Games Primates Play: An Undercover Investigation of the Evolution and Economics of Human Relationships

by Dario Maestripieri

  PAIR-BONDING AND RAISING CHILDREN

  In other primates—including apes, the ones most similar to us—sexual attraction, sexual intercourse, and reproduction work pretty much the same way as they do in humans, but there is no bonding between the mother and the father of offspring. Take orangutans, for example. When the time comes for reproduction, the male and the female meet for the first time a few minutes before they have sex and then never see each other again. When the baby is born several months later, the mother raises the baby on her own. Orangutan and other primate babies raised by single moms do just fine. Some get sick and die, of course, but that has less to do with the father’s absence than with the baby’s overall health. Also, the father’s presence in these babies’ lives wouldn’t necessarily make them more successful as adults. Male orangutans, like many other primate males, impregnate females but don’t help at all with the kids. There are no bad feelings between males and females about this, but there are no good feelings either. There is no attachment, or bonding, or anything remotely resembling romantic love between mates.

  There are exceptions to this pattern. In a few primate species, the father’s help is either necessary for infant survival or can make the difference between a bad life and a good one. In small South American monkeys called tamarins, females give birth to twins but are not strong enough to carry both babies around all the time. If the father didn’t help with infant-carrying, the infants wouldn’t make it past the first week. To keep the father around and ensure his help with the kids, males and females form pair-bonds and stick together for most of their lives. The tamarins and the orangutans exemplify a simple rule that is generally valid not only among primates but among all vertebrate animals: whenever one parent alone is enough to raise offspring successfully, single parenting is the rule and males and females don’t form long-lasting pair-bonds.8 (In most mammals the single parent is the mother; in fish species it tends to be the father.) However, when offspring need both parents to survive and become successful adults, males and females form pair-bonds and raise offspring together. Most species of birds are pair-bonded because chicks must be fed in the nest, and one parent alone could not do the job.

  Psychologist Chris Fraley and two colleagues at the University of Illinois at Urbana-Champaign analyzed a large amount of scientific literature, first focusing on forty-four different taxonomic families of mammals and then on sixty-six species of primates, trying to reconstruct the evolutionary history of pair-bonding across time.9 In their analysis, a species was defined as pair-bonded if mates spent a lot of time together and if there were signs of mate guarding, extensive physical contact and proximity, and separation distress. It turned out that mammals that were considered pair-bonded also provided biparental care; in addition, these animals had longer life spans and the period of offspring development was longer and slower. The analysis focusing only on primates found exactly the same results: both pair-bonding and bi-parental care are rare in primates, but when they occur, they go hand in hand. In these species, offspring develop slowly and are particularly vulnerable and needy. Fraley and his colleagues concluded that pair-bonded and bi-parental care co-evolved in mammals, including primates, and that in species in which fathers began contributing to child-rearing, pair-bonding soon followed.

  Humans are no exception to the rule. If fathers did not cooperate with mothers in rearing children, children would lack important advantages they have when both parents help. Human fathers can provide help in important ways: they feed their children, protect them from danger, give them money, teach them all kinds of useful things, push them and support them, and get them out of trouble. There are two main reasons why humans are different from most other primates in the extent to which children need their fathers. One is that we have large brains, and the other is that we live in competitive and complex societies. Human brains are humongous by animal standards and take a long time to grow and mature. In fact, baby brains get so big during gestation that mothers must give birth before the brain has completed its growth; otherwise, the baby’s head wouldn’t fit through the birth canal. Brain development continues long after birth, and during this long, slow period of maturation human infants are vulnerable and need a lot of care. So a father’s help can make a big difference. A father’s help can also make a difference in ensuring that children become socially competent and successful adults. As I discussed in Chapter 2, because human societies are so competitive, young people need all the nepotistic support they can get to become successful adults. Even though single mothers can manage to raise their children and meet their basic needs, children who enjoy the additional support of their fathers have double the nepotistic connections to rely on (especially if they end up in the military or in academia).

  If male-female pair-bonds in animals and humans are about raising children together and not only about founding film production companies, as Brad and Jennifer did, and if love exists to cement this bond, then one might expect that love would fade and the bond dissolve if children are not conceived (building a nursery in the new house is not enough—you actually have to put a baby in it) or when the parents’ job is done and they want to move on with their lives.

  BREAKING THE BOND

  In the 1955 film The Seven Year Itch, a married man struggles with the temptation to leave his wife and small child to run off with the young woman next door, played by Marilyn Monroe. (This movie contains the famous scene in which Monroe stands on a subway grate and her dress is blown above her knees by a passing train.) The title of the film refers to the time in a marriage when—according to the U.S. Census Bureau—a divorce is most likely to happen. One possible explanation for this timing is that after seven years of marriage many couples have successfully raised one or two children through the risky infancy years and can catch their breath and realize they don’t want to be around each other anymore, or else they haven’t had children at all and decide it’s time to look for another potential mate. Brad Pitt and Jennifer Aniston divorced after having spent seven childless years together, so the timing of Brad’s itch is consistent with this theory. Or perhaps when Marilyn Monroe or Angelina Jolie enter the picture all bets are off and, kids or no kids, married men (including presidents of the United States) start itching and getting ideas in their heads. I can cite some research in support of the first theory; support for the second theory can be found in Marilyn’s and Angelina’s biographies.

  To understand the first theory, it is important to know that the risk of infant mortality in humans and other primates is very high in early infancy and decreases steadily as infants grow older. Thus, if a couple splits up shortly after a baby is born, the baby’s survival or well-being could be at risk. Anthropological study of indigenous cultures supports the notion that in the first few years of life human children need all the help they can get. Breast-feeding is generally known to reduce the baby’s risk of catching diseases because the mother transfers her immune defenses against germs to the baby through her milk. In contemporary hunter-gatherer populations such as the !Kung in South Africa, mothers breast-feed their babies for approximately four years. Emory University anthropologist Melvin Konner, who studied the !Kung in the 1970s, has suggested that four years was probably the average interbirth interval for humans during much of our evolutionary history.10 Among the hunter-gatherers, a baby is fully weaned at four years old: at this age, the transition from breast milk to solid food is complete. The risk of infant mortality then drops even further. At this point, the mother typically has another child. But not all couples proceed to have a second child.

  In the late 1980s, anthropologist Helen Fisher, author of the 2004 book Why We Love: The Nature and Chemistry of Romantic Love, gathered divorce data from fifty-eight different human societies around the globe from the records of the Demographic Yearbooks of the United Nations.11 She discovered that when married couples divorce, they tend to do it around the fourth year of their marriage, typically after having had a single child. One interpretati
on of this discovery is that many human couples stay together at least the minimum amount of time necessary to successfully raise one child together. Fisher took this idea a step further, however, and speculated that humans might have a predisposition to be serial monogamists. Although “serial monogamist” sounds a lot like “serial killer,” it simply means that people are socially bonded to one partner at a time, but don’t stick to the same partner their whole life; they go from one partner to another, in succession. According to Fisher, humans are likely to switch partners every four years, after having a child. In reality, there is no strong evidence that humans are serial monogamists. Although the number of divorces keeps increasing in many societies around the world, there are many couples who remain married forever, raise children together, and aren’t convinced that their parenting job is done even when it’s pretty clear that their children can make it on their own. My own parents have been married for over fifty years, and my mother still insists on buying me socks and underwear. Clearly, she doesn’t think her job is done.

  When divorce does occur, the interval between marriage and divorce varies widely across societies and historical periods. A 2010 study of marriages and divorces in Italy conducted by ISTAT, a research group that conducts statistical analyses of demographic data, found that Italian marriages last, on average, fifteen years.12 The average age at which men get divorced is forty-five, and for women it’s forty-one. Italians now marry relatively late, in their mid and late thirties, so divorce tends to occur when couples have either been married for several years and produced no children or when they have had one or two children and the youngest is four to five years old. Again, this is consistent with the theory that humans form pair-bonds in order to have and raise children.

  Common sense suggests that when married couples divorce, there either wasn’t much love to begin with or love was strong at the beginning but then gradually weakened. The latter possibility is consistent with another theory of love, developed by a friend of mine and related to me after a few drinks, according to which love is just a stage in a relationship—an early stage. My friend’s theory is actually quite compatible with the theory about pair-bonding and child-rearing. Unlike Robert Frank’s commitment theory, according to which love between two partners should grow stronger over time, as the risk of defection increases, the “early stage” theory and the “pair-bonding and child-rearing” theory both maintain that love must be strong at the beginning of a relationship and last at least a few years, but doesn’t necessarily need to remain so forever.

  But if humans form pair-bonds to jointly raise their children the way birds and other animals do, why is it that romantic love occurs only in our species? Cooperation between mothers and fathers poses the commitment problem, and Frank suggests that romantic love evolved to solve this problem. Is cooperation in rearing human offspring in some way different from other forms of animal or human cooperation such that it presents unique problems requiring unique solutions? I don’t think so. As a cooperative partnership, the human pair-bond is not qualitatively different from other long-term cooperative relationships. In many species of animals, pairs of individuals cooperate in finding food, keeping each other clean, or supporting each other in fights against other individuals. Humans cooperate with other humans in a million different contexts. All of these cooperative relationships pose the commitment problem, yet the problem is not solved with romantic love. As we’ll see in the next chapter, commitment problems are not addressed with irrational feelings but with repeated testing of the bond.

  Love is an emotion, so to understand its evolutionary function we have to place it in the broader context of the evolutionary function of emotions. Although emotions occur in the context of social relationships, they also occur in many other nonsocial contexts.

  Love the Energizer

  When one person joins another

  It creates a chain reaction, which leads to fission

  The release of energy culminating in a vast explosion

  Whose result is total devastation

  The wiping away of cities

  The crumbling of continents

  The destruction of mountain ranges

  The melting of glaciers

  The boiling away of oceans

  The cracking of a planet

  The collapse of a solar system

  A galaxy folded in upon itself

  The universe, gone

  Just because two people get involved.

  —Joe Frank, “Love Prisoner”

  monologue from his radio show The Other Side

  One major function of emotions is to energize motivation. If we experience a strong positive or negative emotion, we become motivated to do something that’s beneficial or to avoid something that’s harmful. Pain exists to make sure organisms do everything they can to avoid things that can damage their bodies. If you are crazy enough to stick your finger in the flame on the kitchen stove, pain is there to protect your body and make it difficult for you to hurt yourself, no matter how crazy you are. Sexual desire and orgasm exist to make sure organisms are highly motivated to engage in sexual intercourse and produce children, regardless of their opinions on the subject. Sexual urges are so powerful that it is difficult even for priests who take a vow of celibacy to completely suppress their sexuality. Their emotions work against their conscious decisions, and the result is that some of them end up in the news for engaging in inappropriate sexual behavior. People make arbitrary decisions about all kinds of things, but matters of survival and reproduction are too important to be entirely dependent on people’s conscious decisions. Emotions evolved to encourage us to do what’s good for us regardless of what we think about it. Romantic love evolved, I argue, to motivate men and women to form pair-bonds.

  But why the need for this extra emotional energizer? I think the answer has to do with our primate evolutionary past. In birds pair-bonding is an ancient adaptation. Birds have probably been pair-bonded organisms for many millions of years. This means that natural selection has had plenty of time to sculpt birds’ brains and provide the necessary wiring to support the psychological and behavioral adaptations for pair-bonding. In comparison to birds, human pair-bonding is an evolutionary novelty. It arose very recently—a few million years is equivalent to the day before yesterday on the evolutionary time scale—and very quickly in response to the rapid changes in brain size and patterns of child development that made bi-parental care necessary or advantageous. To complicate things, humans probably evolved from a chimpanzee-like ape species whose members were sexually promiscuous, whose males did not contribute anything at all to child-rearing, and in which there were high levels of conflict between the sexes (such as male aggression toward females and sexual coercion). The brains of our ape ancestors had probably been shaped by sexual selection for millions and millions of years to support mating and reproductive strategies that did not involve pair-bonding. As psychologist Paul Eastwick argued recently, when the circumstances became favorable for the evolution of pair-bonding in the human lineage, natural selection had to quickly modify human brains in ways that would counteract other features that had been honed through eons of sexual selection.13 It wasn’t an easy evolutionary step for the male brain of a sexually promiscuous, aggressive, and misogynistic chimpanzee-like ape to become the socially monogamous, female-loving, and paternal brain of a human being. The need for this rapid transformation presented a special evolutionary problem, which required a special solution. This special solution was romantic love and adult attachment.

  But how did natural selection find this special solution? How did it come up with romantic love?

  The History of Love

  Being often at the airport, I cannot help but notice how people behave when they say good-bye to their loved ones. I have seen many a husband hold his wife’s hand while she is getting her boarding pass at check-in and carry her baggage until she gets past the security line; finally, before they separate, they smile, hug, and kiss each ot
her. I have also seen tears in both partners’ eyes and other painful expressions when they finally have to let go of each other’s arms. I am clearly not the first or the only behavioral scientist who has observed these scenes and wondered about the nature of love. Psychologists Chris Fraley and Phil Shaver conducted a study of this phenomenon, which was published in 1998 in the Journal of Personality and Social Psychology with the title “Airport Separations: A Naturalistic Study of Adult Attachment Dynamics in Separating Couples.”14 They conducted this study because they thought that the way romantic partners behave during airport separations might shed light on the nature and origins of human love.

  Fraley and Shaver had a team of four observers who took written notes on the behavior of separating couples at a small metropolitan airport. For comparison purposes, the four observers also recorded the behavior of couples who were flying together. These are some of the behaviors they observed in the separating couples:

  They held hands.

  They hugged and held each other for about five minutes.

  He kissed her several times when she tried to leave.

  They gave each other a long and intimate kiss.

  He massaged her inner thigh.

  They both cried and wiped the other’s tears away.

  She, in a comforting manner, stroked his face.

  He walked away quickly; she walked away crying.

  She whispered, “I love you,” to him as she boarded.

  They continued to hold hands even though they were walking away from each other.