Roughly 6 million years ago, our ancestors migrated from the dense rainforest to the open savannah in East Africa. It was one of the most significant events in the history of human evolution.

Life on the sprawling grasslands precipitated a shift from individualistic ways of living to more cooperative ways. This was the birth of what you might call “social intelligence,” and it changed the way our minds work forever.

It explains why our psychological health depends so heavily on our status within a particular social group. It even explains why we love to exaggerate and why we’re so good at believing each other’s bullshit.

This is the argument psychology professor William von Hippel makes in his fascinating new book The Social Leap. According to von Hippel, the move from the rainforest to the savannah produced a cascade of advances in human intelligence and innovation that led inexorably to the world we live in today. But it also cemented pathologies in the human mind that continue to shape how we live, think, and judge.

I spoke with von Hippel about the significance of the “social leap” and why he believes this mostly overlooked part of human history explains so many of our psychological quirks.

A lightly edited transcript of our conversation follows.

Sean Illing

Your book is obviously about the past, but it has just as much to say about the present, about why human beings are so strange and self-destructive. Why tell this story now?

William von Hippel

I’m really interested in social intelligence. I want to know what makes people socially successful. And I’ve been trying to work that out for a long time, with limited success. So I started to think, well, maybe the better way to understand this problem is not to look at where we are now, but instead to look at where we came from.

So I became really interested in looking at our history as we separated from chimpanzees, because we’re so different from them socially. What caused that separation? What were they key events that occurred along the way? And can those events give us any purchase on understanding our social situation now?

“Humans are social animals, and if our group will benefit from seeing the world a certain way, we’ll use our intelligence to see the world that way”

Sean Illing

And what did you find? What did this history explain about the human psyche today?

William von Hippel

Well, I think it tells us a couple of very important things. Perhaps the most important thing is that what got us going, as a species, was when we came together to cooperate in our mutual defense on the East African savanna. This happened 3.5 million years ago, and it probably happened because our ancestors had to protect themselves against large predators like lions and leopards.

The consequences of this were profound for how we lived and how our minds worked. Suddenly, we were much more successful when our group goals aligned with our individual goals, which is, in this particular case, cooperation for mutual defense. But it also mandated a massive change in our psychology. Chimpanzees do not cooperate very well. And so we had to change the way we oriented toward the world.

Now, that tells us several important things. First, it’s weird that we’re both really kind to each other and also really, really mean to each other. But it actually makes perfect sense if you think about the fact that we evolved our cooperative nature in order to become more effective killers.

Important thing number two: This is also when our brain power really kicked into gear. Prior to this, we’d gained very little cognitive expansion from chimpanzees. We’d gained 70 grams of brain over 3 million years. And since then, we’ve almost tripled our brain size.

Why did that happen? Well, living together in large groups presented all sorts of challenges that had to be solved, and in solving them, we had to become more sophisticated, more intelligent, more innovative.

What that tells me is that, really, our intelligence didn’t evolve to solve abstract problems and complex ways of dealing with the environment. Our intelligence evolved to deal with each other more effectively and to leverage the skills and abilities we have when we work together.

Sean Illing

You spend a lot of time in the book talking about our primordial fear of being ostracized from our social group. Why is that such a big deal and an essential part of our psychology, even today?

William von Hippel

I recently read a great interview you did with a Stanford psychologist about how to avoid assholes. His advice was basically to not care what people think.

But that’s a stunningly difficult piece of advice to follow, because we’ve evolved to care a great deal about what everyone else in our group is thinking and about what everyone else in our group is doing. Because that’s what made us so effective.

And, simultaneously, because our groups have historically been so essential to keeping us alive, getting tossed out of them was often a death sentence for us.

So it’s not so easy to avoid worrying about what other people are thinking, or to not worry about being rejected. We’re simply hardwired to care deeply about what other people are thinking, whether it’s on the African savannah a few million years ago or on Twitter today — it matters a ton to us.

Sean Illing

This helps explain why we love gossip so much, right?

William von Hippel

Absolutely! It’s sort of the strength and weakness of humans. If you look back at our ancestral environment, we were in each other’s business all the time, and we regulated people’s behavior via gossip and what you might call “reputation management.” It was really, really important.

So gossip might be trivial and salacious in many ways, but it’s also super important for humans to make sure they’re all on the same page and get their group going in the right direction.

I think we’ve returned to this ancestral environment with the internet. People use social media to judge each other, to punish and reward, to regulate behavior. And the problem is that when all those people pile on you, it can be devastating because we’ve evolved in an environment in which having 20 people pile on you might have been a death sentence.

The stakes have obviously changed, but this stuff is still very much a part of our psychology, and it’s important to remember that.

Sean Illing

We have to talk about the role of reason in human life. According to your account, human intelligence evolved for strictly social purposes, and we developed our reasoning capacities as a means of manipulating our social environment, not necessarily as a tool for understanding how the world works.

Why is this so important?

William von Hippel

Well, the implications are hugely important. If we evolved to be smart in order to facilitate social functioning, then part of our smarts definitely will be dedicated to understanding the world, because you need some vague understanding of what’s actually out there in order to function.

But most of our smarts are going be dedicated to jockeying and manipulating our position among others. And if that’s the case, then the truth is only semi-important. If I can convince you of a world that’s actually favorable to me, then I can get you to back down in conflicts or defer to me when you really shouldn’t; that is a form of power.

So what are some other implications? Well, one is that we tend to think that the smarter we are, the more capable we are of seeing through people’s lies and the more capable we are of finding the truth. But that’s absolutely not the case. Humans are social animals, and if our group will benefit from seeing the world a certain way, we’ll use our intelligence to see the world that way.

It’s easy to see how these impulses explain so much of our politics and how willing so many of us are to believe what is false but convenient, as opposed to what is true but inconvenient. I think it also explains why the internet has not made us more intellectually honest; instead, people are just better at finding the information they need to confirm what they need to be true, which is what we’ve always done.

Sean Illing

Tell me how these group dynamics explain why we love to bullshit each other so much.

William von Hippel

We evolved in ways that forced us to come to an agreement about the facts within our groups. In other words, we needed to be on the same page about what’s going on, and we needed to share an emotional response to that reality.

Now, that means it’s very upsetting to me if you don’t share my emotional response to the world, and one of us has to change. One way I can ensure that you share my emotional response is to exaggerate my claims about the world. So if I need you to be outraged about something, it’s in my interest to exaggerate in ways that are more likely to outrage you, or whatever the case may be. The key is that we share an emotional response and forge a bond with one another.

This is how groups became tighter, and I think it’s the source of nearly all exaggeration. Why else would we lie about what happened or what’s happening? Ultimately, it’s about manipulating other people’s emotions.

Sean Illing

Cooperation is coded into our mental software and is a big reason for our success as a species, yet modern Western culture is essentially a sustained effort to individualize us. Is this a contradiction we can live with forever?

William von Hippel

That’s a terrific question, and it’s hard to answer. We’re all struggling with the tension between autonomy and connectedness. All humans want to have some level of self-directedness. We want to pursue our goals and dreams. And at the same time, all humans want to be connected to others. We want to maintain important relationships.

These two fundamental goals almost never mesh perfectly. And what’s interesting is if you look at the history of the world, people historically have been way more connected to each other with very little autonomy. As culture becomes more Westernized or industrialized or urbanized or whatever term you want to use, it shifts from a more collectivist culture to a more individualistic culture.

What that tells me is that at an individual level, all of us, when we’re in these tight and interconnected communities, have a strong desire for autonomy. But then when we get too much autonomy, we often miss that small town we grew up in or miss the connections we had with the people around us.

This is a contradiction we just have to live with now, and I’d be lying if I told you I knew how it was all going to play out in the future.