NONFICTION SECTIONS of our bookstores feature two radically different kinds of books on the human condition. They update the age-old question — do humans soar with the angels or grovel with the beasts — by arguing for or against human exceptionalism.

The first kind of book still assumes humans are the crown of creation, but now resorts to highlighting our “glorious” free will, consciousness, morality, culture, and so on. Many anthropology books dance around this theme, not denying evolution per se but presenting humans as “a spectacular evolutionary anomaly.” Other animals are invoked not so much for what they can do, but for what they cannot do.

The second kind of book resolutely insists on a biological framework, describing us as one animal among many and stressing our kinship with other species. In this regard, consider the amygdala, that pea-shaped part of the brain that has recently received so much press. Activated by both fear in rats and phobias in humans, it has a common function across species. Last year’s Behave by Robert Sapolsky, a Stanford primatologist and neuroscientist, exemplifies this second type of book, insisting on the neural organization and transmitters we share with all other mammals.

As a student of animal behavior, I won’t hide my overwhelming preference for the second approach, especially after the last few decades when cognitive science has blown big drafty holes in the wall supposedly separating us from the rest of nature. Focusing on human uniqueness is like having eyes only for the tip of the iceberg, whereas we need to grasp the whole submerged mountain to know where we come from. Books that set us apart face the problem not just of shrinking evidence, but also of evolutionary continuity: how to reconcile the slow and smooth transitions of evolution with the assumption that humans represent a fundamental departure? William James, the founder of American psychology, pointed out this dilemma more than a century ago. He predicted that if we keep assuming that humans alone are thinking, self-aware beings, then we’ll have great trouble explaining our origin: “We ought ourselves sincerely to try every possible mode of conceiving the dawn of consciousness so that it may not appear equivalent to the irruption into the universe of a new nature, non-existent until then.

Cecilia Heyes’s Cognitive Gadgets addresses the perceived human difference by proposing precisely the kind of irruption James warned against. A British expert of animal cognition, Heyes has made waves in her country by questioning nearly every new discovery in this burgeoning field. When chimpanzees were said to recognize their own reflection by inspecting a mark painted on their face, Heyes proposed that they just randomly touch themselves in front of a mirror. When it was reported that Japanese macaques learn how to wash sweet potatoes from watching each other, Heyes suggested that they very well might have been chased into the ocean while holding a spud. Simple associative learning, she argues, is the key to nearly everything animals do. While few of her armchair hypotheses have held up, it is no surprise that after decades of pooh-poohing the abilities of other species, Heyes needs a miracle to explain how we got where we are today. Her answer is that we have culturally invented new ways of learning. These are our “gadgets.” We are masters of imitation, for example, not because we possess mirror neurons or are endowed with a special instinct, but thanks to a uniquely human advance: matching the movements that we see with the movements that we make, and vice versa. Thus, a recent paper by Heyes carried the title: “Imitation: Not in Our Genes.” It’s a cultural innovation.

Her proposal for shoring up our exceptionality ignores the overwhelming evidence for spontaneous matching of movements in other species. Why else do we have the verb “aping”? Fireflies flash in unison, dolphins jump out of the water as one, and a monkey who watches another monkey press a button will press its own button in perfect synchrony. Heyes also downplays the fact that human copying starts so early in life that a cultural explanation is unlikely. It is well-documented, for example, that human babies stick out their tongue in response to an experimenter doing the same, a reaction also seen in other infant primates. Her denial that this even happens has her clashing with developmental psychologists, who went so far as to reanalyze the data in her favorite study. Instead of finding the “mortal blow” to neonatal imitation she had touted, they actually found support for it. Regardless of who is right here, the deeper problem is that Heyes tries to account for human exceptionalism by bypassing evolution, which doesn’t permit the sort of jumps she envisions. A cultural explanation is a poor alternative, though, because culture is by definition variable. It tells us why people differ from place to place, but does not account for traits that characterize our species as a whole. For this, we still need biology.

Explanations of human behavior grounded in biology are wonderfully straightforward. Instead of engaging in theoretical acrobatics à la Heyes, they stress commonalities across species — even with respect to the emotions. In The Emotional Foundations of Personality, the late Estonian-American neuroscientist Jaak Panksepp and his former student Kenneth L. Davis develop an evolutionary approach for understanding human personality. Panksepp founded the field of affective neuroscience, placing human and animal emotions on a continuum, and thus helping to make animal emotions a respectable topic. Known for his studies of joy and “laughter” in rats (registered in their ultrasonic vocalizations), he found that rats actively seek out tickling fingers, probably rewarded by opioids in their brains. His work went far beyond this arcane topic, however, situating emotions in ancient subcortical brain areas shared across all vertebrates rather than in our recently expanded cerebral cortex.

In their book, Panksepp and Davis challenge the so-called Big Five personality traits, still the most popular method for plotting human personality. Its method reflects blinding faith in the thousands of labels that we use to describe personality. A large number of them are thrown into a giant statistical “grinder” (as one critic called it) to see how they hang together. The end product is a factor analysis that usually yields five dimensions: openness, conscientiousness, extraversion, agreeableness, and neuroticism. In the old days, the computations were so burdensome that any graduate student who could complete them in four years was said to deserve a PhD. Today, we do them by computer obviously, but we still end up with the same five factors.

The method may be sophisticated, but unfortunately the theory behind it is largely nonexistent. Panksepp and Davis suggest that there is, in fact, little connection between the Big Five and their manifestations in daily life. For one thing, if we analyze adjectives in languages other than English, we often end up with a different number of dimensions. For another, the approach isn’t based on any ideas about how personalities come about in evolutionary terms, how they are expressed, or how they intersect with human biology and neuroscience. In one well-respected study, twins reared in the same household were found to be as similar in personality as twins reared apart. This means that genes are important drivers of personality, which may indeed also explain the parallels between human and animal personalities.

The book devotes several chapters to the temperaments of primates, dogs, rats, even fish. Anyone who has had two cats or two dogs at home knows how much their behavior varies. For my part, I have had aloof cats, who keep their distance, as well as cuddly ones who love to snuggle with both humans and their feline fellows. Panksepp and Davis recognize the same set of basic emotions in all mammals, and argue convincingly that we should ground the science of human personality in bio-drivers rather than linguistic labels. If we can apply genetic selection to the aggressiveness of fish, for example, then this hints at a biological personality trait grounded in an emotion, one called Rage/Anger by the authors, also found in other species, including our own.

The third book under discussion, Alan Jasanoff’s The Biological Mind, is the most accessible, written in an engaging style and with a clear message. He mobilizes his culinary experience in passages like this one: “When I first touched a brain, it was braised and enveloped in a blanket of beaten eggs.” This is certainly one way to evoke the brain-body connection! Since the brain is part of the body in humans as in other species, argues Jasanoff, we should never consider one without the other. Director of the MIT Center for Neurobiological Engineering, he strenuously objects to any hint of dualism between body and mind according to which the brain is in charge. In other words, we can’t say “we are our brain” without also saying we are our body. The brain is connected in a million and more ways to the body, and shaped by everything that happens to it and in it.

A patient’s personality may change after an organ transplant, for example, seemingly adopting part of the donor’s proclivities. Thus, the recipient of a cyclist’s heart may suddenly become a cycling enthusiast. There is also evidence that altering someone’s gut microbiome via a fecal transplant can affect their mental health. These are certainly interesting examples of how the body affects the mind, but the best-documented effects involve the bodily states known as emotions. We describe our emotions in visceral terms for good reason: every one of them arises in the body. Here, too, William James had something insightful to say, claiming that bodily changes accompanying an emotion are not just an expression of it: they are the emotion. Our guts are wrenched by sadness, our blood boils in anger, our heart throbs with infatuation, and so on. Moreover, we are by no means exceptional in this regard. We make ourselves large in anger or get “cold feet” when afraid, similar to the temperature drop in the feet and tail of a scared rat.

Jasanoff rightly objects to the cerebral mystique known as “neuroessentialism,” which reduces our lives and societies to the workings of the human brain. The idea that the brain can be hacked or digitally preserved is one rather extreme manifestation of this view — and in places like Silicon Valley, cryogenically freezing one’s head is now a fad. Wannabe immortalists anticipate the day when their brain’s contents will be “uploaded” to a machine. They are willing to pay a fortune for such a digitally immortal future. Never mind that science hardly knows what a mind without a body would look or feel like — or indeed whether waking up in digital format would constitute a happy moment. Happiness is a bodily state in humans as in other animals, and a brain severed from the body probably doesn’t feel much.

To drive this point home, Jasanoff’s final chapter imagines his own brain in a vat. He, or “it,” can still explore the world to satisfy his curiosity, but because these adventures lack corporal movement or embodiment, they are rather boring and lacking in purpose. The notion that the brain can live by itself undoubtedly stems from the absurd metaphor that brains are machines. Many of us fall for this metaphor even though the brain looks much more like soup than a computer. As Jasanoff writes:

The true brain is a grimy affair, swamped with fluids, chemicals, and glue-like cells called glia. The centerpiece of our biological mind is more like our other organs than a man-made device, but the ways we think and talk about it often misrepresents its true nature.

For me as a biologist, we live in happy times with so many books that expertly treat where we come from, who we are, and how we operate. So long as these books resist the temptation, so prevalent in our culture, to treat the human mind as its own creation, they will, I hope, over time encourage us to embrace our kinship with both the beast within and the beasts without, and consider the angels and our closeness to them just a figment of our imagination.


Frans de Waal, a primatologist and professor of psychology at Emory University, is the author of Are We Smart Enough to Know How Smart Animals Are? (Norton, 2016).