A study of Kenyan tribesmen has found that a genetic predisposition for attention deficit hyperactivity disorder may actually help nomads.
US researchers found that a gene associated with the disorder was linked to better health and body weight in a group of nomadic cattle herders, but could cause malnourishment in their cousins who have recently settled and begun to grow crops.
"Our findings suggest that some of the variety of personalities we see in people is evolutionarily helpful or detrimental, depending on the context," said lead author Dan Eisenberg, an anthropology graduate at Northwestern University.
"This insight might allow us to begin to view ADHD as not just a disease but something with adaptive components."
The dopamine receptor gene Eisenberg and his team studied is involved in impulsivity, reward anticipation and addiction and is believed to be associated with food craving as well as ADHD.
The effects of these genes have been studied in industrial countries but little research has been carried out in subsistence environments which more closely mirror the environments where much of human genetic evolution took place.
"It is possible that in a nomadic setting, a boy with this allele might be able to more effectively defend livestock against raiders or locate food and water sources, but that the same tendencies might not be as beneficial in settled pursuits such as focusing in school, farming or selling goods," Eisenberg said.
The study was published in the journal BMC Evolutionary Biology.