We have now brought our story—our fragmentary effort to reconstruct some of the entries in the orphan’s file, to cast a little light into the shadows—to the threshold of the appearance of humans on Earth. It is time to take stock.

Many of the protective ditches, moats, and minefields painstakingly dug to separate us from the other animals have now been bridged or flanked. Those driven to preserve for us some unique, unambiguous, defining characteristic are tempted to shift the definitions once again and erect a final line of defense around our thoughts. If chimpanzee and bonobo language is limited, we cannot tell much about what they think or feel, what meaning, if any, they give to their lives. They have authored, at least so far, no autobiographies, reflective essays, confessions, self-analyses, or philosophical memoirs. If we can choose particular ideas and feelings to define ourselves, no chimp can contradict us. For example, we might point to our knowledge that all of us will someday die, or that sex is the cause of babies—matters widely understood among humans, although sometimes denied. Perhaps no ape has ever glimpsed these important truths. Perhaps some have. We do not know.² But standing alone on such homiletic pinnacles is a hollow victory for the human species. These occasional insights are minor matters compared to the vaunted distinctions of humanity that have crumbled into dust as we have learned more about the other animals. At so fine a level of detail, the motives of those who would define us by this or that idea seem suspect, the human chauvinism manifest.

To compare humans with other animals in regard to behavior amenable to observation is just; but unfavorable comparisons on the basis of first-person accounts emanating from within the animals themselves, their reports of their thoughts and insights, are unfair if no channel of communication into their internal lives has yet been opened. Absence of evidence is not evidence of absence. Were we better able to enter into the mind of the ape, might we not find much more there than we guess?—a point made almost three centuries ago by Henry St. John, the first Viscount Bolingbroke:

An oft-cited difference purported to exist between human beings and other animals is religion. Only humans, it is said, have religion, and that settles the matter. But what is religion? How could we know whether animals have it? In The Descent of Man, Darwin cites the comment, “a dog looks on his master as a god.” Ambrose Bierce⁴ defined reverence as “the spiritual attitude of a man to a god and a dog to a man.” The omega looks on the alpha as something like a god, and the depths of his submission and self-abasement are reached in few extant religions. It is hard to know how profoundly dogs or apes feel reverence, how tinged with awe their attitudes are toward a stern “master” or a well-established alpha, whether they have a sense of the sacred, pray for forgiveness, and otherwise seek to placate and influence forces more powerful than they. Animals raised, educated, and disciplined by much stronger and wiser parents, animals spring-loaded to fit into a dominance hierarchy, animals moreover faced with the daunting presence of human beings armed with life-and-death powers and meting out rewards and punishment—such animals may well have feelings akin to what we call religious. Many mammals and all primates satisfy these conditions.

Over the course of human history, some religions, it is true, have become much more than this—at their best transcending intimidation, hierarchy, and bureaucracy, while providing comfort for the powerless. A few, rare, religious teachers have acted as a conscience for our species, have inspired millions by the example of their lives, have helped us to break out of baboonish lockstep. But none of this contradicts the thesis that a generalized religious predisposition, ready to be put to use by the local social structure, may be a commonplace in the kingdom of the animals.

Perhaps, if we were able to peer into the mind of the ape in a state of nature, we would find—among a flurry of other feelings—a sense of satisfaction about its apeness rivaling ours about our humanity. Every species may feel something similar. It would be far more adaptive than its opposite. If anything like this is true, then we would be denied even our self-congratulatory distinction of being the only animal that makes self-congratulatory distinctions.

If we have not much peered into the hearts and minds of other species and have not even studied them carefully, we may impute to them virtues and strengths as well as vices and deficiencies that in fact they lack. Consider this bit of verse by the poet Walt Whitman:

On the basis of the evidence presented in this book, we doubt if any of Whitman’s six purported differences between other animals and humans is true—at least given a little poetic license; that is, in the spirit if not the letter of the poem. Montaigne thought⁶ that when we conclude that other animals have “ambition, jealousy, envy, revenge, superstition, and despair,” we are simply projecting our own “sickly qualities” onto the beasts; but this goes too far, as the lives of the chimps make clear. While many commentators have exaggerated the differences between humans and “animals” and warned of anthropomorphizing, others, like Whitman and Montaigne, have romanticized and sentimentalized the animals. Both excesses serve to deny our kinship.

——

The proximate cause of human success must have something to do with the conjoining of our intelligence and our talent for making and using tools. Surely, our globe-girdling civilization arises chiefly from these two abilities. Without them, we would be nearly defenseless. But “a little dose … of judgment or reason often comes into play, even in animals very low in the scale of nature,” Darwin wrote in The Origin. Late in life, he made extensive studies of what you might think is an unpromising subject, the intelligence of earthworms. He gave them intelligence tests involving the manipulation of real and artificial leaves. They did very well. Flatworms can work their way through a simple maze to get a reward; even worms have a degree of intelligence. Galapagos woodpecker finches, studied by Darwin on the voyage of the Beagle, use twigs to worry wood-dwelling larvae out of branches; even birds have a rudimentary technology.

Certainly we could not have invented civilization without intelligence and technology. But it would be unfair to describe civilization as the determining characteristic of our species, or as establishing the level of intelligence and manual dexterity required for our definition, especially because the first 99 percent of the tenure of humans on Earth was spent in an uncivilized state. We were humans then, as now, but we hadn’t dreamed up civilization. Yet the fossil remains of the earliest known humans and hominids—dating back not just hundreds of thousands but millions of years—are often accompanied by stone tools. We had the talents, at least in partial measure. We just hadn’t gotten around to civilization yet.

The contrast between the proclivity for tools in humans and the absence of tool use in so many other animals has made it tempting to define ourselves as the tool-using or the tool-making animal—as seems to have first been suggested by one of the members of Josiah Wedgwood’s and Erasmus Darwin’s Lunar Society, Benjamin Franklin. On April 7, 1778, James Boswell confesses to admiring Franklin’s definition. The ever-grumpy and sometimes over-literal Samuel Johnson objects: “But many a man never made a tool; and suppose a man without arms, he could not make a tool.” Again, if we are to define a human being, should we use traits that, without exception, every human being possesses, or traits that may be present only potentially? And if the latter, who knows what traits lie smoldering in other animals, not yet fully elicited by circumstance or necessity?

——

Blasé, matter-of-fact, encumbered by the infant (who, face to her chest, clutches her fur), she carefully positions the hard-shelled fruit on the log and smashes it open—using a stone tool procured for the purpose. Hammer and anvil. No light bulb goes off above her head. There’s no chin to fist, no hint of insight struggling to emerge, no moment of revelation, no strains from Also Sprach Zarathustra. It’s just another routine, humdrum thing that chimps do. Only humans, who know where tools can lead, find it remarkable.

Although many chimps literally do not know enough to come in out of the rain, they’re able to use tools. Not only that: they’re able to premeditate the use of tools—to acquire a tool now for some action they intend to perform later. They go large distances to find the right kind of stone or stick, and then lug it home. They seem to have had its ultimate use in mind all the while.

“It has often been said,” wrote Darwin in The Descent of Man, “that no animal uses any tool; but the chimpanzee in a state of nature cracks a native fruit, somewhat like a walnut, with a stone.” His source was that acute but easily offended Victorian observer of chimps, Thomas Savage, M.D. Chimpanzees regularly crack open hard-shell seeds and nuts with a stone hammer against a stone or wooden anvil; and they’ll carry the appropriate rocks over a good fraction of a kilometer for the purpose. At other times, wooden clubs may be used as nutcrackers. In the Tai Forest in the Ivory Coast, chimps select an appropriate club, climb a cola tree, pick the choice cola nuts, and crack them open using the branch as the anvil and the club as the hammer.⁷ Female chimps are more likely to employ hammer-and-anvil technology than males, and they’re better at it.*

A chimp breaks off a long grass stalk or a reed so she may use it later, hundreds of meters away, more than an hour in the future, to lure delectable termites out of a log or termite mound. She must remove superfluous leaves and twigs, shape it, shorten it, insert it into the termite tunnel with a deft twisting motion to follow the interior contours, shake it seductively to attract termites onto it, and then with great care remove it without scraping off too many. Chimps take years to perfect their technique and routinely teach it to their young, who are avid pupils. This exactly satisfies one confident definition of “the uniqueness of man’s toolmaking”—namely, “the fashioning, out of natural materials, of an implement designed to be used at a distant time and on objects not now perceptually present.”¹⁰

How difficult is chimpanzee termite fishing? What depth of intellect and manual dexterity are required? Suppose you are dropped naked into the Gombe Preserve in Tanzania and, like it or not, discover that termites are your principal hedge against malnutrition or starvation. You know they’re an excellent source of protein; you know that self-respecting humans in many parts of the world regularly eat them. You manage to put aside whatever compunctions you may feel. But catching them one at a time is not going to be worth the effort. Unless you’re lucky enough to encounter them when they’re swarming, you’re going to have to make a tool, repeatedly insert it into their meter-high mound, introduce the tool into your mouth, and strip off the clinging termites with your teeth and lips as you withdraw the tool from your mouth. Could you do as well as a chimp?

The anthropologist Geza Teleki tried to find out. He spent months in Gombe under the tutelage of a chimp named Leakey, who was adept at the technique. Teleki wrote about his findings in a famous scientific paper called “Chimpanzee Subsistence Technology.”¹¹ The Gombe termites mainly come out at night; before dawn they expertly wall up all the entrances to their mounds. Chimps routinely begin their termite foraging by scraping away these entrance barriers. Teleki’s inquiry started there:

Next, Teleki looked into a selection of raw materials for the manufacture of the termite probe:

Finally, putting aside the difficulties in finding the tunnel entrances and manufacturing the tools, Teleki set himself to learning how to use a competently produced tool:

It is a little daunting to discover—on the very technological grounds on which human superiority is often claimed—that after months of apprenticeship, human scientists cannot do as well as preadolescent chimps. Teleki remained generous and good-natured about his failure. In the acknowledgments at the end of the paper, among thanks to various organizations for financial and logistical support, there appears this sentence: “I am, in addition, more than grateful to the patient and tolerant Leakey, whose termite-collecting skills so outstripped mine.”

The chimp style of teaching nut cracking and termite fishing to the young is relaxed—by example and not by rote. The student fiddles with the tools and tries out various approaches, rather than slavishly copying every hand movement of the instructor. Gradually the technique improves. Chimps have for this reason been criticized¹² as not really having culture. (Ironically, one group of scientists denies chimps language because—as we described earlier—they are said to be too imitative, while another group of scientists denies chimps culture because they are said to be not imitative enough.)

The learning style of the great physicist Enrico Fermi was to ask colleagues to state the problems they had recently solved, but to withhold their answers: He could understand the problem only by working it through himself. Learning by doing is—in science and technology, as in many other human activities—much more effective than learning by rote. Knowing, as the chimps do, that a problem exists and can be solved with the tools at hand is most of the battle.

Baboons in Gombe eat termites, but almost entirely during the two- or three-week period in which the insects migrate. Then the baboons can be seen gathering and slurping the insects, and leaping into the air to catch them on the wing. In less bountiful times, baboons will be shooed away from a termite mound by an arriving group of chimpanzees. Sometimes the displaced baboons sit a little distance away, morosely observing the chimps working away with their tools on the mound. When the chimps are done, they leave their modified stalks and reeds at the base of the mound. But no baboon has ever been observed trying to use an abandoned tool—even though it could extend their termite season from weeks to months. Apparently the baboons just don’t have it in them. They’re not smart enough. Probably their brains are too small.

As chimps are much better than baboons at collecting termites, so some preindustrial humans who routinely eat termites are much better than chimps. They dig open the termite mounds, or fumigate them, or flood them with water. One of the more elegant practices is—with the tongue on the palate, or two pieces of wood gently touched to the mound’s surface—to imitate the sound of raindrops, which entices the termites out of their nest.¹³ Chimps have never been observed to use these techniques.* Probably they’re not smart enough. Probably their brains are too small.

What we find most interesting is the overlap. Some chimps lack even probe technology, and are no better at catching termites than baboons are. Other chimps are armed with a well-developed if rudimentary technology, many steps having to be done correctly and in the right sequence for the method to work—as good as many human cultures, although nowhere near as good as some. There are human cultures barely up to the highest chimpanzee standards of termite catching, and others only on a par with the baboons.¹⁵ No sharp boundaries are apparent here separating baboons from chimps, or chimps from humans.

Chimps also drop branches on intruders and sop up drinking water with leaves. While they cannot be described as fastidious or obsessively hygienic, chimps are known to use leaves as toilet paper and handkerchiefs, and twigs as toothbrushes. They employ sticks for digging up roots, for investigating animals in burrows and knotholes, and—like a croupier at a gaming table—for raking in otherwise inaccessible fruit. If they were able to manufacture more complex tools, they certainly would have the intelligence and dexterity to use them: In zoos, chimps try to steal the keys from the keeper’s pocket. When successful, they often manage to open the lock. Like us, they can sometimes use their intelligence to escape from bondage.

Male chimps like to throw missiles—whatever is handy, generally sticks and stones. (Like the inmates of college fraternity houses, they also occasionally throw food.) Females are much less interested in missiles. Chimps would throw stones at the visitors who gawk at them in the traditional kind of zoo—if they had stones. As it is, all they have is feces. When wild chimps are presented with a fairly realistic mechanical leopard, after a reassurance frenzy of screams, hugs, and mutual mountings, they find appropriate clubs and beat the effigy to death—or at least until they knock the stuffing out. Or they’ll pelt it with stones. (In the same circumstance, baboons will furiously attack the leopard, but without a thought of using clubs. Baboons just don’t know about tools.)

Chimps have stunned or killed by throwing stones. The directionality of their throwing is good. Where they’re deficient is in range: In tense confrontations with prey or hostile peers, thrown rocks hit their targets only a few percent of the time. Adolescent boys don’t do much better under comparable conditions. But even when inaccurate, a hail of stones can be off-putting.

A distinction needs to be made between tool using and tool making. Many scientists have conceded tool use to other animals, and, following Benjamin Franklin, defined humans as the sole tool-making animal; where tools are manufactured, it is suggested, language cannot be far behind.¹⁶ But the chimpanzee termite fishery industry makes it clear that chimps, with considerable forethought, both make and use tools. Chimps also have a rudimentary stone technology, although, as far as we know, they don’t manufacture stone tools in the wild. In captivity, though, Kanzi—the linguistically talented bonobo—has, imitating human models, hit stones together to produce sharp flakes, which he then uses to cut a string so he can open a box which is filled with food. (This is a causality sequence at least five steps long.) As long as it’s sharp enough to cut the string, Kanzi will generally settle for the first crude stone knife he flakes off. But the thicker the rope he must cut, the larger and sharper the knife he makes.¹⁷

Evidence of chimpanzee talent to combine objects purposefully to make tools has actually been with us for decades:

It’s not hard to imagine an especially insightful chimp or bonobo wondering if there weren’t some way to make a stone flake cut better or a projectile go farther.

Since the progress of human technology is a continuum, to pick a particular milestone—the domestication of fire, say, or the invention of the bow and arrow, agriculture, canals, metallurgy, cities, books, steam, electricity, nuclear weapons, or spaceflight—as the criterion of our humanity would be not just arbitrary, but would exclude from humanity every one of our ancestors who lived before the selected invention or discovery was made. There is no particular technology that makes us human; at best it could only be technology in general, or a propensity for technology. But that we share with others.

Like us, nonhuman primates are not all the same. They vary in focus from individual to individual and group to group. Some, like Imo, are technological geniuses. Others, like the hierarchy-besotted macaque males, are hopelessly old-fashioned and stuck in their ways. One chimp population pounds nuts, another does not. Some probe for termites, others only for ants. Some use grass stalks and vines to coax the insects out, others sticks and twigs. Females preferentially use hammers and anvils, males preferentially throw stones. None of them, so far as we know, has ever used a stick to dig out a nutritious root or tuber, although it ought to be possible and adaptive. Some individuals find technology uncongenial or intellectually too taxing and never use it, despite the obvious advantages accruing to other members of their group who are comfortable with technology. Some large groups have no technology at all. “I’m embarrassed to say,” says an observer of a community of Ugandan chimps, “that the Kibale chimpanzees appear as the country bumpkins of the chimp world.” He goes on to speculate that life is too easy and food too plentiful at Kibale for the challenge of deprivation to elicit the response of technology.¹⁹

Chimps are smart. They carry accurate mental maps of their territory in their heads. They seem to know the seasonal availability of plant foods and will congregate in some peripheral province of their territory to harvest a small stand of ripening fruits or vegetables. They have rudimentary culture, medicine, and technology. They have a startling capacity for simple language. They can plan for the future. Think again of the sensory and cognitive skills necessary to succeed in chimpanzee social life. You must recognize dozens of faces and their expressions. You must remember what each of these individuals has done to you or for you in the past. You must understand the foibles, weaknesses, ambitions of potential allies and rivals. You must be quick on your feet. You must be very flexible. But if you have all this, there’s probably a great deal else about the world that, sooner or later, you can figure out and change.

——

How thoroughly the chimps and bonobos have erased the list of purported human distinctions!—self-awareness, language, ideas and their association, reason, trade, play, choice, courage, love and altruism, laughter, concealed ovulation, kissing, face-to-face sex, female orgasm, division of labor, cannibalism, art, music, politics, and featherless bipedalism, besides tool using, tool making, and much else. Philosophers and scientists confidently offer up traits said to be uniquely human, and the apes casually knock them down—toppling the pretension that humans constitute some sort of biological aristocracy among the beings of Earth. Instead, we are more like the nouveau riche, incompletely accommodated to our recent exalted state, insecure about who we are, and trying to put as much distance as possible between us and our humble origins. It’s as if our nearest relatives, by their very existence, refute all our explanations and justifications. So as counterweights to human arrogance and pride, it is good for us that there are still apes on Earth.

Much of this chimp and bonobo behavior was discovered only recently. Doubtless they have other talents that have so far eluded us. We humans are biased observers, with a vested interest in the answer. The cure for this disease is more data. But the study of primate behavior, both in the laboratory and in the wild, is by and large poorly and grudgingly funded.

If we insist on absolute rather than relative differences, we do not, so far at least, discover any distinguishing characteristic of our species. Shouldn’t we expect, especially with our close relatives, that the differences will be of degree and not of kind? Isn’t this the lesson of evolution? If we require that we uniquely possess tools, culture, language, trade, art, dance, music, religion, or conceptual intelligence, we will not understand who we are. If, on the other hand, we are willing to admit that what distinguishes us from the other animals is more of one propensity and less of another, then we may make some progress. Then, if we wish, we can take pride in the fuller flowering of primate aptitudes that has taken place in our species.

The more an animal weighs, the more of it there is that its brain must control, and so—within certain limits—the bigger its brain needs to be. This is true between species, although not between individual members of a given species. A species with a much bigger brain for its body weight—especially in its higher brain centers—has a good chance of being, on some level, smarter. Indeed, for comparable body weights, humans tend to have bigger brains than other primates; primates than other mammals; mammals than birds; birds than fish; and fish than reptiles.²⁰ There is some scatter in the data, but the correlation is clear. It corresponds pretty well to the commonly accepted (by humans, of course) rank order of animal intelligence. The earliest mammals had significantly larger brains than their reptilian contemporaries of comparable body weight; and the earliest primates were similiarly well-endowed compared to other mammals. We come from big-brained stock.

Adult humans, who weigh only a little more than adult chimps, nevertheless have brains three to four times more massive. A human infant a few months old already has a larger brain than a grown-up chimpanzee.²¹ It seems very likely that we’re significantly smarter than the chimps because we have a significantly larger brain—despite the comparable body weights. For a factor of three to four increase in brain weight, the brain size (its circumference, say) must increase by about 50%. But the human brain isn’t entirely a proportional scaling up of a chimp brain. Despite what Huxley found, there is a little bit of brain architecture—not much, but some—that humans have and the other primates at least mainly don’t. Significantly, some of it seems to be related to speech.

Some parts of the brain are proportionally much larger in humans than in other primates: The cerebral cortex in general, responsible for thinking, is proportionally much larger in humans than in chimps (or in our non-human primate ancestors); so is the cerebellum, in charge of keeping us steady on our (two) feet.²² The frontal lobes are far more prominent in humans than in chimps; they’re thought to play an important role in foreseeing the future consequences of present action, in planning ahead.*

Still, purported distinctions in brain anatomy must be treated with caution: There are many primates not yet studied with sufficient care, and there have been so many erroneous claims. For example, in humans different information is stored in, and different abilities controlled by, the two hemispheres of the cerebral cortex—a surprising finding that emerges from patients whose bundle of neural fibers connecting the two brain hemispheres has been cut.²³ This asymmetry, called “lateralization,” is connected with language, and, arguably, with tool use.²⁴ So, of course, the conceit arose that only the brains of humans are lateralized.²⁵ Then songbirds were found to have their songs stored almost exclusively in only one hemisphere of their brains,²⁶ and lateralization was discovered in chimps that had learned language.²⁷ In any case, the qualitative differences between chimp and human brains, if any, are few and subtle.

So is that all there is to it? Give the chimps a bigger brain and the power of articulate speech, maybe take away some testosterone, cancel the ads for ovulation, burden them with some more inhibitions, give them a shave and a haircut, stand them up on their hind legs, and get them out of the trees at night? Would they then be indistinguishable from the earliest humans?

The possibility that we might be “no more than” deluxe model apes, that the differences between them and us might be almost wholly differences of degree and not of kind, and that the differences of kind, if they exist, might be elusive—all this was a source of profound discomfort from the earliest days in which human evolution was seriously considered. Just a few years after The Origin of Species was published, Huxley wrote:

Suppose you own a personal computer. It’s roughly the size of a typewriter, sits on your desk, and outcomputes any hundred mathematicians. There was nothing remotely like it on Earth only a few decades ago. Building on the strengths of this model, the manufacturer now introduces a relatively minor variant with a faster and more powerful microprocessor and a few new peripherals. Surely this is not as remarkable an accomplishment as the invention of the personal computer in the first place. But the new computer, you find, can perform a range of functions the old one couldn’t. It can figure certain problems out in a reasonable span of time that previously would have taken—for all intents and purposes—forever. There are whole categories of problems you can now solve that you couldn’t come within hailing distance of before. But if solving these problems were somehow important for the survival of the personal computer, pretty soon there would be a large number of personal computers with the added capabilities. Perhaps our uniqueness is no more than, or only a little more than, this: an enhancement of well-established pre-existing talents for invention, forethought, language, and general intelligence, enough to cross a threshold in our capacity to understand and change the world.

Still, depending on what else they are allied with, greater reasoning skills need not—necessarily and in all circumstances—be adaptive and improve survival. “Reason more than anything else is man,”²⁹ said Aristotle. Mark Twain countered:

If we imagine that we are purely, or even mainly, rational beings, we will never know ourselves.

We are too weak to destroy or seriously damage the planet, or to extinguish all life on Earth. That is far beyond our powers. But what we can do is to destroy our global civilization and, just possibly, sufficiently alter the environment as to render our own species, along with vast numbers of others, extinct.³¹ Even at levels far short of those that can cause our extinction, our technology has given us awesome powers—our ancestors would have thought them god-like. This is merely a statement of fact. It is not a remonstrance and is not intended to define us. But it leads us back again to the question of whether we have any choice in the matter, or whether there is some deeply buried part of our nature that, despite the comparative intelligence and promise of our species, will sooner or later arrange matters for the worst.

“We are conscious of an animal in us,” wrote Henry David Thoreau, “which awakens in proportion as our higher nature slumbers.”³² The idea is, in a way, obvious; it emerges from even shallow introspection. It goes back at least to Plato,³³ who described how in dreams, “when the gentler part of the soul slumbers and the control of Reason is withdrawn … the Wild Beast in us … becomes rampant.” That Wild Beast, Plato goes on, “will cast off all shame and prudence at such moments and stop at nothing”—including incest, murder, and “forbidden food.” The idea of the beast within is also familiar to us from Sigmund Freud, who called it the “id,” Latin for “it,” and from neurophysiology, starting with the work of J. Hughlings Jackson.³⁴ A more recent incarnation can be found in the perspective of the neurophysiologist Paul MacLean,³⁵ who identifies many of the control centers for sex, aggression, dominance, and territoriality in a deep-lying, ancient part of the brain called the R-complex—“R” for reptile, because we share it with the reptiles, who lack much of a cerebral cortex, the seat of consciousness.

We go to great lengths to deny our animal heritage, and not just in scientific and philosophical discourse. You can glimpse the denial in the shaving of men’s faces; in clothing and other adornments; in the great lengths gone to in the preparation of meat to disguise the fact that an animal is being killed, flayed, and eaten. The common primate practice of pseudosexual mounting of males by males to express dominance is not widespread in humans, and some have taken comfort from this fact. But the most potent form of verbal abuse in English and many other languages is “Fuck you,” with the pronoun “I” implicit at the beginning. The speaker is vividly asserting his claim to higher status, and his contempt for those he considers subordinate. Characteristically, humans have converted a postural image into a linguistic one with barely a change in nuance. The phrase is uttered millions of times each day, all over the planet, with hardly anyone stopping to think what it means. Often, it escapes our lips unbidden. It is satisfying to say. It serves its purpose. It is a badge of the primate order, revealing something of our nature despite all our denials and pretensions.

The danger seems so obvious. Surely there is something in us deeply seated, self-propelled, and on occasion able to evade our conscious control—something that can do harm despite what we understand to be our best intentions: “The good that I would I do not; but the evil which I would not, that I do.”³⁶

Sometimes, we use our “higher nature,” our Reason, to awaken the Wild Beast. It’s that stirring animal that terrifies us. If we acknowledge its presence, some fear, we will be sliding toward a perilous fatalism: “That’s what I’m like,” the criminal might plead. “I’ve tried to behave myself, abide by the law, be a good citizen, but there’s only so much you can ask of me. I’ve got an animal inside. It’s human nature, after all. I’m not responsible for my actions. Testosterone made me do it.”³⁷ Such views, if widely held, could unravel the social fabric, it is feared; therefore, it is better to suppress knowledge of our “animal” natures and pretend that those who perceive and discuss such natures are undermining human self-confidence and playing with fire.

Maybe what we’re afraid we’ll find if we look too closely is some resolute malevolence lurking in the heart of man, some unquenchable selfishness and blood lust; that down deep we’re all mindless crocodilian killing machines. It’s an uncomplimentary self-image and of course, if widely held, it would work to undermine human self-confidence. In an age when the global environment is within our power to ruin, the notion is not cheering for our future prospects.

What is odd about this point of view—apart from the notion that criminals and sociopaths really take heart from the scientific finding that humans have evolved from other animals—is how selectively it makes contact with the data about animals and, especially, about our closest relatives, the primates. There we can also find friendship, altruism, love, fidelity, courage, intelligence, invention, curiosity, forethought, and a host of other characteristics that we humans should be glad to have in greater measure. Those who deny or decry our “animal” natures underestimate what those natures are. Isn’t there much to be proud of, as well as to be ashamed of, in the lives of the monkeys and apes? Shouldn’t we be glad to acknowledge a connection with Imo, Lucy, Sultan, Leakey, and Kanzi? Remember those macaques who would rather go hungry than profit from harming their fellows; might we have a more optimistic view of the human future if we were sure our ethics were up to their standards?

And if our intelligence is our distinction, and if there are at least two sides to human nature, shouldn’t we be sure to use that intelligence to encourage the one side and restrain the other? When we reconfigure our social structures—and in the last few centuries we’ve been tinkering with them like mad—isn’t it better and safer to have our best understanding of human nature firmly in mind?

Plato was afraid that when the superimposed social controls are slumbering, the wild beast within will incline us to incest “with a mother or anyone else, man, god, or brute,” and other crimes. But monkeys and apes and other “wild beasts” hardly ever commit parent-child or sibling-sibling incest. The inhibitions are already up and running in other primates, and for good evolutionary reasons. We demean the other animals when we attribute to them whatever predispositions to incest we find in ourselves. Plato feared that the animal within will incline us to “any deed of blood.” But monkeys and apes and other “wild beasts” are powerfully inhibited against shedding blood, at least within the group. The established lexicon of dominance and submission, friendships, alliances, and sexual partnerships keeps real crimes of violence down to a dull roar. Mass murder is unknown. True main-force warfare has never been observed. Again, we undervalue our non-human ancestors when we blame them for our violent proclivities. Very likely, they had inhibitions in place that we routinely circumvent.

Killing an enemy with teeth and bare hands is emotionally far more demanding than pulling a trigger or pressing a button. In inventing tools and weapons, in contriving civilization, we have disinhibited the controls—sometimes thoughtlessly and inadvertently, but sometimes with cool premeditation. If the beasts who are our nearest relatives engaged recklessly in incest and mass murder, they would have rendered themselves extinct. If our non-human ancestors did, we would not be here. For the deficiencies of the human condition, we have only ourselves and our statecraft to blame—not the “wild beasts,” and not our distant ancestors, who cannot defend themselves against self-serving accusations.

There is no reason for despair or timidity here. What we should be ashamed of is the counsel that urges us to avoid self-doubt even at the cost of hiding our nature from ourselves. We can solve our problems only if we know who it is we’re dealing with. To balance whatever dangerous tendencies we perceive in ourselves is the knowledge that in our ancestors and close relatives, violence is inhibited, controlled, and, in encounters within the species at least, devoted mainly to symbolic ends; that we are gifted in making alliances and friendships, that politics is our business, that we are capable of self-knowledge and new forms of social organization; and that we are able, better than any species that ever lived on Earth, to figure things out and to build things that never were.

Even in the fossil remains of the earliest lifeforms, there is unmistakable evidence of communal living arrangements and mutual cooperation. We humans have been able to design effective cultures that for hundreds of thousands of years have fostered one set of inborn characteristics and discouraged another. From brain anatomy, human behavior, personal introspection, the annals of recorded history, the fossil record, DNA sequencing, and the behavior of our closest relatives, a clear lesson emerges: There is more than one side to human nature. If our greater intelligence is the hallmark of our species, then we should use it as all the other beings use their distinctive advantages—to help ensure that their offspring prosper and their heredity is passed on. It is our business to understand that some predilections we bear as remnants of our evolutionary history, when coupled with our intelligence—especially with intelligence in the subordinate role—might threaten our future. Our intelligence is imperfect, surely, and newly arisen; the ease with which it can be sweet-talked, overwhelmed, or subverted by other hardwired propensities—sometimes themselves disguised as the cool light of reason—is worrisome. But if intelligence is our only edge, we must learn to use it better, to sharpen it, to understand its limitations and deficiencies—to use it as cats use stealth, as walking sticks use camouflage, to make it the tool of our survival.