ADHD Traits Might Have Helped Hunter-Gatherers Collect More Food While Foraging, Study Suggests

Attributes connected to attention-deficit/hyperactivity disorder (ADHD) may have helped early hunter-gatherers when foraging for food, researchers report in a paper published Wednesday in the journal Proceedings of the Royal Society B.

In the new study, participants played an online berry-picking game. The researchers found that people who self-reported symptoms of ADHD abandoned depleted patches of virtual fruit more quickly—and they picked more berries overall.

The findings suggest that in some environments, ADHD behaviors can serve as an adaptation, and the study might explain why traits such as distractibility and impulsivity are common.

“If [these traits] were truly negative, then you would think that over evolutionary time, they would be selected against,” lead author David Barack, a philosopher and neuroscientist at the University of Pennsylvania, tells the Guardian’s Nicola Davis. “Our findings are an initial data point, suggestive of advantages in certain choice contexts.”

“Determining exactly how behaviors associated with ADHD may have been adaptive within past environments is difficult, and these results are compelling in that they demonstrate measurable differences in the foraging strategies employed by individuals with and without ADHD,” Dan Eisenberg, who researches human evolutionary biology at the University of Washington and did not contribute to the findings, tells New Scientist’s Chen Ly.

ADHD is a common neurodevelopmental disorder typically diagnosed in childhood that often lasts into adulthood, per the Centers for Disease Control and Prevention. Symptoms can include trouble paying attention, impulsive behaviors, fidgeting a lot and taking unnecessary risks. Eleven percent of children and 4 percent of adults have ADHD, according to the study.

These traits can affect how people would forage for food, because they might more quickly abandon one potential food source for another. In some human populations today that explore for food in a nomadic lifestyle, genetic mutations tied to ADHD are present, the study authors write.

The researchers wondered whether ADHD is “a legacy of the hunter-gatherer world,” Arjun Ramakrishnan, a co-author of the study and neuroscientist at the Indian Institute of Technology Kanpur, tells New Scientist.

To test this theory, the scientists had 457 people play an online berry-picking game in which they were tasked with gathering as many virtual berries as possible in eight minutes. To pick berries, study participants hovered their cursor over a bush on their screen. The number of berries they could pick from each attempt decreased as they repeatedly foraged from the bush. After each attempt, they could choose to pick from the same bush or move on to another with more berries, but precious time would come off the clock as they moved to the next bush.

The researchers also gave participants a survey online, screening them for ADHD traits. Questions included, “How often do you have difficulty concentrating on what people are saying to you, even when they are speaking to you directly?” The participants responded on a scale from “never” to “very often.”

In the paper, the authors note that they did not clinically diagnose participants with ADHD. Almost half of the participants screened positive for ADHD, which is ten times the rate seen in the general adult population.

Regardless, the team found that people who screened positive for ADHD switched from one patch to another more quickly in the game and picked more berries than those who screened negative. Participants got a small monetary reward ($3 at most) for picking berries.

“It is great to see experimental evidence from David Barack and colleagues that participants who score highly for ADHD are more likely to switch their foraging activities in ways that can indeed be characterized as impulsive,” Michael Reiss, a science education researcher at University College London who was not involved in the study, tells the Guardian. “In our evolutionary past, such behavior may sometimes have been highly advantageous.”

Annie Swanepoel, a psychiatrist at North East London NHS Foundation Trust who did not contribute to the findings, notes to New Scientist that the online game contained plenty of berries to pick, differing from the lived experiences of early hunter-gatherers, many of whom would have dealt with resource scarcity.

Will Sullivan | | READ MORE

Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.