Humans may be gradually losing intelligence, according to a new study.
The study, published today (Nov. 12) in the journal Trends in Genetics,
argues that humans lost the evolutionary pressure to be smart once we started living
in dense agricultural settlements several thousand years ago.
"The development of our intellectual abilities and the optimization of thousands
of intelligence genes probably occurred in relatively non-verbal,
dispersed groups of peoples [living] before our ancestors emerged from Africa,"
said study author Gerald
Crabtree, a researcher at Stanford University, in a statement.
Since then it's all been downhill, Crabtree contends.
The theory isn't without critics, with one scientist contacted by LiveScience suggesting that rather
than losing our smarts, humans have just diversified them with various types of
intelligence today.
Life or death situations
Early humans lived or died by their spatial abilities, such as quickly making a shelter or spearing
a saber-toothed tiger. Nowadays, though almost everyone has the spatial ability
to do ostensibly simple tasks like washing dishes or mowing the lawn, such tasks
actually require a lot of brainpower, the researchers note.
And we can thank our ancestors and the highly tuned mechanism of natural
selection for such abilities. Meanwhile, the ability to play chess or compose
poetry likely evolved as collateral effects.
But after the spread of agriculture, when our ancestors began to live in
dense farming communities, the intense need to keep those genes in peak condition gradually
waned.
And its unlikely that the evolutionary advantage of intelligence is greater
than it was during our hunter-gatherer past, the paper argues.
"A hunter-gatherer who did not correctly conceive a solution to providing
food or shelter probably died, along with his/her progeny, whereas a modern Wall
Street executive that made a similar conceptual mistake would receive a
substantial bonus and be a more attractive mate. Clearly, extreme selection is a
thing of the past," the researchers write in the journal article.
Intelligence genes
Anywhere between 2,000 and 5,000 genes determine human intelligence, and these genes are particularly
susceptible to harmful changes, or mutations, the researchers write. Based on
knowledge of the rate of mutations, the team concludes that the average person
harbors two intelligence-stunting genetic changes that evolved over the last
3,000 years.
The hypothesis is counterintuitive at first. After all, across the world the
average IQ has increased dramatically over the last 100 years,
a phenomenon known as the Flynn Effect. But most of that jump probably resulted
from better prenatal care, better nutrition and reduced exposure to
brain-stunting chemicals such as lead, Crabtree argues.
But just because humans have more mutations in their intelligence genes
doesn't mean we are becoming less brainy as a species, said psychologist Thomas
Hills of the University of Warwick, who was not involved in the study. Instead,
removing the pressure for everyone to be a superb hunter or gatherer may have
allowed us to evolve a more diverse population with different types of smarts,
he said.
"You don't get Stephen Hawking 200,000 years ago. He just doesn't exist,"
Hills told LiveScience. "But now we have people of his intellectual capacity
doing things and making insights that we would never have achieved in our
environment of evolutionary adaptation."
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