Attention deficit hyperactivity disorder is a relatively common neurodevelopmental disorder, affecting between 5 and 10% of children. Its symptoms are a short attention span, excessive liveliness and impulsiveness, impatience. Characteristics of behavior that can represent an important limit in the school environment and, once adults, in the world of work. But in the past, perhaps, they had a completely different effect, proving useful for completing the daily search for food as our ancestors survived as hunter/gatherers.
The hypothesis
The intuition comes from research from the University of Pennsylvania, recently published in the journal Proceedings of the Royal Society B: Biological Sciences, which attempted to analyze the reasons why an evolutionary trait that today often proves disadvantageous is still so widespread in the world population. Statistics in hand, the researchers explain, the incidence of attention deficit hyperactivity disorder (also known by the English acronym ADHD) seems higher than what would be expected if it were linked to genetic variants that appear following completely random mutations . And therefore, it seems in some way to be the result of positive selection in the course of evolution.
“If these traits were purely negative, we would expect that in evolutionary times natural selection would have eliminated them,” explains David Barack, one of the authors of the research. “Our findings therefore represent a starting point, and suggest that they may provide some kind of advantage in some contexts.”
Which? The key is to imagine what lifestyle our ancestors had in the distant past, when natural selection was shaping the hominids who would become modern sapiens. In fact, they were nomadic groups of hunter gatherers, who entrusted their survival, largely, to the collection of berries, tubers and vegetables available in the environment to which their migrations took them. And in such a context – the researchers reasoned – the restlessness that makes it difficult to sit in class and concentrate on a lesson today could instead represent an advantage: a natural propensity to explore the environment which improved the chances of gathering the most number of resources possible.
The experiment
To verify their reasoning, the researchers decided to carry out an experiment, based on a mathematical model widely used in similar research, which tries to account for the fact that the more resources are taken from a site, the more they decrease and become difficult to find. ,
and it can therefore become more advantageous to look for a new site for the collection. In the simulation, this was represented by virtual bushes from which berries had to be picked. The more time you spent on a single bush, the fewer berries you could get, but at the same time changing bushes took time. 457 people were invited to participate in the simulation, and collect as many berries as possible in the space of 8 minutes.
Participants were tested to see whether they possessed character traits consistent with a diagnosis of ADHD, and the results of the character test were then compared to those obtained while picking berries. 206 participants showed that they had traits compatible with attention deficit hyperactivity disorder, and as ADHD traits increased in a participant, the time spent picking berries from each single bush decreased, and at the same time, the number of berries obtained at the end of the 8 minute experiment.
Clearly, the results are not sufficient, alone, to demonstrate the evolutionary value of ADHD. But they are in line with other similar research carried out in recent years, and therefore strengthen the hypothesis – already raised in the past by other research groups – that attention deficit hyperactivity disorder is a behavior that is harmful mainly due to the environment we live in nowadays, with its rigid rules, and the need to concentrate on repetitive tasks for long periods of time. And that in the past, in the completely different environment in which our ancient ancestors lived, things were completely different, so much so that it was positive and beneficial. It is no coincidence, the researchers point out, that some populations who still live the nomadic life of our ancestors, such as the Ariial of Kenya, are carriers of genes known to represent a risk factor for ADHD.