Why did ADHD evolve?
So we know that ADHD has been around for a long time and that rates of diagnosis are increasing. Some statistics are even suggesting we make up as much as 10% of the population. This begs the question: Why are rates of ADHD so high?
Firstly, this blog today is based on a YouTube video I put out. If you would prefer to watch instead of read, you can find the video here:
I am someone who has always been pretty neutral about my ADHD. When I got diagnosed I had a bit revelation of why certain things in my life were like they are, feeling validated for some things that I thought were personal failings but also realising how ADHD was responsible for some amazing parts of my life, such as the fact I play multiple instruments to a high standard (instead of just one to an amazing standard!).
Since I was diagnosed I went into a deep hyperfixation (that has thankfully subsided into a more manageable general interest) into learning as much as I could about ADHD and how my brain worked and one day I stumbled across something that made me pause. It was just one sentence, and it said: “There must be an evolutionary advantage for why ADHD exists”.
That kind of blew my mind a bit because it just made sense. ADHD is so prevalent, it makes sense that it evolved in our populations for a reason. The place I saw this message didn’t elaborate any further on what those evolutionary advantages might be or point towards any specific evidence so I knew this was something I’d have to research on my own. And so I have!
So today I’m going to take you through three papers that explore the relationship between ADHD and evolution to discuss where the current research is at on this topic.
The first paper I want to look at is called “How evolutionary thinking can help us to understand ADHD” and was published in 2018. The premise of this paper is that ADHD symptoms can be considered as “adaptive” to their specific environment. However the environment we find ourselves in today is vastly different from even 50 years ago, let alone the timescale needed for human evolution, thus we find ourselves today in a situation where ADHD symptoms are maladaptive to the environment they find themselves in.
They particularly focus on the example of children in school, and how we as a species didn’t evolve for our children to sit and self-regulate through school all day and that many of the difficulties that ADHD children present with at school are for precisely this reason.
The classroom situations we find ourselves in now are very different to how children grew up in the past
This paper is very interesting in that it goes through correlations between ADHD and other life factors, such as one that I’d never heard of before like apparently those born later in the academic year are more likely to receive an ADHD diagnosis than their older peers, but what I find really interesting is when it gets to talking about our genes.
There has been an association between ADHD and the long version of the gene DRD4, one that is associated with novelty seeking. This gene is found in approximately one seventh of the Kenyan tribe the Ariaal. Some of the tribe still follow a nomadic lifestyle, whereas others are now more settled. It was found that men with this novelty-seeking allele were well-nourished and healthy, whereas their counterparts in the more settled group were less well-nourished. The study goes on to conclude that the novelty-seeking allele found in ADHD is more useful for a less settled lifestyle.
In a way this intuitively makes sense. Our brains struggle with getting enough dopamine, therefore we seek out novelty to gain more dopamine, and therefore this novelty seeking behaviour is likely to be evolutionarily rewarded for a nomadic tribe.
Unfortunately, it’s not all that simple. While ADHD is associated with the DRD4 gene, the second paper we will look at, Empirical tests of natural selection-based evolutionary accounts of ADHD: a systematic review (Thagaard et al., 2016) notes that not everyone with ADHD has this allele and not everyone with this allele has ADHD. I do wonder to what extent this is due to issues with the diagnostic process but to be honest the second point around this in the paper convinces me more, and that’s that ADHD is likely more complex than just being able to be given by a single gene.
We’ll come back to this paper later, but I wanted to mention it in context now when talking about the potential overlap between DRD4 and ADHD.
Back to the first paper, it comes to the conclusion that if our advantage is in the area of novelty-seeking, sitting down and self-regulating is something that we’re naturally going to find tough, and I don’t know about you but I find that pretty tough myself. It then goes on to talk about how to reframe it. And you’re going to love this next point I think.
Because it points out that all of the discourse around managing ADHD children is all about changing the children to make their behaviour conform more, to make them be more neurotypical. This teaches us to mask, to suppress our inner selves, to feel bad about ourselves because we can’t just do the thing that our neurotypical peers have no trouble with. They point out that the conversation rarely addresses changing the environment to suit the child and work better with their individual brain, something I am very big on talking about on this channel.
They even point out that schools have been leaning even further towards more academic subjects in recent years and ones that include more movement and physical skills development like physical education, woodworking and home economics are increasingly being removed from the syllabus in a number of countries.
Now I’m someone who was fortunate enough to do well in academic subjects at school but my biggest passions in life have always been in two very physical domains: music and exercise (although I hated PE at school but that’s for other reasons I won’t get into here). I personally find it heart breaking that many children are losing out on these things that have been hugely useful and important to my ADHD brain and am so glad I got the opportunity to fall in love with these things at school (or after school when it came to exercise).
I wasn’t put in piano lessons as a kid, it was actually through music classes in the first year of secondary school that I fell in love with the piano and it wasn’t until I was 14 that I got lessons. Without music classes I never would have found what has become my special interest.
After that lament, I’d like to return to the paper “Empirical tests of natural selection-based evolutionary accounts of ADHD: a systematic review” which takes this subject a little bit further. Published in 2016, it looks at the recent theories around ADHD and evolutionary benefits and examines the evidence that exists for these theories.
The paper opens with the notion that the fact that ADHD is highly impairing, highly genetic but also highly heritable presents a challenge to the natural selection theory of evolution, and that if ADHD is THAT impairing then we would expect it to affect the reproductive prospects of the ADHD individuals and therefore be selected out.
I feel like this statement is very interesting in the context of my recent post around whether or not ADHD is a disability and the idea of the value neutral model of disability; that ADHD can be locally disabling, that is impairing under certain conditions, while being value neutral when it comes to wellbeing. I don’t really want to re-hash the topic in detail here so I will move forward with the highly impairing assumption of the paper but I’d recommend going back to watch this if you’d like to hear a more nuanced view around ADHD and impairment.
The paper posits four such theories as potential evolutionary advantages for ADHD and if you’d like to dive into the sources for them I’d recommend looking into the paper as it’s really well-referenced, but I’ll lay out the theories here:
The first is the hunter-farmer theory, that those of us with ADHD are hunters, while everyone else are farmers. The theory is that inattentiveness allows us to monitor and take in the environment we’re in and notice any changes, that hyperactivity allows us to be energetic and tireless, and that impulsivity allows us to be flexible and change strategies as we need to.
The response-readiness theory takes the position that ADHD traits may be suited to rapidly changing environments with external threats and scarce resources. In this case, inattention would be vigilance, impulsivity as response-readiness and hyperactivity as exploratory behaviour, all of which would be adaptive to this environment.
The wader theory suggests that as we evolved to become bipedal tool-makers we had to wade along the shoreline to find food. Through doing this we lost most of our body-hair to be more streamlined when moving through water, therefore our children were unable to cling to our body hair (something which in itself sounds incredibly painful but is present in all other primate species) and thus needed to attract more attention. ADHD children supposedly instigate more contact with their mothers and therefore would be more likely to get the attention needed to be fed. This one feels a little tenuous to me but let’s continue.
This immediately made me think of baby gorillas hanging onto their mothers.
Finally, the fighter theory suggests that ADHD aggression was needed in the potential war between Homo Sapiens and Neanderthals.
Some of those theories make a little more sense to me than others but it’s a bit interesting that this paper doesn’t refer to the nomadic lifestyle theory from the previous paper I mentioned, particularly because as I mentioned earlier it goes onto debunk it. This paper instead seems to immediately move away from these theories in the search of papers it can review to see whether the papers aptly support the suggestions they make.
They ended up looking at three papers, the first two referring to the DRD4 gene I referred to earlier so I won’t repeat that. The third one they looked at was a computational study that found that populations containing approximately 5% unpredictable individuals “had a better chance of survival in ancestral environments characterised by changing conditions”, and noted that 5% is close to the prevalence of ADHD.
The paper then goes on to discuss whether people with ADHD can be considered unpredictable, with arguments for both sides. But it’s actually what comes next that it suggests as a follow up that’s most interesting. Here’s a quote:
“It could be possible to test individuals displaying various degrees of ADHD-behavior under circumstances mimicking key features of an ancestral environment (rapidly changing, time critical and resource depleted) (11). If the environmental mismatch hypothesis suggested by Jensen et al. is correct, individuals with ADHDtraits should outperform individuals without such traits under these circumstances.”
Can you guess what the next paper I found is?
Ending this one on a cliffhanger, I’ll be back next week with what comes next.
References:
How evolutionary thinking can help us to understand ADHD (Swanepoel et al., 2018)
If this resonates with you and feel you would be interested in talking to an adhd and autism-friendly coach, feel free to get in touch. If you’re looking for more blog posts, you can find them here.
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