Is evolution keeping us dumb?

A new research paper argues that there are limits to our mental evolution and that humans are not likely to ever develop a "supermind."

Studies of human evolution show that as natural selection, nutrition, and medical technology have improved, so has the upward trajectory of the human body. But Thomas Hill and Ralph Hertwig write in Current Directions in Psychological Science that our bodies may have their own self-imposed evolutionary ceilings.

"A lot of people are interested in drugs that can enhance cognition in various ways," Hill and Hertwig write. "But it seems natural to ask, why aren't we smarter already?"

According to Hill and Hertwig, humans have grown in height over time but because of the limited ability of the heart to pump blood to the brain, it would not be feasible for people to suddenly become eight feet tall. Likewise, sudden growths in brain capacity are most likely limited by our own evolutionary caps:

A baby's brain size is thought to be limited by, among other things, the size of the mother's pelvis; bigger brains could mean more deaths in childbirth, and the pelvis can't change substantially without changing the way we stand and walk.

Hill and Hertwig also argue that supposed cognitive-enhancing drugs like Ritalin and amphetamines may temporarily improve focus, but usually only work on people with "lower baseline abilities," and those who don't suffer from conditions like Attention Deficit Disorder actually perform at lower levels under their influence.

"If you have a specific task that requires more memory or more speed or more accuracy or whatever, then you could potentially take an enhancer that increases your capacity for that task," the two write. "But it would be wrong to think that this is going to improve your abilities all across the board."

And then there are the psychological and emotional issues associated with higher intelligence. Hill and Hertwig point to conditions like post traumatic stress disorder, a condition brought on when someone literally cannot forget a past trauma. They also point to the case of the Ashkenazi Jews, who possess IQ's significantly higher than the general population of Europe but also disproportionately suffer from Tay-Sachs disease.

"Memory is a double-edged sword," Hills says. "If something bad happens, you want to be able to forget it, to move on."

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