Intelligence

Is your mind changing? Scientists think so

By CAROLYN ABRAHAM

Friday, September 9, 2005 Page A1

MEDICAL REPORTER
http://www.theglobeandmail.com/servlet/ArticleNews/TPStory/LAC/20050909/BRAIN09/TPHealth/?query=DNA

Humans may be the brightest species on Earth, but provocative new research has concluded our brain has not yet reached its final form.

Scientists at the University of Chicago have found that two human genes involved in brain size and development are still evolving -- and, they suspect, mutating to make people smarter.

The team is so sure of its hunch that it has patented the genes with plans to develop tests to identify those who carry these potentially brain-boosting traits -- which appear to be more prevalent in some populations than others.

"We're envisioning what societies will want," said human geneticist Bruce Lahn, predicting that prospective parents, for example, might find such information invaluable.

In two papers published today in the journal Science, Dr. Lahn and his colleagues report that the specific gene mutations they have found appear to have swept across certain areas of the globe so quickly that they are practically the norm. With prevalence rates higher than 70 per cent in Europe, for example, the researchers argue that chance alone cannot explain the changes, which first sprung up at the same time that modern humans developed culture and language.

"The rise is so rapid, I was literally flabbergasted," Dr. Lahn said. Natural selection appears to favour the new form of these genes, he believes, because they must offer some advantage.

"I would bet my money that it has something to do with cognition," he said. "It is a reasonable hypothesis -- we are getting smarter."

The discovery sounds like hopeful news for the human species, but it has prickly social implications: Researchers found the mutations are more prevalent among some ethnic groups than others.

Testing 1,184 DNA samples from around the world, the researchers found, for example, that the frequency in West and sub-Saharan Africa is less than 10 per cent.

"My concern is that this is going to become justification for prejudices against certain groups," Dr. Lahn said, even as he stressed that the work is in its early stages and that the full role these genes play in brain development is little understood.

However, the Chicago group is preparing data on the relationship between these mutations and IQ scores.

Geneticist Steve Scherer, a senior scientist at Toronto's Hospital for Sick Children, agreed on the need for a "very conservative and cautious" interpretation of the data. But, he said, the papers from the Chicago group offer convincing evidence that these genes have evolved rapidly in modern humans.

The two genes in question, microcephalin and ASPM, are known to be involved in brain development because when they fail to function, they produce tiny brains and mental retardation.

In earlier studies, Dr. Lahn, a noted expert in genetics and evolution, also identified them as two of 17 genes that mutated millions of years ago and helped to triple the human brain in size, boost its sophistication and separate us from our closest relative, the chimpanzee.

All mutations begin as random events during conception. But they become more prevalent in a population if they offer a survival advantage, and if the people who carry them have more children than others.

As a result, Dr. Lahn and his team decided to study whether these genes are still evolving. They began by decoding the chemical sequence of the two genes in an ethnically diverse sample of 90 people. It was then that they first found startling evidence of the prevalence of these mutations in the genes. They verified their findings by sequencing DNA samples that had been previously collected, including an international sampling of indigenous people.

They found that a particular series of mutations in the microcephalin gene appears to have been passed on and is now, surprisingly, carried by large numbers of people from different ethnic backgrounds. They estimate this series first emerged about 37,000 years ago, around the time modern humans settled Europe and began producing art.

The changes they found in the ASPM gene are far more recent, springing up about 5,800 years ago, coinciding with the rise of cities and the first record of written language.

The studies do not answer where the mutations first arose, which may explain why these new genetic traits are not seen equally around the globe.

For one, the mutations may have arisen in Africa, but were then carried out by the early humans who left the continent to populate the rest of the planet. Alternately, Dr. Lahn said, they may have arisen in Europe or the Middle East.

(The study did not test widely in North America, which the researchers assumed to be largely populated by a wide variety of ethnic lineages.)

Dr. Lahn feels it's unlikely the mutations will lead to ever-larger human brains, since giving birth to babies with larger heads could itself threaten the species. But he does suspect the human brain's structure could be dramatically different a few thousand years from now.

"A lot of people, including biologists, think we are at the pinnacle of evolution . . . that the human form may be at the best form ever. They think that in the last 200,000 years [since the modern human emerged] there has just been a cultural evolution, and we're saying no, there is also genetic evolution."

September 10, 2005 at 06:30 PM in World affairs | Permalink | Top of page | Blog Home