ADHD May Have Given Ancient Man A Survival Edge, Researchers Believe

Having attention-deficit/hyperactivity disorder (ADHD) is not usually thought of as providing an advantage in our society. But suppose some of the characteristics of ADHD were found in human ancestors. Could hyperactivity or shifting attention help a hunter survive in a world of mastodons and saber-tooth tigers?

This scenario is more than sheer fantasy, thanks to new findings from Robert Moyzis, Ph.D., a professor of biological chemistry at the University of California at Irvine, and his colleagues. The findings are reported in the January 8 online edition of the Proceedings of the National Academy of Sciences.

In the past several years, evidence has been mounting that a deficiency in the neurotransmitter dopamine may underlie ADHD (Psychiatric News, March 16, 2001). There has also been reason to believe that a particular variant of a gene called the DRD4 gene, which makes brain receptors for dopamine, may play a causal role in ADHD. For instance, about half of all youngsters with ADHD have this particular gene variant. Moyzis and his coworkers wanted to find out when this particular gene version might have arrived in the human gene pool compared with other variants of the same gene.

They analyzed genetic material from 600 individuals throughout the world for the presence of the DRD4 gene. They found 56 different variations of the gene, including the one implicated in ADHD. They then determined, via gene-recombination techniques, that the gene version implicated in ADHD is probably much younger from an evolutionary viewpoint than the other variants are. That is, they hypothesized that it probably arose as a spontaneous mutation as recently as 10,000 to 40,000 years ago.

When this version popped up, they suspected, it might have provided those humans possessing it with some evolutionary advantage over other humans who did not have it—say, being able to spring quickly to spear a mastodon. After all, around the time that the gene variant putatively made its debut, mastodons were roaming North America.

The study by Moyzis and his team was financed by grants from the U.S. Department of Energy and the National Institute of Mental Health.

An abstract of the study, “Evidence of Positive Selection Acting at the Human Dopamine Receptor D4 Gene Locus,” can be read online at www.pnas.org/cgi/content/short/99/1/309. ▪

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