Is there an evolutionary advantage to ADHD?

This week’s news story centres around Attention deficit hyperactivity disorder, also known as ADHD, which is a neurodevelopmental disorder which typically presents with inattention, impulsive behaviour, and hyperactivity. For those that have been diagnosed, or have been waiting a long time hypothetically, the treatments would imply that ADHD is something of a detriment in this day and age. But this study, published in the journal Proceedings of the Royal Society B: Biological Sciences, has a theory that not too long ago, such a genetic mutation may have been somewhat beneficial.

Will - I have to say for a genetic study, this has to be one of the most out there methodologies I've ever looked at. What happened, what was involved, and why were people foraging for berries?

Shivani - Yes, it's definitely different to sampling skeletons. So this time they had an interactive video game online and they had a couple hundred people essentially scavenge for berries on bushes and it was under time pressure. So they could either stay at the same bush looking for berries or they could move on to another bush, which used up time, but they may or may not find even more berries. So it was a trade off between time spent, a number of berries collected and then they took the scores of these couple of hundred people and also then screened all of them for symptoms of ADHD, which currently in the UK we diagnosed with the DSM-5 criteria. And it was found that people who displayed traits of ADHD actually scored higher and spent more time moving on to new pastures to look for berries essentially.

Will - So all these years when I've been told I'd get distracted too easily that I could just have been retorting with yes, but I'm going to find the next patch of good looking berries sooner than a potential rival.

Aylwyn - I mean, more generally, it's an example of the kind of thing that we see quite a lot in evolution where there is a particular trait behaviour. It doesn't have to be behaviour, it could also be some other more physiological trait. Something like risk of certain diseases that may actually have evolved in conditions where there was some benefit that came from that. Maybe there still is some benefit that came from that, but there's also a cost in other conditions or in other environments or at other times.

Will - It's an interesting one because I suppose in many ways, and I think the study and the later conversation around it hinted that whilst ADHD is is good for when you have rivals, it's less good for when you have to kind of attenuate berry collecting to seasons like our ancestors would've done. So again, there is still a trade off there that you'll be better against people of your own species, but you might not be able to keep time so well when you need to know the seasons well enough to collect berries naturally.

Aylwyn - Yeah, and that's going to be true of any adaptive trait to be honest. There's, it's always gonna be a relative thing. Are you doing better in this condition in this environment than people with the other version or with some other kind of behaviour there? And if so, then you'll have the advantage. But there might come a time where that's no longer the case or might come conditions where it's not the case and then you are at a disadvantage. One of the problems with trying to decide whether or not something has evolved like this is it's actually, people have found ever since Darwin, that it's actually quite easy to come up with plausible arguments for why something was beneficial. The problem is that because it's quite easy to come up with these stories, that they sometimes are given the term 'just so' stories because we're not sure if they're true or not. So how do you establish that actually something, this really was the cause that there really was an evolutionary advantage that that came from this?Rather than it just being some side effect or consequence of something else happening in evolution.

Will - Not to put you on the spot here, but is there any answer to that?

Aylwyn - There is some independent evidence and that comes from genetics from the genome. You can go and look if you have some idea about what genetic factors are associated with this trait. So in the case of ADHD, we know that there are some genes, versions of some genes that make you more likely to, to have ADHD and therefore it has, you know, there are some heritable components. Not that they're entirely causal, there are lots of other factors involved in environmental factors, but if you know that there are genetic factors, you can go and look at those gene variants and see when did they arise? Can you date the time when those variants appeared or when they rose in frequency. And we can do that now because we have all of these genomes from people all around the world and we've got ancient DNA, so we can actually go and look in many cases at genomes in the past and we can see did they have this particular gene risk allele? Was it present at one point in time or at low frequency and then high frequency later. And people have done that, I believe, with ADHD and I think they find that it's not so clear in fact this, these versions of these variants have been around for quite a long time. Neandethals, for example, have the genes that we associate with ADHD. So it's actually something that may have been with us for a very long time in our evolution. It's not so clear that it evolved recently in response to changes in human population sizes or subsistence strategists or something like this. So the story I think is still a little bit confused as to whether or not this explanation really holds.

Will - And Shivani, from the medical side of things because it's always been touted to me that ADHD is detrimental and it requires behavioural therapy or medication regardless of whether it's an evolutionary advantage or not. Does this kind of almost skew the way we look at it and perhaps there should be more social or medical shift in the ways that we look and treat this?

Shivani - Absolutely. And I think not just for ADHD, but things like autism, it's interesting that the term disorder or disease are being used to classify these things because I guess if you look at how societies changed before it was better to be stronger or faster when we had to hunt for our food. Things that benefited that were selected for. And now, society has moved to emphasis placed on things like intelligence or focus or academia. So how can you say traits that benefit certain jobs or how humans were tens of thousands of years ago are now a disorder. It's just sort of coming back to the fact that humans are different. Every human is different to the other human and everything lies on a spectrum and certain people are better at things than others. And in the case of autism, I mean, there've been studies showing that people with autism should really be really valued members of society. I mean they can be proficient musicians or painters or have really great focus and attention to detail and probably will outperform someone who doesn't have autism on a variety of tasks and jobs. And likewise for ADHD, it's definitely a condition that negatively affects a lot of children. And increasingly there are parents who are worried that their child isn't able to focus at school. And that's why I suppose medical professionals are quite quick to jump to things like medication or therapy because they might feel that in comparison they need that to kind of stay on average. So I think the terminology disorder is wrong and there shouldn't really be so much stigma in terms of having this diagnosis. And we should shift to how we can support these people better or how we can align them to career paths that they're better suited to because not everyone is good at the same thing. And that's what makes society function, I think.