a possibly disproportionate role of women—specifically, mothers—in selecting for human intelligence, aside from choosing their reproductive partners. For example, if maternal intelligence contributes substantially to reducing childhood and infant mortality, this could itself select for greater intelligence—for people generally and for intelligence in women most especially.
¹¹
This smart-mother hypothesis requires that childhood mortality rates are otherwise high, which they certainly were during most of our evolutionary history. It also assumes an inverse correlation between maternal IQ and childhood mortality, which also appears valid,
¹²
although this line of thought is inconsistent with the fact that there is currently an inverse relationship between maternal IQ and reproductive success in modern technological societies.
¹³
One can nonetheless argue that such a correlation was likely obtained during the 99.99% of our evolutionary past when most of our humanness evolved.
ⁱⁱⁱ

When discussing a different evolutionary mystery—menopause—in
Chapter 3
, we looked into the possibility that the prolongation of human childhood may have been intimately connected to the termination of women’s reproduction and the consequent ability and inclination of grandmothers in particular to help care for their grandchildren. It may be equally valid to reverse this association and consider that human intelligence may owe much to our prolonged childhood, which is lengthier than that of any other primate.
¹⁴
If so, then our intelligence also owes much to mothers as well as grandmothers, whose attentiveness would have helped select for our extended juvenile period, a time during which we almost literally fill our brains with the stuff of experience and thus of intelligence (fathers, too, or at least so I’d like to think).

Assortative mating—in which “like prefers like”—could amplify this tendency: Males who are smarter could presumably have been more effective resource and protection providers as well as teachers of their children. If they mated with females who were especially good at keeping their offspring safe, as well as obtaining and preparing optimum nutrition and also providing them enhanced learning opportunities, the resulting positive feedback could have contributed substantially to the evolution of intelligent offspring. This effect may well have become even more pronounced as early human ancestors migrated “out of Africa,” since inclinations leading to survival and success in the Pleistocene environment where much human evolution occurred would presumably have been strongly selected for and could well have become “instinctively” fixed. It is when our ancestors encountered a new environment (Ice Age Europe and Asia, the discovery of agriculture, urbanization, and so forth) that maternal as well as paternal IQ would have become especially relevant.

When we referred previously to “social competition” as a possible driver of increased human brain size and intelligence, the implication—as with hypotheses invoking primitive warfare—was that the key interactions were those taking place between competing groups. There is another array of emerging hypotheses that also point toward social competition, but of another sort: within-group and mostly nonviolent. The term of art is social intelligence,
¹⁵
and in its sneakier form, “Machiavellian intelligence.”
¹⁶

The key point here is that social living is a two-edged sword. On the one hand, it provides many opportunities not available to those whose lives are more solitary: taking advantage of strength in numbers when it comes to catching prey (think about wolves pulling down a moose), keeping predators at bay (including perhaps other groups of the same species), sharing information and expertise, and so forth. But on the other hand, social life has its downsides: the need to share food or other important resources, increased risk of disease transmission, and so forth. It also sets up
numerous hurdles as well as opportunities for success, since social living establishes its own complicated array of challenges.

Zoologist Richard D. Alexander put it succinctly (albeit with perhaps more certainty than such a complex subject warrants):

The real challenge in the human environment throughout history that affected the evolution of the intellect was not climate, weather, food shortages, or parasites—not even predators. Rather, it was the necessity of dealing continually with our fellow humans in social circumstances that became ever more complex and unpredictable as the human line evolved.
¹⁷

Natural selection operates for the most part on the reproductive success of individuals and their constituent genes rather than for the good of the group as a whole. As a result, there is a constant tug-of-war among individuals (and their genes), each struggling to maximize its payoff, and not necessarily someone else’s. This issue is ameliorated, but definitely not eliminated, by the fact that maximum success is often achieved by cooperating rather than competing—because insofar as cooperation is motivated by the payoff available to each participating individual, every individual is nonetheless motivated by considerations of personal advantage. In other words, even while cooperating, individuals will have been selected to maximize their benefit in doing so. If this sounds Machiavellian, then welcome to the Machiavellian hypothesis for the evolution of intelligence, which basically says that intelligence has arisen because of the payoff to individuals who are able to evaluate social situations and come up with their personally optimal responses. And this process in turn is recursive, since it conveys a benefit to those who are able to detect the self-serving maneuvers of others and use them to enhance one’s own situation—or at least, to keep one’s payoff from being diminished as a result.

The result is survival and success of the socially adept and thus mutually beneficent, as well as of the cunning and manipulative and thus diabolically self-serving. For example, social intelligence promotes differential reproduction of those who are able to establish useful coalitions to defend their interest and compensate, perhaps, for a lack of size or strength by making strategically helpful alliances with others who are equally intelligent.

Nonhuman primates engage in an almost dizzying variety of complicated social calculations, including short-term bonds for mating as well as long-term associations (essentially, friendships) based on the status, need, and potential contributions of all participants. A dazzling series of field experiments conducted among free-living baboons, for example, showed that individuals are able to assess social dominance as well as the genetic relationships of others in their troop and to keep these traits in mind, juggling the pros and cons of various actions accordingly.
¹⁸

For social intelligence to be directly selected for, it is also necessary that social success correlate positively with reproductive success, something that seems intuitively likely, and that has been demonstrated convincingly in a research report whose title well describes its key finding: “Social Bonds of Female Baboons Enhance Infant Survival.”
¹⁹
In short, individuals who succeed in effectively navigating the complexities of social life are those who succeed in getting copies of their genes projected into the future. Although our antecedents were not baboons, it seems more than likely that a similar process occurred in ancestral human beings.

Social success—and thus reproductive success—likely correlates double-fold with the ability to employ high levels of rational thought. Of these payoffs, the obvious one relates to the direct benefits of simply being smart: ability to anticipate future events, deal with present ones, adjust one’s behavior to that of one’s colleagues and competitors, and so forth.

But a possible secondary benefit might also be involved: the payoff in terms of social prestige and dominance of simply being able to defeat one’s enemies (and friends) when it comes to argumentation. Thus, the possibility exists that rationality and the ability to express one’s most cogent thoughts in the social arena have evolved not because such a capability permits the speaker and listener to approach greater insight into the actual nature of the world, but rather, to help catapult those especially good at rational arguing into positions of success and power.
²⁰
Maybe what’s really being favored is the ability to impress others, or even to bamboozle them. Machiavellian indeed.

Much attention has also focused on the ability to detect cheaters. For biologists, cheating means pretty much what it means for everyone else: failure to abide by the rules, in a way that gives
oneself a higher payoff than fairly entitled. Much social life involves exchanges, if not of actual items, then of attention, assistance, time and energy, and obtaining benefits as well as assuming costs and running risks. And sadly, in the process, there is a strong temptation to take more than one gives. It may be in the interest of a wolf, for example, to get a nice big chunk of moose meat, but at the same time, to hold back just a little when it comes to actually killing the moose, letting others take on the more risky duties. Achieving an optimal payoff almost certainly requires a degree of pro-social intelligence (to function adequately within the constraints and opportunities of a pack), along with Machiavellian intelligence, to deceive one’s pack mates when possible, as well as to detect the wiles of would-be deceivers and avoid being suckered by them.

When Shakespeare wrote in
As You Like It
that “the dullness of the fool is the whetstone of the wits,” this may be one of the very few cases in which his particular wit fell short—at least as devotees of the Machiavellian intelligence hypothesis see it: It is more likely that the sneaky, manipulative, high-grade intelligence of our smartest, most Machiavellian colleagues has been the whetstone of our own.

An especially important social exchange involves what is known as “reciprocal altruism,” essentially “you scratch my back, I’ll scratch yours.” It provides an important route whereby natural selection can favor apparent altruism, even between individuals who are not genetic relatives. I say “apparent altruism” because a true reciprocal exchange actually isn’t altruistic at all, since everyone ends up ahead: The initial beneficiary is helped, and then, when the situation calls for it, he or she repays the favor, so that the original back-scratcher gets its needs met, too.

The problem—and for many species and situations it is an insurmountable one—is that such exchange systems are vulnerable to cheaters, individuals who accept aid but then do not reciprocate. In fact, despite the fact that reciprocal altruism seems theoretically feasible, only rarely has it been clearly demonstrated in animals—presumably because of the ubiquitous temptation to cheat. Human beings are a notable exception: We are reciprocators par excellence, and it is at least possible—indeed, likely—that natural selection has favored a high level of intelligence in
Homo sapiens
as a way of countering the Machiavellian tendency to cheat, by endowing us with the ability to identify individuals and to hold them socially accountable. Just as selection could have favored a particular kind of Machiavellian intelligence that facilitates conniving and cheating, it could also have favored the additional intelligence needed to assess the trustworthiness of others and to hold them to a fair standard.

There are other aspects of social intelligence that might have been selected for among our ancestors, essentially as a complex, multifaceted response to the diverse challenges of social living, of which Machiavellian considerations are but one component. Anthropologist and evolutionary psychologist Robin Dunbar has made the argument that as group size increases, natural selection for greater intelligence—particularly, social intelligence—is likely to have intensified. In addition to the cleverness needed to compete and cooperate successfully in large social groups within which interactions are intense, increases in group size exert substantial pressure simply to keep the details and nuances of many different relationships in mind at the same time.

The issue is less fraught when social groups are essentially homogeneous, as we assume is the case with, for example, a school of herring. But when groups are highly structured and heterogeneous, with individuals recognizable as individuals, carrying with them the weight of their particular qualities as potential coalition members, competitors, mates, genetic relatives, etc., the payoff to an ability to retain and juggle these relationships—that is, to be socially intelligent—increases.