Humans are slowly losing their cognitive capabilities as adverse genetic mutations fail to be weeded out by evolutionary pressures, according to a bold hypothesis put forward by Dr. Gerald Crabtree of Stanford University.

"I would wager that if an average citizen from Athens of 1000 BC were to appear suddenly among us, he or she would be among the brightest and most intellectually alive of our colleagues and companions, with a good memory, a broad range of ideas, and a clear-sighted view of important issues. Furthermore, I would guess that he or she would be among the most emotionally stable of our friends and colleagues," the leading geneticist began his article in the scientific journal Trends in Genetics, adding the same could be said of the "inhabitants of Africa, Asia, India, or the Americas."

Crabtree explained that human intelligence and emotions relied on thousands of genes, which acted together as links in a chain rather than individual components. A mutation to any of one of these genes can produce intellectual or emotional disability -- and research has found that most of these genes are particularly susceptible to mutations.

Under the harsh circumstances that ancient humans endured, even a slight reduction in cognitive abilities could doom an individual. Those with lower cognitive abilities were more likely to die before reproducing, leaving only those with more refined cognitive abilities to pass on their genes.

Based on human's current intellectual and emotional abilities, Crabtree speculates that our ancestors lived in a world "where every individual was exposed to nature’s raw selective mechanisms on a daily basis."

The peak of human intelligence occurred 50,000 to 500,000 years ago, says Crabtree, when selective pressures were at their greatest.

But as humans moved from small bands of hunter-gathers to dense agriculture-based societies, the "survival of the fittest" thankfully became less and less of an every-day reality. According to Crabtree, this transition had the side-effect of taming natural selection. The lack of evolutionary pressures prevented adverse genetic mutations that slightly reduced human's cognitive abilities from being eliminated.

Crabtree's hypothesis does not predict a future chock-full of dimwitted humans, however. Any noticeable decline in human cognition would likely take hundreds, if not thousands, of years. Human society will probably overcompensate for the problem long before then.

"One does not need to... have visions of the world population docilely watching reruns on televisions they can no longer build," he concluded. "Remarkably, it seems that although our genomes are fragile, our society is robust almost entirely by virtue of education, which allows strengths to be rapidly distributed to all members."

[Human brain via Shutterstock]