Key Takeaways

  • Contrary to popular belief, genetic selection for traits tied to cognitive performance and 'years of schooling' was strongest during the Bronze Age (5,000-2,000 years ago).
  • In the last 2,000 years, the genetic impact on these cognitive traits has been "almost nothing," challenging assumptions that modern civilization drives increasing intelligence.
  • This 'intelligence' isn't just about raw IQ; it's heavily correlated with broader executive functions, like a “propensity to defer gratification” and even the age at which women have their first child.
  • Modern environments may be actively working against the selection for these traits; Iceland, for example, saw a "huge" 0.1 standard deviation decrease in intelligence predictors in just one century.

The Bronze Age Brain Boom

Forget everything you thought you knew about intelligence and civilization. David Reich, a geneticist from Harvard Medical School, just dropped a bombshell: the human brain's biggest evolutionary upgrade in terms of cognitive capacity didn't happen in the age of ChatGPT. It happened thousands of years ago, when we were still figuring out bronze tools and early agriculture. Reich's new research, based on polygenic scores for traits like 'years of schooling,' shows selection for these cognitive traits “maxes out in the Bronze Age, between 5,000 and 2,000 years ago.”

This isn't just a slight bump. Dwarkesh Patel, the podcast host, called it “very surprising that the beginnings of civilization increased the selection on intelligence.” Our intuition tells us that complex societies, cities, and advanced technologies should constantly be pushing our brains forward. But the data says the opposite: “The impact in the last 2,000 years is almost nothing,” Reich says. The pressure to get smarter, or at least to carry the genetic markers associated with higher cognitive performance, largely faded after the Bronze Age.

Beyond IQ: The Real Signal

What exactly was natural selection favoring back then? It might not be 'intelligence' as we typically imagine it. Reich explains that the genetic predictors for 'years of schooling' – a proxy for cognitive performance – are “very strongly correlated to the age at which women have their first kid.” He points out a curious fact: “If you control for that, all of the signal of years of schooling goes away.” This suggests selection wasn't just for raw processing power. Instead, Reich speculates it might be for a broader, more fundamental trait. He waves his hands a bit, but offers a working theory: “There seems to be some kind of general trait that you could maybe think of as executive function or a propensity to defer gratification—I’m just waving my hands—that is under selection.”

Think about that. The ability to plan, resist impulses, and delay rewards might have been the true cognitive superpower our ancestors were selecting for. In a world with uncertain harvests and new social structures, the foresight to save, build, and cooperate for long-term gain would have conferred a massive advantage. It wasn't just about who could solve the puzzle fastest, but who could play the long game.

The Modern Drift: Are We De-Selecting?

If the Bronze Age was the peak, where are we now? Reich's research offers a stark warning: we might be going backward. He cites an estimated “0.1 standard deviation decrease in the genetic predictor of intelligence in Iceland just within one century.” That's a huge shift over a short period. In modern, comfortable societies, the intense selective pressures that favored executive function and deferred gratification seem to have vanished. We've built systems that reward short-term thinking, instant gratification, and the outsourcing of complex problem-solving.

For founders, this should be a wake-up call. If natural selection isn't doing the work, it's your job to actively select for the traits that build lasting value. Your current environment—from venture capital demands to social media dopamine hits—is likely pushing against the very executive functions and long-term vision that drove success in earlier, harder times.

What to Do With This

Stop assuming intelligence is a static, ever-improving resource you can rely on. Instead, explicitly test for a "propensity to defer gratification" in your hiring. During interviews, ask candidates about their biggest long-term projects, whether personal or professional, where they sacrificed immediate gain for a distant outcome. Look for evidence of persistent effort over years, not just quick wins. In your team, design systems that reward sustained focus on complex, slow-burn problems, even when immediate metrics don't jump. Your hiring funnel and company culture are now the primary selection mechanisms for the traits that truly build empires – not a naturally evolving world.