The “intoxication thesis”: The evolutionary benefits of getting drunk

“The classic example of a hijack is masturbation,” Edward Slingerland tells me. We’re talking about all the evolutionary quirks that humans tend to exploit — the cases where we’re “built” for one purpose, but decide to put that structure to other uses. And masturbation is a classic example.

In this week’s Mini Philosophy interview, I spoke with Slingerland about his book Drunk, in which he outlines his “intoxication thesis.” Slingerland argues it’s quite common to think that getting drunk is an evolutionary mistake. Some early Homo sapiens drank too much fermented fruit juice and discovered it was pretty fun. So they told their mates and, altogether, they clinked their frothy ciders and sang bawdy songs about hunting and gathering. But the human brain and body were not built to get drunk. Alcohol is effectively a poison. Our bodies don’t like it — or so the argument goes.

The intoxication thesis says this is all wrong. For Slingerland, drinking alcohol and getting drunk are important to human well-being and complex societies. It might not be what evolution “intended,” but it’s certainly given us a reproductive and interspecies advantage.

So, how is getting drunk different from other “evolutionary mistakes”? And what possible benefits might getting drunk give us? Today, we find out.

The classic example

The reason that masturbation is the “classic example” of an evolutionary mistake is that there’s a very obvious and simple answer as to why an orgasm feels great — it is nature’s reward for doing what our genes really “want” us to do: copy themselves into the next generation. This is what evolutionary biologists call the “adaptive target” of the orgasm. Have sex, reproduce, copy your genes, and you’ll get this surge of dopamine, oxytocin, and lovely, lovely endorphins.

“But humans and other animals have figured out you can get that reward in lots of wildly non-reproductive ways,” Slingerland tells me. “And once we figured that out, we did that all the time. So here’s the classic ‘mistake,’ right: There’s no relationship between an orgasm and reproduction. Evolution doesn’t want us to masturbate, but it doesn’t care because it’s a relatively non-costly behavior. Contrary to what you may have learned in school, it won’t make you go blind. It’s basically low-cost enough that evolution can kind of let it go.”

In other words, from an evolutionary point of view, the cost of masturbation and hijacking the pleasure surge of an orgasm is worth it, so long as humans do, at least a few times, still have an orgasm during reproductive sex.

The Twinkie problem

The other kind of evolutionary mistake is what Slingerland calls the “Twinkie problem,” which is when the body’s reward system was once connected to a certain evolutionarily beneficial behavior, but our environment has now changed so much that the reward system is actually detrimental to our well-being. This is how Slingerland describes it:

“We’re evolutionarily designed to enjoy fat and sugar. We’ll consume it in large quantities whenever we can get it. And that’s great because for almost all of our evolutionary history, and actually for a disturbing number of people still today, getting enough sugar and fat is a problem. And so, you should try to gorge on it whenever you get it. But it becomes a problem when you live in a modern industrialized society and you’re relatively wealthy. You can gorge on Twinkies and potato chips and ice cream.

So, this type of mistake is costly because it causes obesity, diabetes, and all these problems, but it’s very recent, evolutionarily, and it’s geographically still constrained. Again, there are places in the world where you still have trouble getting enough food.”

In other words, while the Twinkie problem is a problem for a growing portion of society, it’s not enough of a problem to fade away — not least because the time scale’s too short for any kind of adaptation. Maybe, in the future, diabetes and obesity will kill off those who really enjoy fat and sugar, and so change the reward system. But that’d be in the far distant future.

The benefits of alcohol

The traditional view of alcohol is to see it like masturbation. It’s a mistake that only a few abuse, and so evolution has no “need” to get rid of our enjoyment of getting drunk. We have a reward system, and we’ve realized we can trigger it by drinking this fermented fruit juice. We’re like rats pushing the button to get more cocaine.

But Slingerland’s intoxication thesis argues that this cannot be true “because our taste for alcohol is ancient and ubiquitous and costly. Evolution doesn’t let that kind of mistake slide. And so, getting drunk has got to have a benefit that’s kept it in our repertoire.”

Slingerland’s book explores what he considers to be a range of benefits, but in our interview, we focused mostly on two:

First, there is a social aspect to getting drunk. When we drink with someone, we not only have the bonding experience of mutual enjoyment, but also come together in mutual vulnerability. When you are drunk, you’re easy to kill. When you’re staggering home, narrowly avoiding lampposts, it’s easy to steal your phone, your wallet, and your jacket. To be drunk with someone is an act of trust. It says, “I think so much of you that I’m willing to let my guard down.” And so, getting drunk is a kind of “chemical handshake” that lets the other person know you are someone to trust. Societies operate on trust, and alcohol is a kind of “social technology” that builds trust between potentially warring rivals.

Second, there is the creative aspect of being drunk. This isn’t (just) about Lennon and McCartney getting high and writing “Strawberry Fields Forever”; this is about the thinking-outside-the-box skills we need to survive and thrive. This is how Slingerland put it:

“So, one of the main functions of alcohol is to depress selectively the prefrontal cortex (PFC). It turns the PFC down a few notches and helps us get back to that childlike state of mind where suddenly we see connections we wouldn’t see otherwise. Parts of our brain can talk to each other in ways that they don’t when the PFC is in charge.

And so, let’s say you sit down and you need to come up with a new idea. You have a couple of drinks. You are individually more creative because your brain is now de-patterned in a certain way. Plus, because you’re disinhibited—again, because the PFC has been turned down—you’re more likely to blurt out something to someone else that maybe you would be self-conscious about, or maybe you think it is a dumb idea. You’ll suddenly be like, well, why don’t we try this for getting gazelles?”

Taken together, Slingerland’s argument is that our so-called “evolutionary mistakes” often reveal evolution’s hidden genius. Masturbation, sugar binges, and drunken nights look like misfires in nature’s design—but they’ve helped us adapt. We’ve taken reward systems meant for survival and reproduction and retooled them for connection, innovation, and joy.