At departure, she was the last to board the plane.
After he left, she went back to the window and watched the plane leave.
She was still at the window twenty minutes after the plane left.
In one case, a man who had already boarded the plane came rushing out for one last kiss, unleashing the wrath of the flight attendants, who urged him to return to his seat immediately.
In addition to observing and recording the behavior of these separating couples, the researchers also asked them to fill out questionnaires about their personality, the length of their relationship, and the degree of subjective distress they experienced during separation from their partner. The main goal of this study was to show that separating couples engage in behaviors functionally similar to those observed in children who are being separated from their parents. In both cases, there are behaviors that function to seek or maintain contact or proximity, expressions of sadness or distress, caregiving and comforting behaviors, and sometimes aloofness and rejection of affection. The general theory inspiring this study, which also guides much of contemporary research on romantic love, is that love and adult attachment have their evolutionary origins in the emotional and social bond between a child and its caregiver. The bases for this theory were laid out about fifty years ago.
In the early 1960s, British psychiatrist John Bowlby developed a theory to explain why young children are strongly bonded to their primary caregiver, usually their mother. According to Bowlby’s “attachment” theory, young children have a biological predisposition to become emotionally attached to a caregiver, which manifests itself as behaviors aimed at maintaining proximity or stimulating interaction, such as crying, smiling, following, and clinging. Human infants are totally dependent on their caregivers for protection from the environment. Bowlby argued that the attachment system probably evolved by natural selection as a set of psychological and behavioral adaptations that promote infant survival by enhancing infant proximity and interaction with a caregiver. Bowlby got his ideas about attachment from observing children’s reactions to separations from their parents before being checked into a hospital, as well as from reading descriptions of mother-infant interactions in monkeys. It turns out, in fact, that the infant attachment system is not unique to the human species but exists in many species of monkeys and apes that are closely related to humans. It’s at least 35 million years old—a lot older than human pair-bonding.15
Bowlby argued that the infant attachment system has a set goal—the maintenance of contact with or proximity to the mother—and specific activating and terminating conditions. The attachment system is activated when the infant is separated from the mother, and it’s terminated when contact or proximity is achieved. The system thus works like a thermostat that measures the current temperature and after comparing it with a preset standard, makes adjustments. The infant attachment system has three defining features: young children show anxiety and fear of strangers when separated from their mother (they cry, cling, and become anxious or sad); they run back to their mothers when they are scared (using her as a “safe haven”); and when they are calm and confident they use their mother as a “secure base” for exploration, walking away from her to explore and play but often checking back with her to make sure everything is okay.
Although infants cry from the moment they are born, the main defining features of the attachment system, such as separation anxiety and fear of strangers, first appear when children are between six and nine months old. The attachment system continues to operate through the rest of childhood and even into adolescence, although the behaviors through which attachment is expressed may change. The basic features of the attachment system can be seen in all children, although not all children react the same way to a short separation from and subsequent reunion with their mother; some children are more comfortable being separated and are loving and affectionate at the reunion, whereas others get very anxious during separation and express anger and rejection toward the mother at the reunion. It turns out that both the basic features of infant attachment and the differences among children can be observed not only in all human societies and cultures around the globe, but also in the species of monkeys and apes that are most closely related to us: rhesus monkeys, baboons, and, of course, chimpanzees and the other great apes.
Freud was among the first to write about the striking similarities in the physical intimacy that typifies lovers and mother-infant pairs, including the way romantic partners use baby talk with each other. Fraley and Shaver’s airport study and many others conducted since the late 1980s have shown that the features that characterize the infant attachment system—proximity maintenance, separation distress, safe haven, and secure base—can also be observed in romantic relationships between adults.16 Moreover, children who were securely attached to their mothers turn into adults who are comfortable and laid back in romantic relationships, whereas children who were insecure, anxious, and ambivalent/angry toward their mothers (or fathers), well, they behave the same way toward their romantic partners in adulthood. Finally, there are also many similarities in the temporal development and transformation of attachment relationships in mother-child pairs and romantic partners. Romantic attachments are usually more mutual and symmetrical than child-mother attachments. In addition, in romantic relationships partners often alternate in the roles of the immature individual who needs attention, comfort, and reassurance and the caregiver who provides all these things.
Given all of these theories and observations of the last fifty years, I suggest that the evolutionary history of human romantic love may have progressed along the following lines. As human brains grew and infants became needier and more vulnerable for a longer period of development, such that the father’s involvement and bi-parental care became necessary, natural selection had to come up with a way to motivate men and women to stay together for as long as it took to raise a child successfully. Now, natural selection never invents anything from scratch but rather modifies and rearranges preexisting structures. The psychological and emotional adaptations for the infant attachment system already existed in the brains of our ape ancestors and had worked pretty well to keep infants and mothers together. Natural selection tweaked this system, making it operational through adulthood, so that it could be used to bond mates to each other. Some of the neural circuits and the neurochemical substances that had been used to bond mothers and children, such as those involving oxytocin and endogenous opioids (which are also involved in regulating the body’s responses to stress and physical pain), also became involved in mediating bonding between adults.
To accomplish the goal of fostering long-lasting emotional and social bonds between adult males and females, natural selection tinkered not only with the brains of our ape ancestors but with their bodies as well. The bodies of our ape ancestors were probably similar to the bodies of modern chimpanzees: well adapted for intense sexual competition and sexual conflict, but not for pair-bonding. For example, males were larger and stronger than females, had larger and sharper canine teeth, and had relatively small penises but huge testicles that produced large quantities of testosterone and sperm. Females, for their part, advertised their fertility period during their menstrual cycle through large sexual swellings to incite sexual competition among males. To foster pair-bonding and cooperative relationships between the sexes, natural selection reduced the differences in body size, strength, and weaponry between males and females. Then it eliminated obvious signs of ovulation in women and increased their receptivity throughout their menstrual cycle. This provided the opportunity for paired men and women to have sex all the time, thus reinforcing their union and increasing the man’s confidence that when a child was born it was really his, which in turn increased his willingness to provide paternal care. At the same time, natural selection reduced paired men’s desire for sexual variety and promiscuity by reducing their testis size and lowering their testosterone levels. Human males have relatively small testicles for their body siz
e and produce small amounts of sperm and testosterone compared to male chimpanzees. I once saw a slide of a researcher holding a chimpanzee brain in one hand and a testicle in the other; they were approximately the same size, and not because chimpanzee brains are small.
Another physiological adaptation for pair-bonding in human males is the dramatic reduction in their production of testosterone when they find themselves in committed relationships or are married with children.17 Lower testosterone in romantically committed men curbs their desire for other women and allows them to concentrate on their wives and children. This has been shown by many studies, including one that my colleagues and I conducted at the University of Chicago involving over five hundred MBA students. Finally, various researchers, including psychologists Cindy Hazan and Debra Zeifman, have suggested that the exceptional length of the erect human penis—human males have by far the longest penis in relation to their body size of all the primates—is also an adaptation for pair-bonding.18 The long penis makes possible a wide variety of copulatory positions, including more intimate face-to-face, mutually ventral positions, which promotes social bonding during sexual intercourse. Ventro-ventral sexual intercourse is rare in primates but common in another species closely related to us, the pygmy chimpanzee, or bonobo; like humans, bonobos use sex for social bonding purposes. The long human penis may also increase the probability of female orgasm, which heightens the female’s readiness for engaging in sexual activity, thereby strengthening the bond with her mate.
The multiple physical, physiological, and psychological adaptations that have arisen through natural selection to induce human males and females to form pair-bonds and cooperate in rearing offspring generally work very well. The most amazing psychological adaptation for pair-bonding—romantic love—creates in the human mind a longing for the desired partner and a psychological dependence not dissimilar from that existing between a young child and her mother. Successful bonds involve a profound psychological and physiological interdependence between partners such that the absence or loss of one partner can be literally life-threatening for the other. Conversely, solid and stable romantic relationships can have many positive effects on the health and longevity of both partners and their children. Although economics can help us understand some aspects of pair-bond formation and some of the issues involved in cooperation between partners, evolutionary biology tells us that human romantic pair-bonds are far more than business partnerships based on the principles of cooperation and reciprocal altruism.
So back to the original question: Why did Jennifer Aniston and Brad Pitt first fall in love with each other only to break up? Can the theories from economics and evolutionary biology discussed in this chapter explain why some Hollywood celebrities (as well as us common mortals) form pair-bonds and then split up?
Well, read the following quotes from the August 30, 2010, issue of US Weekly and judge for yourself:
Actor Neil Patrick Harris [the famous TV child doctor Doogie Howser] and his partner David Burtka are expecting twins via a surrogate mother. A source close to the couple reveals: “They bonded about wanting kids and having a family from the very beginning, which is why they fell in love. It’s a dream come true.”
Actress Halle Berry, speaking about former partner Gabriel Aubry, with whom she has daughter Nahla, 2: “You realize you are not meant to go the distance with everybody. We were meant to bring this amazing little person into the world . . . and we are a family until we are not here anymore.”
Chapter 7
Testing the Bond
The Baboon Solution to the Commitment Problem
Male baboons form cooperative relationships with each other that involve aggressive alliances and mutual support in fights. Like the business and romantic partners in the previous chapter, male baboons, too, face the commitment problem: one of the two partners might cheat and double-cross the other, or simply end their relationship, leaving the other in the dust. So they’ve come up with an unusual way to deal with the commitment problem: they fondle each other’s testicles.
Other primates are also known to engage in similar practices. In ancient Rome, two men taking an oath of allegiance held each other’s testicles; men held their own testicles as a sign of truthfulness while bearing witness in a public forum (hence the word “testify”1). The behavior of male baboons and ancient Romans can be explained by the Handicap Principle (HP), a biological theory according to which the most effective way to obtain reliable information about a partner’s commitment in a relationship—whether a friendship, a romantic relationship, or a business partnership—is to impose a cost on the partner and assess the partner’s willingness to pay it. But before I say anything more about this, let’s go back to the strange habits of male baboons.
Adult male baboons are aggressive and dangerous animals. Despite their relatively small size—approximately that of a German shepherd—male baboons are strong and fast, with large, sharp canine teeth that make their bites potentially deadly. They are also fearless and won’t hesitate to attack animals much larger than themselves, such as lions and chimpanzees. But what makes male baboons so dangerous is that when they attack they are rarely alone; they do so in pairs or small gangs of three or four males. Although male baboons cooperatively hunt smaller animals when they feel like eating meat for dinner and also cooperatively attack large predators that prey on baboons, both of these reasons for cooperating are relatively rare. When male baboons form aggressive alliances, most of the time they do it to fight other male baboons.
Baboon society is a competitive environment. Adult males compete with each other to mate with females and to acquire and maintain high-ranking positions in the dominance hierarchy. Baboons are highly promiscuous monkeys—males like to mate with many females, and often. Male baboons have large testicles for their body size and can ejaculate ten to fifteen times a day, or more. High-ranking males, however, monopolize fertile females and won’t let lower-ranking males come near them. The 1977 study by Craig Packer that I mentioned in Chapter 2 showed that male baboons have figured out a way to circumvent the monopolization of fertile females by high-ranking males.2 Two males will work in tandem: while one of them picks a fight with the high-ranking male who is guarding the female, the other one takes advantage of the diversion to mate with her. A few days later they play the same game but with reversed roles: the guy who got lucky with the female will return the favor to his buddy and pick a fight to create the diversion. Since fighting to help another individual mate is an altruistic act, Packer’s study has become a classic example of reciprocal altruism in primates. Adult male baboons also form coalitions when they fight for power, just like the male macaques discussed in Chapter 4, but even more so. To rise in rank, two or three adult males may gang up against a higher-ranking male, defeat him in battle, and make him lose his status or kick him out of the group altogether.
Whether male-male coalitions are formed to gain sex or power, they are not formed instantly or randomly. Just as the formation of human political alliances requires a lot of networking, baboons will take a long time to get to know each other, form a social bond, and develop a certain degree of trust before they form an alliance. The social bonding between coalition partners entails hanging out together and exchanging a lot of grooming. If adequately maintained, cooperative relationships between two males can last a long time and result in many coalitions.
But just as there is competition in mating and dominance, there is also competition for good political allies, and high-ranking males are sought-after coalition partners. This competition makes cooperative relationships between males unstable, capable of ending at any time, and ripe for betrayal: even the male baboon that you thought was your best friend could, in the middle of a fight, decide to switch allegiances and side with your worst enemy. Male baboons cannot sign a written agreement to cooperate, much less enforce the contract with the threat of financial sanctions. Nor can baboons talk, so a male baboon must figure out in some other way whether his friend
ship with another baboon is strong or weak and whether the other party can be trusted as a coalition partner.
Now imagine this scene. Forty to fifty baboons are sitting around and enjoying the breeze on a sunny summer afternoon. Some monkeys are looking for food on the ground, while others are grooming or sleeping. Clint Eastwood and Eddie Murphy are two adult males who occupy high-ranking positions in the group and are quite successful with the ladies. Each has a small harem of three or four females, with whom they mate all the time and who are loyal to them. Other males in the group are lucky to have one female who pays attention to them, and some old guys have been out of the mating business for a while. (In this particular species of West African baboons—the Guinea baboon—males keep small harems of females, a bit like the hamadryas baboons that live in East Africa.) Clint and Eddie are sitting twenty yards apart, each minding his own business. Out of the blue, each glances at the other over his shoulder and makes eye-to-eye contact. In that split second, their baboon minds decide that it’s time for some bond-testing.
Clint and Eddie run toward each other, meeting approximately halfway. As they run, Clint makes a funny facial expression, his eyes half-closed and his ears flattened back against his skull, while Eddie smacks his lips very rapidly. When they meet, each baboon lifts his leg—the way a male dog does to pee—and the other briefly holds his testicles in his hand. Without even looking at each other, they run back to where they were before, sit down, and continue with their business as if nothing had happened. The whole interaction lasts mere seconds and happens spontaneously: nothing has led to it, and nothing follows. The other baboons in the group hardly notice—they’ve seen this scene a million times before.
My former PhD student Jessica Whitham saw hundreds of these interactions (and captured some good ones on video) when she observed the group of Guinea baboons at the Brookfield Zoo in Chicago to collect data for her master’s thesis.3 (Incidentally, she is the one responsible for naming the baboons after Hollywood celebrities.) Although homosexual behavior is not uncommon in monkeys and apes—both males and females mount individuals of the same sex under various circumstances—the fondling of genitalia performed by male baboons has nothing to do with sex. It’s a social ritual that primatologists call a “greeting.” In her thesis, Jessica showed that pairs of adult males who have stable cooperative relationships—characterized by frequent grooming and alliances—often exchange greetings, while males with poor or unstable relationships either don’t exchange greetings at all or initiate greetings but are unable to complete them.
Games Primates Play: An Undercover Investigation of the Evolution and Economics of Human Relationships Page 20