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

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 ...
STAGED INFECTION: Has The Ebola ‘Outbreak’ Narrative Fallen Apart?
2014 10 22
Over the past month, the ‘pandemic’ propaganda surrounding the deadly Ebola virus seemed to reach vitriolic levels – raising serious questions about the validity of this current viral outbreak… On Monday of this week, it was reported that 48 people were released and cleared after a 21-day quarantine due to their contact with the now deceased Ebola-stricken patient Thomas Eric ...
6,000-Year-Old Temple with Possible Sacrificial Altars Discovered
2014 10 21
A 6,000-year-old temple holding humanlike figurines and sacrificed animal remains has been discovered within a massive prehistoric settlement in Ukraine. Built before writing was invented, the temple is about 60 by 20 meters (197 by 66 feet) in size. It was a "two-story building made of wood and clay surrounded by a galleried courtyard," the upper floor divided into five ...
What happened to Journalist Serena Shim? Assassinated? Find out what happened to Serena, Press TV director calls on Turkey
2014 10 21
Press TV news director Hamid Reza Emadi says the “suspicious death,” of the news channel’s correspondent in Turkey is a tragedy for “anyone who wants to get the truth.” Emadi made the remarks in an interview with Press TV on Sunday following Serena Shim’s death across the border from Syria’s Kurdish city of Kobani, where the ISIL terrorists and Kurdish fighters ...
Ancient Roman Nanotechnology Inspires Next-Generation Holograms for Information Storage
2014 10 21
The Lycurgus Cup, as it is known due to its depiction of a scene involving King Lycurgus of Thrace, is a 1,600-year-old jade green Roman chalice that changes colour depending on the direction of the light upon it. It baffled scientists ever since the glass chalice was acquired by the British Museum in the 1950s, as they could not work ...
More News »