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Science Daily — Despite the explosive growth in size and complexity of the human brain, the pace of evolutionary change among the thousands of genes expressed in brain tissue has actually slowed since the split, millions of years ago, between human and chimpanzee, an international research team reports in the December 26, 2006, issue of the journal, PLOS Biology.

The rapid advance of the human brain, the authors maintain, has not been driven by evolution of protein sequences. The higher complexity of the biochemical network in the brain, they suspect, with multiple gene-gene interactions, places strong constraints on the ability of most brain-related genes to change.

“We found that genes expressed in the human brain have in fact slowed down in their evolution, contrary to some earlier reports,” says study author Chung-I Wu, professor of ecology and evolution at the University of Chicago. “The more complex the brain, it seems, the more difficult it becomes for brain genes to change. Calibrated against the genomic average, brain-expressed genes in humans appear to have evolved more slowly than in chimpanzee or old-world monkey.”

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A variation of a gene that controls the size of cholesterol molecules in the bloodstream is common among elderly Ashkenazim who remain mentally sharp.

If you live to 100, as roughly one in every 10,000 people do, you will likely want both your mind and body intact. Researchers have now discovered a gene that accomplishes just that, apparently protecting the brain as well as prolonging life.

The Longevity Genes Project, initiated by Nir Barzilai, director of the Institute for Aging Research at Albert Einstein College of Medicine, investigates people who live exceptionally long lives.

“There’s a strong family history of longevity in these people,” says Barzilai. “Research has shown the odds of having exceptional longevity are about 10 to 18 times more if you have a centenarian in your family. And these usually aren’t vegetarians or professional athletes. Some have smoked for 90 years.”

Barzilai and his colleagues examined 158 people of Ashkenazi, or Eastern European Jewish, descent who were 95 years of age or older. They chose Ashkenazi Jews since current generations stem from a relatively limited number of ancestors. This means they have a comparatively uniform genetic makeup, making it easier to identify important genetic differences.

The scientists gave these volunteers a common test of mental function, consisting of 30 questions. Correctly answering 25 of the questions meant a subject passed the test. Those centenarians who passed were two to three times more likely to have a common variant of a particular gene, called the CETP gene, than those who did not. When the researchers studied another 124 Ashkenazi Jews between 75 and 85 years of age, those subjects who passed the test of mental function were five times more likely to have this gene variant than their counterparts.

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