For 2,000 years, there was an intuitive, elegant, compelling picture of how the world worked. It was called “the ladder of nature.” In the canonical version, God was at the top, followed by angels, who were followed by humans. Then came the animals, starting with noble wild beasts and descending to domestic animals and insects. Human animals followed the scheme, too. Women ranked lower than men, and children were beneath them. The ladder of nature was a scientific picture, but it was also a moral and political one. It was only natural that creatures higher up would have dominion over those lower down.


Darwin’s theory of evolution by natural selection delivered a serious blow to this conception. Natural selection is a blind historical process, stripped of moral hierarchy. A cockroach is just as well adapted to its environment as I am to mine. In fact, the bug may be better adapted—cockroaches have been around a lot longer than humans have, and may well survive after we are gone. But the very word evolution can imply a progression—New Agers talk about becoming “more evolved”—and in the 19th century, it was still common to translate evolutionary ideas into ladder-of-nature terms.

Modern biological science has in principle rejected the ladder of nature. But the intuitive picture is still powerful. In particular, the idea that children and nonhuman animals are lesser beings has been surprisingly persistent. Even scientists often act as if children and animals are defective adult humans, defined by the abilities we have and they don’t. Neuroscientists, for example, sometimes compare brain-damaged adults to children and animals.

We always should have been suspicious of this picture, but now we have no excuse for continuing with it. In the past 30 years, research has explored the distinctive ways in which children as well as animals think, and the discoveries deal the coup de grâce to the ladder of nature. The primatologist Frans de Waal has been at the forefront of the animal research, and its most important public voice. In Are We Smart Enough to Know How Smart Animals Are?, he makes a passionate and convincing case for the sophistication of nonhuman minds.

De Waal outlines both the exciting new results and the troubled history of the field. The study of animal minds was long divided between what are sometimes called “scoffers” and “boosters.” Scoffers refused to acknowledge that animals could think at all: Behaviorism—the idea that scientists shouldn’t talk about minds, only about stimuli and responses—stuck around in animal research long after it had been discredited in the rest of psychology. Boosters often relied on anecdotes and anthropomorphism instead of experiments. De Waal notes that there isn’t even a good general name for the new field of research. Animal cognition ignores the fact that humans are animals too. De Waal argues for evolutionary cognition instead.

Psychologists often assume that there is a special cognitive ability—a psychological secret sauce—that makes humans different from other animals. The list of candidates is long: tool use, cultural transmission, the ability to imagine the future or to understand other minds, and so on. But every one of these abilities shows up in at least some other species in at least some form. De Waal points out various examples, and there are many more. New Caledonian crows make elaborate tools, shaping branches into pointed, barbed termite-extraction devices. A few Japanese macaques learned to wash sweet potatoes and even to dip them in the sea to make them more salty, and passed that technique on to subsequent generations. Western scrub jays “cache”—they hide food for later use—and studies have shown that they anticipate what they will need in the future, rather than acting on what they need now.

From an evolutionary perspective, it makes sense that these human abilities also appear in other species. After all, the whole point of natural selection is that small variations among existing organisms can eventually give rise to new species. Our hands and hips and those of our primate relatives gradually diverged from the hands and hips of common ancestors. It’s not that we miraculously grew hands and hips and other animals didn’t. So why would we alone possess some distinctive cognitive skill that no other species has in any form?

De Waal explicitly rejects the idea that there is some hierarchy of cognitive abilities. Nevertheless, an implicit tension in his book shows just how seductive the ladder-of-nature view remains. Simply saying that the “lower” creatures share abilities with creatures once considered more advanced still suggests something like a ladder—it’s just that chimps or crows or children are higher up than we thought. So the summary of the research ends up being: We used to think that only adult humans could use tools/participate in culture/imagine the future/understand other minds, but actually chimpanzees/crows/toddlers can too. Much of de Waal’s book has this flavor, though I can’t really blame him, since developmental psychologists like me have been guilty of the same rhetoric.

As de Waal recognizes, a better way to think about other creatures would be to ask ourselves how different species have developed different kinds of minds to solve different adaptive problems. Surely the important question is not whether an octopus or a crow can do the same things a human can, but how those animals solve the cognitive problems they face, like how to imitate the sea floor or make a tool with their beak. Children and chimps and crows and octopuses are ultimately so interesting not because they are mini-mes, but because they are aliens—not because they are smart like us, but because they are smart in ways we haven’t even considered. All children, for example, pretend with a zeal that seems positively crazy; if we saw a grown-up act like every 3-year-old does, we would get him to check his meds.

Sometimes studying those alien ways of knowing can illuminate adult-human cognition. Children’s pretend play may help us understand our adult taste for fiction. De Waal’s research provides another compelling example. We human beings tend to think that our social relationships are rooted in our perceptions, beliefs, and desires, and our understanding of the perceptions, beliefs, and desires of others—what psychologists call our “theory of mind.” In the ’80s and ’90s, developmental psychologists, including me, showed that preschoolers and even infants understand minds apart from their own. But it was hard to show that other animals did the same. “Theory of mind” became a candidate for the special, uniquely human trick.

Yet de Waal’s studies show that chimps possess a remarkably developed political intelligence—they are profoundly interested in figuring out social relationships such as status and alliances. (A primatologist friend told me that even before they could stand, the baby chimps he studied would use dominance displays to try to intimidate one another.) It turns out, as de Waal describes, that chimps do infer something about what other chimps see. But experimental studies also suggest that this happens only in a competitive political context. The evolutionary anthropologist Brian Hare and his colleagues gave a subordinate chimp a choice between pieces of food that a dominant chimp had seen hidden and other pieces it had not seen hidden. The subordinate chimp, who watched all the hiding, stayed away from the food the dominant chimp had seen, but took the food it hadn’t seen.

Anyone who has gone to an academic conference will recognize that we, too, are profoundly political creatures. We may say that we sign up because we’re eager to find out what our fellow Homo sapiens think, but we’re just as interested in who’s on top and where the alliances lie. Many of the political judgments we make there don’t have much to do with our theory of mind. We may defer to a celebrity-academic silverback even if we have no respect for his ideas. In Jane Austen, Elizabeth Bennet cares how people think, while Lady Catherine cares only about how powerful they are, but both characters are equally smart and equally human.

Of course, we know that humans are political, but we still often assume that our political actions come from thinking about beliefs and desires. Even in election season we assume that voters figure out who will enact the policies they want, and we’re surprised when it turns out that they care more about who belongs to their group or who is the top dog. The chimps may give us an insight into a kind of sophisticated and abstract social cognition that is very different from theory of mind—an intuitive sociology rather than an intuitive psychology.

Until recently, however, there wasn’t much research into how humans develop and deploy this kind of political knowledge—a domain where other animals may be more cognitively attuned than we are. It may be that we understand the social world in terms of dominance and alliance, like chimps, but we’re just not usually as politically motivated as they are. Instead of asking whether we have a better everyday theory of mind, we might wonder whether they have a better everyday theory of politics.

Thinking seriously about evolutionary cognition may also help us stop looking for a single magic ingredient that explains how human intelligence emerged. De Waal’s book inevitably raises a puzzling question. After all, I’m a modern adult human being, writing this essay surrounded by furniture, books, computers, art, and music—I really do live in a world that is profoundly different from the world of the most brilliant of bonobos. If primates have the same cognitive capacities we do, where do those differences come from?

The old evolutionary-psychology movement argued that we had very specific “modules,” special mental devices, that other primates didn’t have. But it’s far likelier that humans and other primates started out with relatively minor variations in more-general endowments and that those variations have been amplified over the millennia by feedback processes. For example, small initial differences in what biologists call “life history” can have big cumulative effects. Humans have a much longer childhood than other primates do. Young chimps gather as much food as they consume by the time they’re 5. Even in forager societies, human kids don’t do that until they’re 15. This makes being a human parent especially demanding. But it also gives human children much more time to learn—in particular, to learn from the previous generation. Other animals can absorb culture from their forebears too, like those macaques with their proto-Pringle salty potatoes. But they may have less opportunity and motivation to exercise these abilities than we do.

Even if the differences between us and our nearest animal relatives are quantitative rather than qualitative—a matter of dialing up some cognitive capacities and downplaying others—they can have a dramatic impact overall. A small variation in how much you rely on theory of mind to understand others as opposed to relying on a theory of status and alliances can exert a large influence in the long run of biological and cultural evolution.

Finally, de Waal’s book prompts some interesting questions about how emotion and reason mix in the scientific enterprise. The quest to understand the minds of animals and children has been a remarkable scientific success story. It inevitably has a moral, and even political, dimension as well. The challenge of studying creatures that are so different from us is to get into their heads, to imagine what it is like to be a bat or a bonobo or a baby. A tremendous amount of sheer scientific ingenuity is required to figure out how to ask animals or children what they think in their language instead of in ours.

At the same time, it also helps to have a sympathy for the creatures you study, a feeling that is not far removed from love. And this sympathy is bound to lead to indignation when those creatures are dismissed or diminished. That response certainly seems justified when you consider the havoc that the ladder-of-nature picture has wrought on the “lower” creatures.

But does love lead us to the most-profound insights about another being, or the most-profound illusions? Elizabeth Bennet and Lady Catherine would have differed on that too, and despite all our theory-of-mind brilliance, we humans have yet to figure out when love enlightens and when it leads us astray. So we keep these emotions under wraps in our scientific papers, for good reason. Still, popular books are different, and both sympathy and indignation are in abundant supply in de Waal’s.

Perhaps the combination of scientific research and moral sentiment can point us to a different metaphor for our place in nature. Instead of a ladder, we could invoke the 19th-century naturalist Alexander von Humboldt’s web of life. We humans aren’t precariously balanced on the top rung looking down at the rest. It’s more scientifically accurate, and more morally appealing, to say that we are just one strand in an intricate network of living things.