The gene that came to stay

A gene thought by some scientists to foster a bold, novelty-seeking personality, as well as attention-deficit hyperactivity disorder (ADHD), apparently spread substantially in human populations over roughly the past 40,000 years, according to a new study.

One form of the gene gained evolutionary favor near the end of the Stone Age because it enhanced survival and reproduction, proposes a team led by biologist Yuan-Chun Ding of the University of California, Irvine. The form is now the second-most-prevalent variant of the so-called DRD4 gene, which codes for a type of dopamine receptor (DRD4) found on brain cells.

Ding’s team theorizes that prehistoric people who trekked from Africa to distant locales may have relied on nervy, intrepid individuals to lead the journey. Many bearers of this variant of the DRD4 gene would have had the requisite personalities to head up migrating groups, Ding’s group asserts in the Jan. 8 Proceedings of the National Academy of Sciences.

To study variations in this gene, the researchers scrutinized the DNA sequence of the gene in 600 adults from Africa, Asia, Europe, the Americas, and the Pacific.

The most common DRD4 arrangement–found in about two-thirds of people–differs slightly from several less prevalent variations of the gene, the researchers say.

In contrast, the novelty- and ADHD-linked form of the gene diverges markedly from the most common pattern. It’s likely that this version of the DRD4 gene, which occurs in a sizable minority of people worldwide, resulted from one or more unusual mutations of the common form and then increased in frequency as the Stone Age wound down, around 40,000 years ago, Ding and his coworkers theorize.

Although this gene conferred advantages in prehistoric times, it appears to stoke childhood behaviors that now get diagnosed as ADHD, the researchers add.

Nonetheless, in an earlier study, they found that children with ADHD who possess this particular form of the DRD4 gene do much better on attention tests than ADHD kids with different versions of the gene do.

Other scenarios may explain the spread of this specific DRD4 gene, say Henry Harpending of the University of Utah in Salt Lake City and Gregory Cochran of the research firm Reconstruction Concepts in Albuquerque, N.M., in a comment published with the new study. For example, the prehistoric advent of societies in which women produced most of the food would have left men with lots of time to compete for mates. In these groups, a gene facilitating risky “show-off” behaviors in men would have proliferated, the anthropologists suggest.