Study says human brain still evolves

U. of C. researchers find growth genes keep rapidly mutating

September 09, 2005|By Ronald Kotulak, Tribune science reporter.

Could you use more brainpower?

Nature apparently thinks you can, according to two University of Chicago studies providing the first scientific evidence that the human brain is still evolving, a process that may ultimately increase people's capacity to grow smarter.

Two key brain-building genes, which underwent dramatic changes in the past that coincided with huge leaps in human intellectual development, are still undergoing rapid mutations, evolution's way of selecting for new beneficial traits, Bruce Lahn and his U. of C. colleagues reported in Friday's issue of the journal Science.

The researchers found that not everyone has these genes but that evolutionary pressures are causing them to increase in the population at an unprecedented rate. Lahn's group is also trying to determine just how smart these genes may have made humans.

One of the mutated genes, called microcephalin, began its swift spread among human ancestors about 37,000 years ago, a period marked by a creative explosion in music, art, religious expression and tool-making.

The other gene, ASPM (abnormal spindle-like microcephaly-associated), arose only about 5,800 years ago, right around the time of writing and the first civilization in Mesopotamia, which dates to 7000 B.C.

"People have this sense that as 21st century humans we've gotten as high as we're going to go," said Greg Wray, director of Duke University's center for evolutionary genomics. "But we're not played out as a species. We're still evolving and these studies are a pretty good example of that."

Just as major environmental changes in the past, such as dramatic shifts in the climate, food supply or geography, favored the selection of genetic traits that increased survival skills, the pressures on gene selection today come from an increasingly complex and technologically oriented society, said Lahn, a professor of human genetics and a Howard Hughes Medical Institute investigator.



Evolutionary changes occur when a member of a species experiences a mutation in a gene that gives him a new skill, like running faster, seeing farther or thinking better. The genetic mutation increases his likelihood of survival and having more children, thereby allowing the new mutation to spread quickly through the population.

That's what happened to the microcephalin mutation, which now occurs in 70 percent of all people, and the ASPM gene mutation, which so far has spread to 30 percent of all people.

Other experts called the U. of C. studies stunning but said that while the two genes appear to make people smarter by helping to engineer bigger brains, there are many more genes involved in brain building and human intelligence and cognition.

"It's very exciting but it's really just the beginning of a whole new phase of research," Wray said. "These aren't going to be the only genes and these aren't going to be the only changes. We don't even really know exactly what these changes mean, but it's a glimpse into the future of our understanding of how the human brain came to be and function the way it does."

Probing the genes of intelligence has been controversial in the past and is likely to be so now because of fears that the knowledge could be misused to grade people's intelligence based on their genes.

But intelligence is a complex issue that is greatly influenced not only by the genes people inherit, but also by their early learning experiences.

Researchers have learned over the last two decades that genes and the environment work together--genes provide for a range of possible outcomes and the environment determines which specific outcome is likely to occur.

Most of the brain, for instance, gets built after birth when learning experiences determine the way in which brain cells connect to each other. How a brain gets wired directly affects its computing power.

"There are genetic differences that make each of us unique," Wray said. "But there's no way for you to look at a single gene and say `OK, you've got this mutation, you're smarter than someone else.' Maybe at some point we will know that but not with these genes."

Ever since the human line diverged from other primates between 6 and 8 million years ago the human brain grew steadily bigger as a result of selective genetic mutations. Chimps, our closest primate relative, on the other hand, stayed pretty much the same.

Some 200,000 years ago, the anatomically modern human emerged with a brain three times the size of a chimp's. As humans got smarter, Lahn said, selection pressure for smartness became intensified.