Traits common to attention deficit hyperactivity disorder (ADHD), such as distractibility or impulsivity, might have been an evolutionary advantage for our ancestors by improving their tactics when foraging for food, researchers have said.
ADHD is a neurodevelopmental disorder with symptoms including impulsiveness, disorganisation and difficulty focusing. While estimates of prevalence have varied, diagnoses have been rising in many countries.
Now, researchers say while some of these traits tend to be viewed negatively, they might have helped people seek out new patches for foraging.
Dr David Barack of the University of Pennsylvania, who was the first author of the research, said the study offered a potential explanation for why ADHD was more prevalent than expected from random genetic mutations alone and – more broadly – why traits such as distractibility or impulsivity were common.
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“If [these traits] were truly negative, then you would think that over evolutionary time, they would be selected against,” he said. “Our findings are an initial data point, suggestive of advantages in certain choice contexts.”
Writing in the journal Proceedings of the Royal Society B: Biological Sciences, Barack and colleagues reported how they analysed data from 457 adults who completed an online foraging game in which they had to collect as many berries as possible within eight minutes.
The number of berries obtained from each bush decreased with the number of times it was foraged.
During the task, participants could either continue to collect berries from the bushes in their original location or move to a new patch – although the latter cost them time.
The team also screened participants for ADHD-like symptoms – although they stress this did not constitute a diagnosis – finding 206 participants had positive results.
The researchers found that participants with higher scores on the ADHD scale spent shorter periods of time in each patch of bushes than those with lower scores. In other words, they were more likely to abandon their current patch and hunt for a new one. Crucially, the team found such participants also gained more points in the game than those with lower scores on the ADHD scale.
The researchers said their results chimed with other work that suggested populations with nomadic lifestyles that benefited from exploring tended to have genes associated with ADHD.
However, they added the study had limitations, including that ADHD-like symptoms were based on self-report.
Barack said it was necessary to carry out experiments involving people diagnosed with ADHD and real-world foraging tasks, not least as the latter would involve far more effort to move between patches than in an online game.
Michael J Reiss, a professor of science education at University College London, who was not involved in the work, said while ADHD appeared to be linked to serious negative consequences, he and his colleagues had argued it may help in situations where physical activity and rapid decision-making were highly valued.
“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 characterised as impulsive. In our evolutionary past such behaviour may sometimes have been highly advantageous,” he said.
“ADHD can be a serious problem but it’s a problem in large measure because of today’s environments.” - The Guardian