What the study really illustrated, then, was a paradox: when it comes to information, sharing is mostly about me. The researchers weren’t trying to answer the thornier question of why—why, as they wrote, our species might have “an intrinsic drive to disclose thoughts to others.” The paper nonetheless points to an intriguing possibility: that this drive might give us humans an adaptive advantage.

Researchers have previously shown that certain online activities—such as checking your e-mail or Twitter stream—stimulate the brain’s reward system. Like playing a slot machine, engaging in these activities sends the animal brain into a frenzy as it anticipates a possible reward: often nothing, but sometimes a small prize, and occasionally an enormous jackpot. The response to this unpredictable pattern seems to be deeply ingrained, and for the most basic of reasons: precisely the same cycle of suspense and excitement motivates animals to keep hunting for food. E-mail inboxes and slot machines simply tap into an attention-focusing mechanism that’s perfectly designed to make sure we don’t lose interest in Job No. 1, which is to keep ourselves alive.

However unrelated food and Facebook may seem, this foraging impulse sheds light on why, by one count, 96 percent of the country’s online population uses social-­networking sites: we get high from being on the receiving end of social media. But that’s only half the story. The Harvard study helps clarify why we are so eager to be on the sharing side as well. “This would certainly explain the barroom bore, wouldn’t it?” said Brian Boyd, the author of the literary Darwinist treatise On the Origin of Stories, when I asked him about the brain’s response to acts of self-­disclosure. What about estimates that, while 30 to 40 percent of ordinary conversation consists of people talking about themselves, some 80 percent of social-media updates fall in the same category? “Ordinarily, in a social context, we get feedback from other people,” Boyd told me. “They might roll their eyes to indicate they don’t want to hear so much about us. But online, you don’t have that.”

At first blush, the notion that the self-disclosure impulse is somehow good for the species might seem counterintuitive. If all we did was prattle on about ourselves, we’d soon bore one another to extinction. Why would we have evolved to get a rush of pleasure from hearing ourselves talk?

A closer look at the advantages conferred by storytelling offers some clues: by telling stories effectively, we gain status, obtain social feedback, and strengthen our bonds with other people. And on the flip side, all of this nattering—­or tweeting—by our fellow humans ensures that we don’t have to discover everything on our own. We have no end of people competing to tell us what’s what. Hence the real paradox of sharing: what feels good for me probably ends up benefiting us all.