Just look at all the amazing innovations modern technology has given us: at-home HIV tests, motion-activated screwdrivers and self-inflating tires. It’s easy to look down on our prehistoric ancestors for their primitive, electric screwdriver-less way of life. But one scientist says we shouldn’t be so quick to judge.

In a two-part paper published in the journal Trends in Genetics, Stanford University researcher Gerald Crabtree suggests that evolution is, in fact, making us dumber - and that human intelligence may have actually peaked before our hunter-gatherer predecessors left Africa.

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The reason? Life on the veldt was tough, and prehistoric humans’ genes were constantly subjected to selective pressure in an environment where the species’ survival depended on it. For humans, that meant getting smarter. ”The development of our intellectual abilities and the optimization of thousands of intelligence genes probably occurred in relatively non-verbal, dispersed groups of peoples before our ancestors emerged from Africa,” Crabtree said in a news release.

The urbanization that followed the development of agriculture simplified survival by removing some of its challenges, which likely weakened natural selection’s ability to eliminate mutations associated with deficiencies in intelligence. Crabtree estimates that over the last 3,000 years (about 120 generations), humans have sustained at least two mutations that have eroded our intellectual and emotional intelligence.

“A hunter-gatherer who did not correctly conceive a solution to providing food or shelter probably died, along with his or her progeny, whereas a modern Wall Street executive that made a similar conceptual mistake would receive a substantial bonus and be a more attractive mate,” Crabtree wrote in the paper. He also noted that the average Athenian from 1000 B.C. would rank among the smartest and most emotionally stable in today’s society.

Not everybody agrees with Crabtree’s reasoning, however. Steve Jones, a geneticist at University College London, believes there is insufficient data to support his theory. ”Never mind the hypothesis, give me the data, and there aren’t any,” Jones told The Independent. “I could just as well argue that mutations have reduced our aggression, our depression and our penis length, but no journal would publish that. Why do they publish this?”

Crabtree does argue that no matter how deteriorated our intellectual abilities may have become over the millennia, advancements in technology will someday render these changes insignificant.

“I think we will know each of the millions of human mutations that can compromise our intellectual function and how each of these mutations interact with each other and other processes as well as environmental influences,” Crabtree said in the release. “At that time, we may be able to magically correct any mutation that has occurred in all cells of any organism at any developmental stage. Thus, the brutish process of natural selection will be unnecessary.”

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