Writing in the journal Trends in Genetics, Stanford University author Gerald Crabtree argues that life-and-death challenges early humans faced, in which nature selected the most intelligent to survive, just aren’t there in urban environments.

“The development of our intellectual abilities and the optimization of thousands of intelligence genes probably occurred in relatively nonverbal, dispersed groups of peoples before our ancestors emerged from Africa,” writes Crabtree.

He says that with the development of agriculture and emergence of urbanization, natural selection no longer weeded out mutations that spawned intellectual inferiors.

But Crabtree says that advances in genetics may eventually allow that process to be reversed, and possibly lead to even more intelligent generations in the future.

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