How did ADHD evolve and survive?

Michelle Dawson (without endorsing it) directs my attention to this paper:

The evolutionary status of attention deficit/hyperactivity disorder (ADHD) is central to assessments of whether modern society has created it, either physically or socially; and is potentially useful in understanding its neurobiological basis and treatment. The high prevalence of ADHD (5–10%) and its association with the seven-repeat allele of DRD4, which is positively selected in evolution, raise the possibility that ADHD increases the reproductive fitness of the individual, and/or the group. However, previous suggestions of evolutionary roles for ADHD have not accounted for its confinement to a substantial minority. Because one of the key features of ADHD is its diversity, and many benefits of population diversity are well recognized (as in immunity), we study the impact of groups’ behavioural diversity on their fitness. Diversity occurs along many dimensions, and for simplicity we choose unpredictability (or variability), excess of which is a well-established characteristic of ADHD. Simulations of the Changing Food group task show that unpredictable behaviour by a minority optimizes results for the group. Characteristics of such group exploration tasks are risk-taking, in which costs are borne mainly by the individual; and information-sharing, in which benefits accrue to the entire group. Hence, this work is closely linked to previous studies of evolved altruism.

We conclude that even individually impairing combinations of genes, such as ADHD, can carry specific benefits for society, which can be selected for at that level, rather than being merely genetic coincidences with effects confined to the individual. The social benefits conferred by diversity occur both inside and outside the ‘normal’ range, and these may be distinct. This view has the additional merit of offering explanations for the prevalence, sex and age distribution, severity distribution and heterogeneity of ADHD.

Overall the argument is weak because it relies too much on group selection.  An alternative tack is to admit that ADHD, and correlated traits, can have cognitive advantages and thus survival and mating advantages.  One simple story is that many people with ADHD can use their "jumpiness" to propel themselves to sample and learn extra new pieces of information.  The current distribution of identified cases from the ADHD population likely suffers from selection bias, namely that it identifies ADHD cases associated with greater life problems.

Addendum: Jerry Fodor has a recent paper challenging common applications of evolutionary psychology; Razib defends Darwin.


"The high prevalence of ADHD (5–10%) and its association with the seven-repeat allele of DRD4, which is positively selected"

Do we know what else that allele does? Do they consider that in the paper (my attention span for formal papers is not high, perhaps a little ironically)? That the allele is selected for doesn't necessarily have anything to do with ADHD, we have many, many imperfections that exist because they help do something else too.


Do you think there is a significant population of people who combine traits of autism/Aspergers and ADHD? Call them "jumpy" infovores or "Jeopardy champions"--people who must learn and order at least a little about a very wide range of subjects, always jumping from one to the next?

The fact that the argument lies on the idea of group selection is not in itself a weakness. Group selection has been long ago rehabilited in evolutionary biology has well as in sociobiology, as David Wilson and Edward Wilson clearly demonstrate here :

Group selection is a plausible mechanism but not a systematic one. Only case by case study can help to determine its strenght in evolutionary processes.

ADHD is particularly prevalent among high testosterone males with above average IQ's. I think it is a good idea to official register everyone in this group as having a "mental disability" and then making a law that people with a "mental disability" are nto allowed to own or possess a gun. This way will make the establishment much safer froma potential rebellion.

Or the impulse control problems of ADHD people just leads then to reproduce in larger numbers. Sort of like rabbits, risk takers die off at faster rate but they reproduce more rapidly to compensate.

Can you explain your reasoning that group selection is inherintly a weak argument? In evolutionary biology it plays a huge role from bacteria to the primates and has been major driver of traits considered "detrimental" to am individual.

Catana, I think your supposed to be drinking more sodium fluoride so that you will be as docile a concentration camp inmate.

I'm convinced that, to a large degree, attention deficit disorders are bred into children behaviorally. We cater to the natural tendency for children to crave immediate gratification and thereby program them to anticipate and demand more of the same.

We've got a real problem when kids can't stomach a 10 minute drive to the grocery store without popping in a DVD or jacking their brain into some other electronic entertainment option. But this is a problem of our own creation - we somehow feel that if we don't cater to and foster the perpetual and instantaneous digital stimulation of our children, we're somehow failing them.

Unplug your children, stop feeding them rocket fuel at every meal (and 2 snacks in-between) and you may find that their behavior is far more like that of a normal human being.

It seems that aspergers/ADD/ADHD people are less dependent on social norms and more dependent on self-constructed belief system...this is what is known as "anti-social"...therefore we as a society need to make every effort to fix these people...whether that means drugging them up or just railroading them into "special" schools we cannont let these anti-socials contaminate the healthy population with their sick minds.

the literature on dopamine receptor genes and behavior variation is huge. this paper is representative of a large class.

I'm not sure how important a role group selection plays in evolution, but I can offer two observations of ADHD behavior that may be helpful.

Any school administrator who moves quietly in and out of classrooms several times a day will tell you that the ADHD kids are almost always the first to notice you at the door or in the back of the room. I suspect that a hunter/gatherer group with some members who are constantly aware of changes in the local environment would have a survival advantage.

Rocket fuel food, high stimulation toys, television, lack of exercise, and parental indulgence all play a role in how genetic ADHD is manifested in a given child. That said, keep in mind that the modern world school environment(specifically requiring that children sit and concentrate for several hours every day)is brand new in evolutionary history and not always healthy or even a good preparation for adult life. How many rapid-fire-multi-tasking business execs have found their skill set to be better matched to business than it was to school?

When I was a kid, some friends of mine and I were playing with firecrackers. A friend of mine threw a firecracker into a large steel drum to see whether it would make an interesting noise. He said "Huh, it didn't go off." I said "mine did." See, I'd forgotten that I'd just lit a firecracker, and was still holding it. No serious injury, because they were pretty small firecrackers.

But you know what? The ability to forget an explosive device that you are holding, which you yourself just lit, in less than three seconds? That's actually pretty much a disability.

There are upsides and downsides. I think, though, it's important to recognize that even though there are certainly upsides, there are also certainly downsides. The net outcomes may be decent enough, and even beneficial for the group, but recognizing the limitations is important too. I think what's really broken is probably our notion of how we define a "disability". I think that, if I can't do something fairly basic that other people can, it's in society's best interests to try to accommodate me at least a little. That shouldn't be tied to whether or not I'm overall disadvantaged by the trait -- just to whether I have specific weak spots that can be mitigated by a bit of support.

I remember reading a book by Tom Hartmann in which he suggested that ADHD made a person a particularly good hunter. The ability to hyperfocus (stalk prey, make good weapons), coupled with easy distractibility (the hunter is also the hunted, so you need to stay on your toes) seems like a pretty good combination of traits to have when you're the hunting part of a hunter-gatherer tribe. In contrast, the gatherers need to be detail oriented, able to keep lots of tasks going at the same time, etc.

His other suggestion was that we've always had about the same percentage of people who were ADD, but our modern lifestyle has put the hunters at a disadvantage. If you find a career as a fireman, or a cop, or something else that allows you the kind of adrenaline and mental stimulation that ADHD people seek, you'll do fine. But put the same person behind a desk and ask him to shuffle papers all day, and he'll be a mess. As society demands more and more of the latter sorts of people, more and more are diagnosed as ADHD.

I don't know how well founded the theory is, and it's been at least a decade since I read it, so I can't remember the details. But it's certainly a theory that makes a lot of superficial sense.

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