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Did the gene for ADHD help our nomadic ancestors?

June 17, 2008

An ADHD-associated version of the human gene DRD4 is linked to better health among nomadic tribesmen, but may cause malnourishment in their settled cousins, according to new research by a team directed by an anthropologist at the University of Wisconsin-Milwaukee (UWM).

A study by UWM assistant professor Ben Campbell and colleagues from Northwestern University, Boston University and UNLV shows that a particular version of the gene DRD4, appears to have completely different effects, depending on one's environment.

The DRD4 gene codes for a receptor for dopamine, one of the chemical messengers used in the brain. Previous research has linked the gene with Attention Deficit Hyperactivity Disorder-type behavior in young men - risk-taking, reward-seeking and impulsivity, says Campbell.

But people can have different versions of the gene. One variant, called the 7R allele, is associated with novelty-seeking in addition to ADHD.

The researchers conducted the study among the Ariaal population in northern Kenya - some of whom still live as nomads, while others have recently settled. The research team analyzed the body mass index (BMI) and height of the two groups, nomadic and non-nomadic Ariaal men, who had the variant gene.

They found that those with the 7R allele in the nomadic population were better nourished than their non-nomadic brethren who carried 7R allele.

The results underscore, says Campbell, the complexity of genotype on the expression of behavior. Different environments can determine whether behaviors associated with the gene, such as ADHD, are more or less effective.

"We may have difficulty understanding ADHD in part because we are considering the behaviors associated with it in only one environment - the present one," he says. "The thinking used to be one gene, one outcome. Now we know that one gene with different environments yields different outcomes."

Campbell says the results have implications for the relationship between a sedentary lifestyle and aging.

"This suggests that this particular allele may be beneficial in a traditional setting with high levels of habitual physical activity, but carries with it longer term costs in a more sedentary setting."

Although the effects of different versions of dopamine genes have already been studied in industrialized countries, very little research has been carried out in non-industrial settings, says Campbell. And yet, subsistence environments are more similar to those where much of human genetic evolution took place, he points out.

University of Wisconsin - Milwaukee