June 18, 2008
ADHD as a Beneficial Adaptive Trait?
Slate.com's WIlliam Saletan has a brief article discussing ADHD and its evolutionary origins. He writes that an understand of its potential usefulness in the past may help our society to adopt to ADHD rather than forcing individuals with ADHD to adopt to our societal standards. He says,
. . . . A new study suggests that this ADHD-friendly world may actually be part of our past.
The study, led by Dan Eisenberg of Northwestern University and published in BMC Evolutionary Biology, examined a Kenyan tribe called the Ariaal. Part of the tribe has recently settled into an agricultural community. Another part remains nomadic. The tribesmen were tested for DRD4 7R, a genetic variant that, Eisenberg notes, "has been linked to greater food and drug cravings, novelty-seeking, and ADHD symptoms." He and his colleagues report:
DRD4 7R+ genotypes were associated with indices of better nutritional status among nomads, particularly higher fat free mass, but worse indices in the settled individuals. This suggests that the 7R allele confers additional adaptive benefits in the nomadic compared to sedentary context. . . . .
But how would the gene help nomads? The authors speculate:
Increased impulsivity, ADHD-like traits, novelty-seeking like traits, aggression, violence and/or activity levels may help nomads obtain food resources, or exhibit a degree of behavioral unpredictability that is protective against interpersonal violence or robberies. …
I don't know whether the speculated reasons for the gene's benefits will pan out. But the benefits do seem real. And that finding suggests two things. First, we should be careful about designating diseases and disease genes. Traits that are harmful in one setting can be helpful in another. Advantages or "defects" that we think of as natural may actually be products of our cultural decisions. As Eisenberg puts it, we might "begin to view ADHD as not just a disease but something with adaptive components."
Second, our society may be the wrong place to assess a gene's evolutionary harm or benefit. As the authors note, "[N]on-industrialized or subsistence environments … may be more similar to the environments where much of human genetic evolution took place." . . . .
The lesson of the Ariaal study is simply that society can adapt to genes instead of the other way around. Maybe we don't have to screen and chuck embryos for every "disease" gene, or drug the kids once they're born. Maybe we can put ADHD kids in educational settings more like the dynamic environment of our nomad forebears. And maybe we can raise kids with fat-storage genes in settings less full of food. . . .
June 18, 2008 | Permalink
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