ADHD, Evolution and Survival

The basis of the theory of evolution is that random changes in genes will be passed down to future generations if they offer some advantage to survival of the species. In some cases, the advantages are obvious. Genetic mutations in birds that have changed the shape of their beaks have persisted because they were better able to capture insects to eat, or, like the hummingbird, to reach nectar deep inside flowers. The lengthening of the neck of the giraffe gave them access to food other species could not reach.  In human beings, sickle cell trait offers protection from early death from malaria and allows carriers to survive through reproductive age. When a child receives the trait gene from both parents, they suffer the painful and dreaded sickle cell disease. Nonetheless, the probabilities entailed in gene transmission guarantees a community added survival value from the sickle cell gene.

In some cases, the survival values of genes are not obvious. It has long been known that many psychiatric illnesses run in families and have genetic components. This prompts one to wonder what possible advantages could be gained from genes that manifest as psychiatric disorders. The heritability of Major Depression is thought to be about 50%, with the other 50% due to psychological and social factors.  Although Major Depression is a potentially dangerous and destructive condition, the fact that it is partly inherited suggests that it might offer some benefits.  Perhaps the experience of Major Depression can lead to the growth of compassion and understanding in those who suffer it. That, in turn, may produce individuals who are more kind and nurturing, and who can build stronger bonds in families and relationships.  Even schizophrenia, with genetic contribution ranging from 60 to 80%, may have some value to society that has kept the disorder in the human gene pool.  Ancient cultures often showed reverence towards those who heard voices and had unusual patterns of thinking. They were seen as communicating with gods and powerful beings that could offer help and guidance. Their ways of seeing the world may even have contributed to religious views that gave solace and stability to societies. Rather than being stigmatized and locked away, as they have tended to be in modern society, these people were often given lofty positions as shamans and oracles.

Attention Deficit Hyperactivity Disorder, or ADHD, can be a very difficult condition.  Its symptoms include being easily distracted, forgetful, impulsive, poorly organized, fidgety, and overly talkative.  Adults with untreated ADHD tend to have higher risks of dropping out of school, unemployment, divorce, substance abuse, and arrest. ADHD is thought to affect about 6% of the American population, and its heritability is about 80%, which is higher than for most other psychiatric illnesses. Considering all of the problems that ADHD can cause, it is hard to imagine how it might offer anything positive. But its persistence in the gene pool with a high inheritance rate suggests that it must offer some benefits to mankind.  

A recent study by David Barack, PhD and his colleagues at the University of Pennsylvania explored an important way by which ADHD may have contributed to the survival of human beings. It evaluated how those with ADHD strategize methods of foraging for food. They created a computer simulation of foraging for berries. Subjects picked digital berries from “berry patches” they chose on the computer screen. For incentive, they were given money for each berry they picked. As would be the case in real life, the longer they stayed in a particular berry patch, the scarcer the berries became. Subjects were given a choice to stay in a patch with diminishing returns or switch to another. The decision was complicated by the fact that while the patch they would arrive at would likely have more berries, time that might otherwise be devoted to picking berries would have to be spent traveling to the new patch. The simple choice to stay or move on to the next patch  produced two types of strategies, exploitation or exploration. That is, to stay as long as possible to exploit what berries might still remain in a patch, or to risk moving on to explore other patches where berries might be more plentiful.

It turned out that individuals that had been diagnosed with ADHD tended to choose the exploration versus the exploitation strategy. More importantly, by following the exploration strategy, they tended to find more berries than those who chose the exploitation strategy. Thus, they were more successful foragers. Many nomadic tribes that continue to forage for their food in real life also choose the exploration strategy.  One example is the Ariaal, a tribe of Kenya. These people who survive by foraging have a high presence of the long DRD4/7R allele, a variant of a gene for dopamine receptors commonly seen in ADHD. The same DRD4/7R allele is also seen in higher proportions among American Indian tribes who were once successful foragers, including the Pima, Muskogee, and Cheyenne.  Along with the “moving on” form of foraging strategy, this DRD4/7R allele common in ADHD is also associated with long and bold migrations across the globe. Malaysians, Samoans, and Micronesians whose ancestors migrated from Taiwan several thousand years ago show this ADHD-related long allele more often than the Taiwanese aboriginal people that were content to remain on the island. The same allele is also disproportionately high among Jews whose ancestors migrated a longer distance westward from the Middle east to Rome and Germany in comparison to those who migrated a shorter distance southward to Ethiopia and Yemen. Certain tribes of South America, whose ancestors migrated out of Asia, across the Bering land bridge, and through two continents, have among the world’s highest proportions of members carrying the DRD4/7R allele associated with exploring, risk-taking and ADHD. In some cases, this reaches 75%.

Advantages from ADHD in foraging for food may seem to be of little consequence for advanced human societies. However, while few modern humans forage for food to survive, people forage for other things.  We also forage our minds for ideas, thoughts, and new ways of doing things. Studies have shown that strategies for foraging for thoughts and ideas are quite similar to those used in foraging for food. The willingness to explore options rather than exploiting diminishing resources likely extends to ways of thinking, which may be the basis of what has long been suggested to be a tendency toward increased creativity in ADHD. Indeed, some of the most brilliant and creative thinkers in modern times, including Albert Einstein, Marie Curie, Thomas Edison, Alexander Graham Bell, Henry Ford, and Pablo Picasso have all been suspected of having shown the signs and symptoms of ADHD. Thus, while ADHD may cause great suffering, in some circumstances it may lend advantages to the modern mind.

The demonstration of positive aspects of ADHD does not mean the condition should go untreated. But emphasizing the potentially useful aspects of ADHD may aid in coping with ADHD, reduce stigmatization, and increase the quality of life of patients.  Of note, the medications generally used to treat ADHD, such as methylphenidate and amphetamine, are fasting acting and have short durations. Thus, It may be possible to take so-called “drug holidays” for several days to enjoy possible benefits from the risk-taking and creativity of ADHD, while being able to quickly restart medications for the daily activities that are facilitated by such treatment. The finding and use of means to exploit the positive aspects of ADHD is an approach that is largely unexplored, but it may yield benefits.