ADHD has benefited human ancestors
Attention deficit disorder is considered an aberration in modern society, where it is often necessary to concentrate on a single task. The authors of a new study found that for our distant ancestors, who were gatherers for most of their history, ADHD, on the contrary, provided an advantage: while relatives used a familiar resource, people suffering from the disorder were more likely to search for a new one.
Finding and obtaining hard-to-find food are considered important factors in the evolution of intelligence. They are related to the decision whether to stick with a known but potentially depleting food source or to look for something better. Models of optimal food search, based on the marginal value theorem, help us understand which decision a human or animal will make: an area with depleting resources is abandoned when consumption rates fall below the average for the environment. Hundreds of species tested - from bees to birds, monkeys and humans - behave as predicted by such models.
Attention Deficit Hyperactivity Disorder (ADHD) is a developmental disorder of the nervous system that affects 11 percent of children and 4.25 percent of adults and is mostly inherited. Its symptoms include distractibility as well as restlessness and excessive mobility.
The neurological basis of this disorder involves increased production of the neurotransmitter norepinephrine and increased activity in the neural circuits of the brain's passive-mode network, which are important for concentration. These features affect food-seeking behavior, prompting you to abandon what you have in search of something new.
The scientists decided to test whether people with ADHD traits would switch to searching earlier than those devoid of these phenotypic characteristics. To do this, the authors of the paper, published in the journal Proceedings of the Royal Society B, developed a virtual berry-picking game to assess the impact of ADHD symptoms on search behavior.
Participants in the game had eight minutes to pick as many berries as possible by pointing the cursor at a bush. Each time they picked from the same bush, the berry harvest was reduced, but they received a time delay when they changed bushes. Researchers initially hypothesized that more severe ADHD symptoms would be associated with shorter time on the same bush, as well as less optimal behavior and lower rewards in play.
A total of 457 people participated in the study. Overall, all players stayed on plots longer than the model predicted, and those with higher scores on the ADHD self-report scale changed bushes more quickly than the others. However, to the scientists' surprise, these participants also achieved higher reward scores. Their decisions to leave the bush were more closely aligned with those predicted by the model, although they still stayed on the bush longer than predicted.
Thus, in the implemented food search game, ADHD was associated with shorter dwell times and higher reward performance. These results echo previous field studies. For example, modern hunter-gatherers, such as the Aryaal tribe in northern Kenya, have genetic mutations associated with ADHD. All of this emphasizes that "everything in evolution is for a reason": ADHD did not emerge as a disorder, but rather as an advantage for that small percentage of its possessors in the population.