So why haven’t chimpanzees been selected to develop the same sort of mind-reading skills that pay off in more efficient learning among humans? If mind-reading human mothers respond more flexibly to infant needs and are better equipped to rear and tutor offspring, why haven’t other apes spent 6 million years evolving and refining their intersubjective aptitudes? A lovely hypothesis for mind reading still leaves us grappling with the question: Why us and not them? The next hypothesis, currently the most widely cited of the alternative explanations for mind reading, suffers from the same limitation.
(Top) A child growing up in a gathering and hunting society watches attentively as his mother cracks mongongo nuts, a staple food among the !Kung. Learning just how to strike the extremely hard shells is a skill that can take years to master. (Bottom) During some seasons, chimpanzees as well spend hours cracking open the hard outer shells of palm oil and coula nuts by hammering them against a stone “anvil.” Like their modern human counterparts, chimpanzee mothers patiently model how to hold the stone “hammer” or position a nut on the anvil, even allowing a grabby little apprentice to take tools or nuts right out of their hands. Although chimpanzee mothers do not actively teach, they remain sensitive to their infants’ struggles. In the best pedagogical tradition, mothers may even allow a frustrated apprentice to take some of her own already extracted nut meats, a well-timed and encouraging reward. (Top: I. DeVore/AnthroPhoto. Bottom: © Tetsuro Matsuzawa)
THE MACHIAVELLIAN INTELLIGENCE HYPOTHESIS
The craftiness of a subordinate chimpanzee able to take advantage of inside information about what another chimpanzee knows is often explained with reference to Machiavellian intelligence. The hypothesis derives its name from Niccolò Machiavelli, whose advice to a sixteenth-century Italian prince has become associated with ruthless political manipulation (much as Karl Rove’s advice did for a recent generation of American politicians). Most thoroughly developed by Andrew Whiten and Richard Byrne at St. Andrews University in Scotland, the Machiavellian intelligence hypothesis posits a 70-million-year legacy of extreme sociality combined with a universal primate urge to strive for status.
Higher primates possess a general social intelligence that equips them to differentiate probable kin from nonkin, assess the strengths and weaknesses of different individuals, keep track of past social interactions in order to predict who is currently dominant to whom or who is likely to reciprocate and who will not.36 To cope with social complexity, monkeys and apes alike have to be what the primatologist Alexander Harcourt terms “consummate social tacticians.”37 Baboons, rhesus monkeys, and chimpanzees all keep track of the intricate and fluctuating status of other group members so as to select and maintain advantageous allies when competing with their fellows. Apes are if anything even more sophisticated than monkeys at gauging status fluctuations and assessing competitive intentions, combining typically primate social intelligence with a rudimentary theory of mind.38
Together with its corollary, the social intelligence hypothesis, the Machiavellian intelligence hypothesis has become the explanation of choice for why some higher primates excel at problem-solving tests involving what others can see or know—the better to manipulate or deceive them—and for why they have larger brains for their body size than do other mammals.39 Indisputably, Machiavellian intelligence does a fine job of accounting for why a chimpanzee subordinate might disguise the fact that he has located some preferred food, enabling him to circle back later and enjoy the fruits of his deception once the dominant animal is out of the way.40 The same Machiavellian intelligence that renders primates adept at forging complex political alliances and deceiving others may also have helped chimpanzees coordinate joint activities like hunting. A band of males will fan out so that one or more males block any escape route that their prey, say a colobus monkey, might take. Then one of the males climbs up after the targeted prey. Even though it’s not clear just how conscious or actually coordinated this behavior is, the hunters act as if they know what other animals will do and anticipate what the consequences are likely to be. Their actions have the earmarks of what we would call planning.41
Just as the need for empathizing and responding to the needs of vulnerable young helps to explain the development of specific areas in mammalian brains, so too the need for greater Machiavellian intelligence can help to explain the expansion of the neocortex. These planning portions of the brain were useful in assisting the common ancestors of humans and other apes to predict what others would do in competitive or predatory contexts.42 But here’s the problem. We still have to explain why humans are so much better than chimpanzees at conceptualizing what others are thinking, why we are born innately eager to interpret their motives, feelings, and intentions as well as to care about their affective states and moods—in short, why humans are so well equipped for mutual understanding.43 Chimpanzees, after all, are at least as socially competitive as humans are. Attacks from conspecifics (both infanticide and deaths due to lethal raids by bands of males from neighboring groups) are major sources of mortality.44 Male and female chimpanzees are even less abashed about striving for dominance status than men and women are.
And like humans, chimpanzees have a lust for meat, and they cooperate in rudimentary ways when hunting or making raids on other groups. Surely, chimpanzees would benefit from being able to outwit quarry or psych out competitors every bit as much as our ancestors did. So why didn’t selection favor even greater and more Machiavellian intelligence in Pan troglodytes? If social intelligence evolved to help individuals wipe out their neighbors, surely chimpanzees needed it as much, or more, than humans did.
Such questions are so obvious that some readers are probably wondering why no one asked them before. The main reason is that we were laboring under a wrong starting assumption about the capacities of social cognition in the common ancestor of humans and other apes. Most, perhaps all, researchers assumed that the ability of newborns to seek out faces, fixate on them (on eyes especially), gaze deeply into those eyes, and process information about the expressions observed there were uniquely human and acquired after our hominin ancestors split off from the long-ago common ancestor of humans and other apes. Because we took for granted that human infants’ capacity for interpreting and imitating faces was unique, we presumed that it was a recent human acquisition absent in other apes.45 Certainly scientists were aware of selection pressures favoring Machiavellian intelligence in other apes, but we assumed that nonhuman apes lacked the neural underpinnings to seek out, read, and imitate others’ facial expressions—initial steps toward mind reading.
Mistakenly, we thought baby chimpanzees did not look into or imitate faces the way human babies did. As long as we assumed that only human newborns possessed the basic neural apparatus for assessing conspecific facial expressions, empathizing with what others were experiencing, and thereby reading their intentions, there seemed little need to ask why other apes never evolved better capacities for mind attribution. We simply took for granted that they lacked the basic equipment. All this started to change around the beginning of the twenty-first century, when revolutionary discoveries about what other apes are actually capable of forced reconsideration of the question of why humans are so much more inclined than other apes toward intersubjective engagement.
MONKEY SEE, MONKEY FEELS WHAT IT WOULD BE LIKE TO DO
In 1996 an Italian neuroscientist who was part of a team carrying out routine studies on how particular motor skills are reflected in brain activity noticed something odd. The neurons that fired when a macaque grabbed a raisin also fired when the monkey simply watched the researcher pick up and eat a raisin.46 Neuroscientists quickly christened this new class of brain structures “mirror neurons” because the same areas of the brain that would be activated by doing something are also activated just by watching someone else do the same thing. The serendipitous discovery of mirror neurons led to an explosion of speculation and new research into “the neural underpinnings of embodied simulation” to learn ho
w the brain reacts when we watch someone else do something.
Researchers hypothesize that mirror neurons allow creatures to vicariously experience what another individual is doing. By mentally going through the same motions, the mimic gains a better understanding of what the actor being copied is intending to do.47 Thus, the discovery of mirror neurons generated enormous excitement among developmental psychologists and clinical psychologists as well as among neuroscientists. From the outset, researchers suspected that mirror neurons play a role in empathy as well as imitation. This was consistent with at least one theoretical model for how human infants first learn that other individuals have mental states and minds of their own. In this model, the developmental psychologist Andrew Meltzoff sought to integrate what neuroscientists were learning about neural structures with older theories about how babies observe, imitate, and learn.
Years before, Meltzoff together with Keith Moore reported that some human babies as young as 12 hours old possess the innate ability to imitate others. Hard as it was to believe when first reported back in 1977, and in spite of continuing debate over whether the responses by very young babies are actually imitation, indisputably some babies exhibited a complex responsiveness to others much earlier than previously assumed. Meltzoff’s findings have been replicated in more than 13 different labs, not to mention in the homes of curious parents who can’t resist making funny faces at their babies. My own babies are grown, but Meltzoff’s tongue protrusion test remains one of my favorite ways to while away time at airports. Caught in the right mood, a baby will often respond to tongue protrusions by sticking out her tongue. After repeating his experiments with even younger newborns, Meltzoff quipped, “You can’t get much younger than 42 minutes old.” Meltzoff was convinced that he had documented that “a primitive capacity to imitate is part of the normal child’s biological endowment.”48
It has been known for a long time that humans, including babies, are fascinated by faces. Today we realize that a special region of the brain and special cells register and process information about faces.49 Right from birth, human babies seek out any nearby face, and when they encounter their mother’s face, they may gaze deep into her eyes as she returns their gaze. In an inspired set of experiments, Meltzoff demonstrated that some of these very new babies were not just looking for faces but seeking to engage and perhaps also identify with them. To Meltzoff, early imitation implies that “seeing others as like me is our birthright.”50
Like many readers of Science magazine back in 1977, I was astounded by two juxtaposed strips of photos. In the strip on top, a young and goofy-looking Meltzoff was photographed sticking out his tongue, opening his mouth, and pursing his lips. Just below, with eyes fixated on Meltzoff’s face, an alert newborn performed an approximation of each expression. (Meltzoff and Moore 1977:75)
When Meltzoff’s observations were originally made, most of us still took for granted that mutual gazing along with this early capacity of newborn babies to imitate what they saw was uniquely human as well as universal. This was consistent with the limited evidence we then had for other apes. Hypothesizing that a baby who first observed and then imitated someone else was mentally making an analogy between himself and that someone else, Meltzoff proposed “that infants’ connection to others emerges from the fact that the bodily movement patterns they see others perform are coded as like the ones they themselves perform.”51 Once memories of such experiences are stored away, they become the basis for future assessments about both self and others, and the relationship between them. In Meltzoff’s words: “Empathy and role-taking and all manner of putting yourself in someone else’s shoes emotionally and cognitively seem to rest on the connection between self and other.”
Babies everywhere are fascinated by faces. Here a Himba mother in Namibia gazes into the face of her three-to-four-month-old baby, first making eye contact, then kissing him on the lips. Seconds later, the mother scrunched up her face to copy the baby’s snorts and smiles as she touched him with her nose. The fascinated baby smiled back with flashing eyebrows and little snorts, occasionally sticking his tongue out. Even after the mother became distracted by conversation with other people, the pair would occasionally resume their mutual gaze. (Video by I. Eibl-Eibesfeldt/Human Ethology Archives, with summary of image context by Niko Larsen)
As soon as mirror neurons were discovered, Meltzoff began to wonder if they might help explain the unusually well-developed abilities for making connections with and imitating others that he had documented in human infants. He hypothesized that “the neuro-cognitive machinery of imitation lies at the origins of empathy and developing a theory of mind.”52 Combine mirror neurons with mutual gazing and imitation, and, for Meltzoff, mind reading follows. Convinced that he was on the right track, Meltzoff lapsed into poetic metaphor: “Through understanding the acts of others, we come to know their souls.”53 The mention of souls leaves little doubt that developmental psychologists at the beginning of the twenty-first century still assumed they were dealing with exclusively human capacities. Eyes, long celebrated by poets as “windows” into the human soul, played a big role in such assumptions. But what is distinctive about human eyes that allows this unique depth of insight?
THE EYES HAVE IT
Post a photograph of two staring eyes above the coffeemaker in an office lounge and you are likely to discover—as a team of British psychologists did in 2006—that people pouring themselves a cup will be more likely to deposit the recommended payment (in that instance, fifty pence).54 Humans are not unusual in this respect. From time immemorial, staring eyes possessed this special salience. Vertebrates with brains no bigger than an iguana’s or a wild turkey’s can sense if someone is looking at them. I can personally vouch for this after trying to sneak up on the wild turkeys at our farm in northern California. Somehow, they always know how to stay just out of view, not necessarily farther away, but just below some obscuring ridge so I cannot see them. Like many animals, Old World monkeys and apes find it unnerving to be stared at (though, curiously, this is not true for New World monkeys such as marmosets or tamarins).55
Like other apes, humans also perceive direct stares as threatening. But meanings conveyed by long looks can also be quite variable. Human eyes convey extra information about what an individual is feeling, looking at, and intending. True, other apes also focus, squint, and blink, and their eyes register patterns involving light and color the same way human eyes do. Other primates like baboons call attention to their eyes by lowering pale lids and “flashing” their brows upward in arches of great significance much like humans do. But humans communicate with their eyes more; many humans emphasize the direction of their gaze with a conspicuous white surround highlighting exactly where the pupils are pointed.56 The direction of such people’s gaze is thus easier to read than it is in other apes, whose gaze direction is obscured by a dark surrounding matrix. Only a sliver of white is ever—and then only occasionally—visible when an orangutan or chimpanzee glances sideways.
It is this ratio of white to dark that magnifies intensity and lends emotional meaning to facial expressions, generating the psychological response to eyes that are open wide in fear or surprise.57 It is the flash of white that jolts our amygdalae when we notice another person startle. It would be pointless for a marauding chimpanzee on patrol (even assuming that a chimp could talk or carry a gun) to tell his comrades, John Wayne–style, “Don’t shoot ’til you see the whites of their eyes.” No matter how close the enemy came, defenders would be unlikely ever to see any whites of eyes unless their enemies were human beings. This difference suggests that eyes capable of communicating information about intentions may have evolved in collaborative rather than competitive contexts. Information thus conveyed was beneficial to the signaler as well as the receiver.58
Such differences are one reason why it was taken for granted that humans were the only apes that engaged in mutual gazing, imitated facial expressions, and used eyes to attribute mental states to others. This view
fit with Meltzoff’s ideas about the importance of imitation in empathy. Our supposed uniqueness in these respects was also consistent with Tomasello’s proposal that “human beings, and only human beings, are biologically adapted for participating in collaborative activities involving shared goals and socially coordinated action plans.” It followed that human babies would be born with special physical attributes and aptitudes for reading mental states and intentions, and communicating their own. What a lovely conceptual package—as long as it lasted. If only other apes would stick to their side of the Rubicon!
Over the past decade or so primate psychologists have documented mutual gazing in both monkeys and apes, and have observed one monkey following the gaze of another. They also now recognize that nonhuman apes (chimpanzees, for example) will sometimes signal by pointing with a hand or finger—especially if they were reared in close association with human role models.59 Even if mirror neurons turn out to be important for understanding how individuals come to empathize with others, by themselves mirror neurons could scarcely be sufficient to explain the development of human-caliber empathy, since other primates possess mirror neurons as well.
Then in a stunning reversal of something behavioral scientists had long taken for granted, comparative psychologists discovered that chimpanzee newborns sometimes fixate on eyes, seek out faces, gaze into others’ eyes, and even engage in Meltzoffian-style imitation of facial expressions. The neural equipment that supposedly allowed humans to read intentions and minds is right there in baby chimpanzees and possibly other primates as well.
Mothers and Others Page 6
