Late one evening in the summer of 2012, a group of researchers stood outside a bar in Lawrence, Kansas. They worked for Laura Van Berkel, a graduate student in psychology at the University of Kansas who was interested in how drinking alcohol affects people’s thinking about equality. To that end, as people left the bar, the researchers asked them questions and measured their blood-alcohol levels. (For example, the drinkers were asked to rate, on a nine-point scale, the importance of “control or dominance over people or resources” as a “guiding principle in your life.”) The researchers’ hunch was that it takes mental effort to overcome hierarchical thinking—and that, as a result, drunk people, who are cognitively impaired, might have trouble thinking in egalitarian ways.

According to a 2009 review, conservatives tend to support hierarchy and authority more than liberals do. Van Berkel, working with Chris Crandall and other colleagues, found that, in terms of how the hundred and seven subjects interviewed outside the bar thought about hierarchy, drunk people gave more conservative responses while sober people gave more liberal ones. Over the next few years, she and her team ran five more experiments, exploring the relationship between mental effort and support for hierarchy. In each case, they found that cognitive impairments, such as being stressed or distracted, made people more likely to favor hierarchy. Even encouraging “low-effort thought”—by forcing respondents to think quickly, say—made people more respectful of those in charge.

Van Berkel’s research is part of a larger effort to understand how hierarchy fits into our mental lives. Her findings suggest that, in many situations, hierarchical thinking is the default; when we don’t have the time, energy, inclination, or capacity to think carefully, we fall back on the notion that we should honor those with more power and prestige. If she’s right, she’s identified a tendency with everyday consequences. For instance, when we’re under time pressure at work, we might be less likely to listen to all ideas equally, and more likely to align ourselves with the most powerful person present. On the flip side, Van Berkel’s work illuminates the mental conditions in which equality might flourish. When we can think clearly and at leisure, we are more likely to do so through the lens of equality.

These findings give us an interesting way to think about equality—as the product of a state of mind. But that’s only part of the picture. While psychologists tend to conceptualize people as individuals, we are also social beings, and the social environments in which we find ourselves shape our mental states. Think of how the same person may act very differently at a bar, in a job interview, and during a church sermon. The person in question doesn’t have a personality disorder; the social demands of the situation are different, and she acts accordingly. Another way, therefore, to investigate how people think about equality and hierarchy is to ask which social situations lead us to champion one over the other.

Christopher Boehm, a cultural anthropologist at the University of Southern California, has approached this question from a cross-species angle. Boehm, who directs the Jane Goodall Research Center, has spent his career studying human and primate communities. In 1999, he published a now classic book, “Hierarchy in the Forest,” which compares human hunter-gatherer and tribal societies to those of bonobos, chimpanzees, and gorillas. Boehm reports that our closest evolutionary relatives are far more hierarchical than we are: the dominance of the powerful in chimpanzee society, for example, is unlike anything we see among humans. Why, he asks, do tribal and hunter-gatherer human societies tend to be more equal?

One possible answer is that human beings are, at the level of personality, more egalitarian than apes. But Boehm doesn’t find much evidence for this idea: he points out that most people, like most chimpanzees, want power and dislike being dominated. It’s also not the case that tribal human societies are organized in some fundamentally different and more egalitarian fashion. At a basic level, the social structures of human and chimp societies are the same—they are pyramidal societies in which only one person (or a very small group of people) can occupy the top position.

All primate societies, Boehm notes, are governed by similar dynamics. If any one individual has the opportunity to climb the hierarchy, he or she is likely to seize it; unfortunately, as soon as power is gained, others resent it. In such a society, Boehm writes, there are three potential outcomes. One is conflict, in which newcomers continually and overtly challenge the powerful for a position at the top. Another is stable dominance, where the powerful relentlessly and permanently dominate the rest. And a third is an equally stable social structure which Boehm calls “reverse dominance hierarchy,” in which those on the bottom of the pyramid figure out a way to band together and “deliberately dominate their potential master.” In such a society, dominance is still exercised. It just comes, collectively and consistently, from below.

Chimps, bonobos, and gorillas struggle to achieve stable reverse-dominance hierarchy. They can occasionally flatten their pyramids, but only briefly. The problem is that the powerful are likely to be strong, intelligent, and socially connected. To topple them, and prevent them from taking over again, you need a powerful and persistent threat, which nonhuman primates don’t have. Boehm has discovered that, among the tribal and hunter-gatherer human societies he studies, the development of projectile weapons is a key step in the growth and maintenance of equality: it puts the strong at greater risk from the weak. Such weaponry is one reason that human societies are more equalized than those of other primates.

But weapons aren’t enough to make equality last. Boehm finds that, to really maintain the new social order, the dominated need to trust one another. They must have stable social bonds and anticipate a long future together. Most important, they must be able to communicate effectively. To Boehm, therefore, there is something distinctively human about sustained equality: only human beings communicate well enough to keep it going for long periods. Van Berkel, for her part, suggests that we default to hierarchical models for developmental reasons, since respect for authority is what we learn first. But it’s also possible to read her findings in a humanistic way: deferring to authority could be a tendency that honors our less deliberative, more animalistic selves.

Unfortunately, when it’s seen through the lens of Van Berkel and Boehm’s work, our contemporary society seems to encourage us to stick with the default setting of hierarchy. We now know that poor people experience cognitive exhaustion, because they are constantly preoccupied by money, food, housing, and other basics of survival; meanwhile, the well-off distract themselves with smartphones. To the extent that Van Berkel’s work suggests that we need calm and clear minds to think liberally about equality, it’s plausible that our fast-paced, distracting world is encouraging us to fall back on hierarchical thinking. Meanwhile, although Boehm’s work identifies trust, communication, and a collective belief that we have a future together as social factors on which long-term equality depends, the modern era has enabled increasingly polarized and individualistic behaviors for many of us.

In a broad sense, this research gives us a picture of how dominance, in the abstract, works to sustain itself. If you’re at the top of a very hierarchical society and are absolutely determined to stay there, then you want three things. First, you want people to fear your power, so that they’re unwilling to risk toppling you. Second, you want to occupy people’s minds—and potentially, their bodies—so thoroughly that they’re mentally exhausted and oriented more toward hierarchy and authority than toward equality and justice. Finally, you want to make sure that those you dominate are unable to meaningfully communicate—or that, if they can, they are loath to trust one another in the long run. Division is your ally. Power wants the powerless to be scared, thoughtless, and alone.