What drives human behavior? Why do we do what we do? Is free will an illusion? Has civilization made us better? Can we escape our tribal past?

These questions (and many, many others) are the subject of a new book called Behave: The Biology of Humans at Our Best and Worst. The author is Robert Sapolsky, a biology professor at Stanford and a research associate with the Institute of Primate Research at the National Museums of Kenya.

In a brisk 800 pages, Sapolsky covers nearly every facet of the human condition, engaging moral philosophy, evolutionary biology, social science, and genetics along the way.

The key question of the book — why are we the way we are? — is explored from a multitude of angles, and the narrative structure helps guide the reader. For instance, Sapolsky begins by examining a person’s behavior in the moment (why we recoil or rejoice or respond aggressively to immediate stimuli) and then zooms backward in time, following the chain of antecedent causes back to our evolutionary roots.

For every action, Sapolsky shows, there are several layers of causal significance: There’s a neurobiological cause and a hormonal cause and a chemical cause and a genetic cause, and, of course, there are always environmental and historical factors. He synthesizes the research across these disciplines into a coherent, readable whole.

In this interview, I talk with Sapolsky about the paradoxes of human nature, why we’re capable of both good and evil, whether free will exists, and why symbols have become so central to human life.

This conversation has been edited for length and clarity.

The paradox of human nature

Sean Illing

You start the book with a paradox of sorts: Humans are both exceptionally violent and exceptionally kind. We’re capable on the one hand of mass genocide, and on the other hand of heroic self-sacrifice. How do we make sense of this dichotomy?

Robert Sapolsky

In an evolutionary sense, we're this incredibly confused species, in between all sorts of extremes of behavior and patterns of selection compared to other primates who are far more consistently X or Y, and we're so often floating in between. In a more proximal sense, I think what that tells you over and over again is just how important context is.

Sean Illing

Can you clarify what you mean by context here?

Robert Sapolsky

Sure. What counts as our worst and best behaviors are so much in the eye of the beholder. So often it really is the one man's freedom fighter versus the other's terrorist. But even separate of that, just the fact that in some settings our biology is such that we are extraordinarily prosocial creatures, and in other settings extraordinarily antisocial creatures, shows how important it is to really understand the biology of our response to context and environment.

Sean Illing

You argue that biological factors don't so much cause behavior as modulate it — can you explain what you mean?

Robert Sapolsky

Ultimately, there is no debate. Insofar as using "genes" as a surrogate for "nature," it only makes sense to ask what a gene does in a particular environment, and to ask what the behavioral effects of an environment are given someone's genetic makeup. They're inseparable in a way that is most meaningful when it comes to humans.

Sean Illing

Given how variable human behavior is, do you believe in a fixed human nature? There is a lot of debate about this in the world of philosophy. I wonder how you think about it as a scientist.

Robert Sapolsky

Human nature is extraordinarily malleable, and I think that's the most defining thing about our nature.

Free will is an illusion

Sean Illing

Okay, but in the book you come awfully close to concluding something very different. Specifically, in your discussion of free will, you reluctantly embrace a deterministic account of human behavior. You argue that free will is, in fact, an illusion, and if that’s true, I’m not sure how “malleable” we can be.

Robert Sapolsky

If it seemed tentative, it was just because I was trying to be polite to the reader or to a certain subset of readers. If there is free will, it’s free will about all sorts of uninteresting stuff, and it's getting cramped into tighter and increasingly boring places. It seems impossible to view the full range of influences on our behavior and conclude that there is anything like free will.

Sean Illing

That’s a bold claim...

Robert Sapolsky

You’re right. On the one hand, it seems obvious to me and to most scientists thinking about behavior that there is no free will. And yet it’s staggeringly difficult to try to begin to even imagine what a world is supposed to look like in which everybody recognizes this and accepts this.

The most obvious place to start is to approach this differently in terms of how we judge behavior. Even an extremely trivial decision like the shirt you choose to wear today, if dissected close enough, doesn’t really involve agency in the way we assume. There are millions of antecedent causes that led you to choose that shirt, and you had no control over them. So if I was to compliment you and say, “Hey, nice shirt,” that doesn’t really make any sense in that you aren’t really responsible for wearing it, at least not in the way that question implies.

Now, this is a very trivial thing and doesn’t appear to matter much, but this logic is also true for serious and consequential behaviors, and that’s where things get complicated.

Sean Illing

If we're just marionettes on a string and we don't have the kind of agency that we think we have, then what sense does it make to reward or punish behavior? Doesn’t that imply some degree of freedom of action?

Robert Sapolsky

Organisms on the average tend to increase the frequency of behaviors for which they’ve been rewarded and to do the opposite for punishment or absence of reward. That's fine and instrumentally is going to be helpful in all sorts of circumstances. The notion of there being something virtuous about punishing a bad behavior, that's the idea that’s got to go out the window.

I always come back to the example of epilepsy. Five hundred years ago, an epileptic seizure was a sign that you were hanging out with Satan, and the appropriate treatment for that was obvious: burning someone at the stake. This went on for hundreds of years. Now, of course, we know that such a person has got screwy potassium channels in their neurons. It's not them; it's a disease. It's not a moral failing; it's a biological phenomenon.

Now we don’t punish epileptics for their epilepsy, but if they suffer bouts frequently, we might not let them drive a car because it’s not safe. It’s not that they don’t deserve to drive a car; it’s that it’s not safe. It’s a biological thing that has to be constrained because it represents a danger.

It’s taken us 500 years or so to get to this revelation, so I don’t know how long it will take us to reach this mindset for all other sorts of behaviors, but we absolutely must get there.

Sean Illing

So what is true for the epileptic is true for all of us all of the time? We are our brains and we had no role in the shaping of our biology or our neurology or our chemistry, and yet these are the forces that determine our behavior.

Robert Sapolsky

That’s true, but it’s still difficult to fully grasp this. Look, I believe there is no free will whatsoever, but I can't function that way. I get pissed off at our dog if he pees on the floor in the kitchen, even though I can easily come up with a mechanistic explanation for that.

Sean Illing

Our entire notion of moral and legal responsibility is thrown into doubt the minute we fully embrace this truth, so I’m not sure we can really afford to own up to the implications of free will being an illusion.

Robert Sapolsky

I think that’s mostly right. As individuals and a society, I’m not sure we’re ready to face this fact. But we could perhaps do it bits and pieces at a time.

“Our species has problems with violence”

Sean Illing

You write that “our species has problems with violence.” Can you explain this complicated relationship?

Robert Sapolsky

The easiest answer is that we're really violent. The much more important one, the much more challenging one, is that we don't hate violence as such — we hate the wrong kind of violence, and when it's the right kind of violence, we absolutely do cartwheels to reinforce it and reward it and hand out medals and mate with such people because of it. And that’s part of the reason why the worst kinds of violence are so viscerally awful to experience, to bear witness to. But the right kinds of violence are just as visceral, only in the opposite direction.

The truth is that this is the hardest realm of human behavior to understand, but it’s also the most important one to try to.

Sean Illing

What is the wrong kind of violence? What is the right kind of violence?

Robert Sapolsky

Of course that tends to be in the eye of the beholder. Far too often, the right kind is one that fosters the fortunes of people just like us in group favoritism, and the worst kinds are the ones that do the opposite.

Sean Illing

Violence is a fact of nature — all species engage in it one way or other. Are humans the only species that ritualizes it, that makes a sport of it?

Robert Sapolsky

That does seem pretty much the case. Certainly you see the hints of it in chimps, for example, where you see order patrols by male chimps in one group, where if they encounter a male from another group, they will kill him. They have now been shown in a number of circumstances to have systematically killed all the males in the neighboring group, which certainly fits a rough definition of genocide, which is to say killing an individual not because of what they did but simply because of what group they belong to.

What's striking with the chimps is that you can tell beforehand that this is where they are heading. They do something vaguely ritualistic, which is they do a whole bunch of emotional contagion stuff. One male gets very agitated, very aroused, manages to get others like that, and then off they go to look for somebody to attack. So in that regard, there is a ritualistic feel to it, but that's easily framed along the conventional lines of nonhuman animal violence. By that, I mean when male chimps do this, when they eradicate all of the other males in a neighboring territory, they expand their own; it increases their reproductive success.

I believe it is really only humans that do violence for purely ritualistic purposes.

Humans are tribal animals

Sean Illing

Is our tribal past the most important thing to understand about human behavior?

Robert Sapolsky

I think it's an incredibly important one, and what's most important about it is to understand the implications of the fact that all of us have multiple tribal affiliations that we carry in our heads and to understand the circumstances that bring one of those affiliations to the forefront over another. The mere fact that you can switch people's categorization of others from race to religion to what sports team they follow speaks to how incredibly complicated and central tribal affiliation is to humans and to human life.

Sean Illing

You spend a lot of time talking about the role of symbols and ideas in human life. We kill and we die for our symbols, and we often confuse the symbols themselves for the things they symbolize. Do you think symbols and ideas amplify our tribal nature, or do they help us transcend it?

Robert Sapolsky

Well, it’s important to understand that not only are we willing to kill people because they look, dress, eat things, smell, speak, sing, pray differently from us, but also because they have incredibly different ideas as to very abstract notions. I think the thing that fuels that capacity is how primitively our brains do symbolism.

I think the fact that our brains so readily intermix the abstractions and symbols with their visceral, metaphorical analogues gives those abstractions and symbols enormous power. That fact that we’re willing to kill and die for abstract symbols is itself crazy, but nonetheless true.

Reasons for optimism

Sean Illing

Has civilization made us better?

Robert Sapolsky

Absolutely. The big question is which of the following two scenarios are more correct: a) Civilization has made us the most peaceful, cooperative, emphatic we've ever been as a species, versus b) civilization is finally inching us back to the level of all those good things that characterized most of hominin hunter-gatherer history, preceding the invention of agriculture. Amid mostly being an academic outsider to the huge debates over this one, I find the latter view much more convincing.

Sean Illing

You say you incline to pessimism but that this book gave you reasons to be optimistic. Why?

Robert Sapolsky

Because there's very little about our behaviors that are inevitable, including our worst behaviors. And we’re learning more and more about the biological underpinnings of our behavior, and that can help us produce better outcomes. As long as you have a ridiculously long view of things, things are getting better.

It’s much nicer to be alive today than it was 100 or 200 years ago, and that’s because we’ve progressed. But nothing is certain, and we have to continue moving forward if we want to preserve what progress we’ve made.