ADHD may have improved the survival of foragers who knew when to stop

Evidence has emerged for the evolutionary benefits of attention deficit hyperactivity disorder (ADHD) in Paleolithic times, which may explain its presence today. The research conducted shows that ADHD is so beneficial that you may wonder why not everyone has it.

The presence of genetic conditions considered detrimental has been a conundrum at least since Darwin. In some cases, mutations that are too recent to have been eliminated by natural selection can be blamed, but the persistence of other traits only makes sense if we recognize that they are associated with factors that promote survival. These may be less obvious than the disadvantages, but can be just as real.

For example, conditions such as sickle cell anemia have long been recognized as a side effect of survival promoters, in which case partial protection against malaria for carriers. Now neurodiversity is viewed in the same way. It has been proposed that ADHD could help prevent collectors from wasting their time on fruitless searches, and now a team has found a way to test this idea.

Researchers from the University of Pennsylvania had volunteers play a foraging game and complete a task of finding as many berries online as they could find in a virtual bush within eight minutes. After finding the most obvious fruit, participants had the choice of staying in the same bush or migrating to another. The diminishing wealth of resources had to be weighed against the ‘travel time’ to a new bush.

Participants were not clinically tested, but were asked to rate themselves based on a proven ADHD study. A remarkable 45 percent met the level considered indicative of ADHD, well above the level in the population. Whether this was because the way participants were recruited resulted in more people with ADHD symptoms signing up, or because the test was conducted during the pandemic when ADHD symptoms increased even among people who were not normally affected, is unknown.

Whether they had ADHD symptoms or not, everyone in the study was more likely to move their patch if the travel time to the alternative was shorter. Any other outcome would indicate that there is something seriously wrong with the test, or you would wonder how humanity managed to survive in the first place.

Almost as predictably, people with ADHD symptoms were more likely to leave their forest than neurotypical people. Interestingly, participants stayed in the familiar area for longer on average, despite diminishing rewards, than mathematical models predict would be ideal. As a result, people with ADHD symptoms got 16 percent more berries, even though they lingered even longer than would have been perfect for the conditions.

This raises the possibility that the game may not accurately reflect the conditions in which humans evolve – for example, by not taking into account the energy required to travel between bushes.

Still, it makes it clear that under certain circumstances it is good not to be so tied to a task.

“Our findings suggest that ADHD traits may confer foraging benefits in some environments and point to the possibility that this condition reflects an adaptation that favors exploration over exploitation,” the study authors report.

If ADHD was a universal winner for our ancestors, we would expect almost everyone to have it. Furthermore, the authors note that hundreds of species’ approaches to such tasks have been tested, and all show similar patterns when it comes to leaving a familiar but declining area for new pastures. Something in our past must drive most people to stay in the same bush longer in this game than would be ideal.

Whether this is because most foraging tasks were not as depicted in the game, with higher penalties for moving too fast, or because perseverance was more useful in other tasks is unclear.

Either way, it’s likely that our ancestors benefited from the neurodiversity within the local population. Because some conditions favored those with the symptoms we now call ADHD, and some conditions favored those without symptoms, tribes fared best when they had mixed populations. Individual survival was as affected by the fitness of the tribe as the individual, so a diversity of mental approaches became a fixture in the population, with some not being labeled as disorders until much more recently.

A similar idea was recently proposed for developmental dyslexia, suggesting that having a few people who preferred exploring new environments over efficiently exploiting familiar ones might have been the key to survival in changing times.

The research has been published in Proceedings of the Royal Society B.

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