Are People Getting Dumber? One Geneticist Thinks So
2012 11 27

By Rebecca Boyle | PopSci.com

A Stanford geneticist says humans have so many genetic mutations that we’re less intelligent than our ancestors, and it’s getting worse. Eugenicists 100 years ago had similar hypotheses.



There’s this great recurring “Saturday Night Live” skit from several years back where Phil Hartman plays an unfrozen caveman who goes to law school. He pontificates on the American judicial system while marveling at modern technology like “the tiny people in the magic box” (a TV). It fits a common stereotype: Human ancestors were, well, cavemen, and not as smart as we are today. A provocative new hypothesis from a Stanford geneticist tries to turn this stereotype upside down.

Human intelligence may have actually peaked before our ancient predecessors ever left Africa, Gerald Crabtree writes in two new journal articles. Genetic mutations during the past several millennia are causing a decline in overall human intellectual and emotional fitness, he says. Evolutionary pressure no longer favors intellect, so the problem is getting exponentially worse. He is careful to say that this is taking quite a long time, so it’s not like your grandparents are paragons of brilliance while your children will be cavemen rivaling Hartman’s SNL character. But he does posit that an ancient Athenian, plucked from 1000 BC, would be “among the brightest and most intellectually alive of our colleagues and companions.”

His central thesis is that each generation produces deleterious mutations, so down the line of human history, our intelligence is ever more impaired compared to that of our predecessors.

Not surprisingly, the hypothesis, published in the prominent journal Trends in Genetics, has several geneticists scratching their heads.

“It takes thousands and thousands of genes to build a human brain, and mutations in any one of those can impair that process, that’s absolutely true. And it’s also true that with each new generation, new mutations arise ... but Crabtree ignores the other side of the equation, which is selection,” said Kevin Mitchell, associate professor at the Smurfit Institute of Genetics at Trinity College Dublin, who operates the blog Wiring the Brain. “Natural selection is incredibly powerful, and it definitely has the ability to weed out new mutations that significantly impair intellectual ability. There are various aspects in these papers that I think are really just thinking about things in a wrong way.”

Crabtree said he wanted to examine the cumulative effect of generation-to-generation mutation on intelligence, which is thought to be controlled by many genes. Using indices that measure X-chromosome-related mental retardation, he comes up with between 2,000 and 5,000 genes related to human intellectual ability. Using another index measuring average mutations that arise in each generation of children, he calculates that within 3,000 years, “we have all sustained two or more mutations harmful to our intellectual or emotional stability.”

“There is a general feeling that evolution constantly improves us, but it only does that if there is selection applied,” Crabtree said in an interview. “In this case, it is questionable about how much selection is occurring now compared to the process of optimizing those genes, which occurred in the jungles of Africa 500,000 years ago.”

There’s already evidence for this in other areas, he argues: Take our sense of smell. Humans have far fewer olfactory receptors than other animals, he said--we’re guided by our intellect now, not by smell. We can think about where a piece of food came from, how it was processed, which plant it’s from, who has been around it, and so on. A dog, on the other hand, simply sniffs something and either eats it or doesn’t.

“Once you place pressure on intellectual abilities, and take it off of olfactory abilities, the olfactory genes deteriorate,” Crabtree said.

Similarly, he believes evolution now selects for other traits--namely, the most healthy and the most immune, not the most intelligent. Human movement into communities and cities increased the spread of infectious diseases, and those with the strongest physical constitutions survived to pass on their genes, he argues. He said he wanted to publish this hypotheses because geneticists can test for this, in an expensive process that requires saving some genetic information that typically gets discarded.


[...]


Read the full article at: popsci.com













Related Articles


Latest News from our Front Page

Norway Joins the Race to Develop Killer Robots
2014 10 24
Norway is a large exporter of weapons, which makes the resolution of the debate about creating killer robots an important issue for everyone.  One could debate the overall merits or failings of robotic systems, but an area that clearly has become a point for concern on all sides is the emergence of "killer robots." According to robotics pioneer, David Hanson, ...
Gene That Once Aided Survival in the Arctic Found to Have Negative Impact on Health Today
2014 10 23
In individuals living in the Arctic, researchers have discovered a gene variant that arose thousands of years ago and most likely provided an evolutionary advantage for processing high-fat diets or for surviving in a cold environment; however, the variant also seems to increase the risk of hypoglycemia, or low blood sugar, and infant mortality in today’s northern populations. {snip} “Our work ...
The Ebola hoax: questions, answers, and the false belief in the “One It”
2014 10 23
“The Reality Manufacturing Company doesn’t just sell ‘fake paintings’ that are easy to spot. No. They also sell images that are geared to mesh with people’s deeply held instincts and thereby produce rigid false beliefs. People are sure that if they gave up such beliefs, their world would fall apart and blow away in the wind.” ...
New Controversial Theory Suggests "Hobbits" Were Not Human - Who Were These Mysterious Beings?
2014 10 23
The origin of the Hobbit species remains a challenging subject to scientists. The Hobbit’s discovery confirmed the view that the Earth was once populated by many species of human, but new research the Hobbit’s were not human at all! So, who were these mysterious beings? Where did they come from? The idea that our species, Homo sapiens, was the only species of human on ...
Right into enemy hands? ISIS shows off new weapons allegedly airdropped by US (VIDEO)
2014 10 23
Islamic State has published a new video in which a jihadist shows off brand-new American hardware, which was purportedly intended for the Kurds they are fighting in the Syrian border town of Kobani. The undated video, posted by the unofficial IS mouthpiece “a3maq news”, sees a jihadist showing several boxes of munitions with English-language markings, with a parachute spread out on ...
More News »