Evidence has emerged for the evolutionary benefits of attention deficit hyperactivity disorder (ADHD) in paleolithic times, potentially explaining its presence today. Indeed, in the study done, ADHD proved so advantageous it’s fair to ask why not everyone has it.

The presence of genetic conditions considered to be disadvantageous has posed a puzzle at least since Darwin. In some cases, mutations too recent to have been eliminated by natural selection can be blamed, but the survival of other traits only makes sense if we acknowledge they come with survival-enhancing factors. These may be less obvious than the drawbacks, but can be just as real.

Conditions like sickle cell anemia, for example, have long been recognized as a side-effect of survival enhancers, in that case, partial protection against malaria for carriers. Now, neurodiversity is starting to be considered in the same way. It's been proposed that ADHD may help stop foragers from wasting their time on fruitless searches, and now a team have found a way to test the idea.

University of Pennsylvania researchers had volunteers play a foraging game and perform a task seeking as many online berries as they could find within eight minutes on a virtual bush. After finding the most obvious fruit, participants had the choice of staying on the same bush or migrating to another one. The declining resource richness had to be weighed against the “travel” time to a new bush.

Participants were not clinically tested, but were asked to self-assess on a well-established ADHD survey. A remarkable 45 percent met the level considered indicative of ADHD, far above the level in the population. Whether this was because the way participants were recruited caused more people with ADHD symtpoms to sign up, or because the test was done during the pandemic when ADHD symptoms rose even among people not normally affected, is unknown.

Whether they had ADHD symptoms or not, everyone in the trial was more likely to move patches when the travel time to the alternative was shorter. Any other outcome would indicate something badly wrong with the test or make one wonder how humanity survived at all.

Almost as predictably, people with ADHD symptoms were more likely to choose to abandon their bush than neurotypical people. Interestingly, participants on average stayed longer in the familiar patch, despite declining rewards, than mathematical models predict would be ideal. As a result, people with ADHD symptoms got 16 percent more berries, although even they stuck around longer than would have been perfect for the conditions.

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

Nevertheless, it makes clear that under certain circumstances it’s a good thing to not be quite so stuck on a task. 

“Our findings suggest that ADHD attributes may confer foraging advantages in some environments and invite the possibility that this condition may reflect an adaptation favoring exploration over exploitation,” the study’s authors report.

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

Whether this is because most foraging tasks were not like the one the game portrays, with greater penalties for moving too soon, or because perseverance was more useful at other tasks, is unclear.

Either way, it is likely our ancestors benefited from the neurodiversity within local populations. With some conditions favoring those with the symptoms we now call ADHD, and some favoring those without, tribes did best when they had a mixed population. Individual survival was as affected by the fitness of the tribe as the individual, so a diversity of mental approaches became fixed in the population, with some only becoming labeled a disorder much more recently.

A similar idea was recently proposed for developmental dyslexia, suggesting having a few people who preferred to explore new environments over efficient exploitation of familiar ones may have been key to survival in changing times.

The study is published in Proceedings of the Royal Society B.