This paper focuses on the past and current effects of the impulsivity trait associated with ADHD, specifically the hyperactive/impulse subtype of ADHD, also referred to as ADHD-HI. One of the main questions in the class discussion was what is the difference between ADHD and ADHD-HI…according to various medical websites, I discovered that ADHD, or attention deficit hyperactivity disorder, has three basic forms: primarily inattentive, primarily hyperactive-impulsive, and a combination of the inattentive and hyperactive-impulsive. The combination ADHD is the most common, the primarily inattentive kind is often seen, especially in girls and adults, but is less common than the combination type, and the hyperactive-impulsive type, as discussed in this paper, is rare.
The paper looks at the possible influences of the persistence of ADHD in the population. Since ADHD is associated with an allele that has been shown to be positively selected for since the appearance of the anatomically modern human, the seven-repeat allele of dopamine receptor type D4 (DRD4-7R), perhaps ADHD is also selected for. The authors suggest that ADHD’s most characteristic feature is behavioral variability, which manifests itself as impulsivity, the willingness to take risks, and novelty-seeking. Since novelty-seeking has also been associated with DRD4-7R, the authors propose that perhaps this trait has been selected for and is beneficial to certain types of society, including female-dominated farming and migratory societies. This might explain why the DRD4-7R allele is prevalent in South America. Those who migrated to South America as an empty ecological niche would be more likely to explore if prone to novelty-seeking.
The authors seem to be examining the possibility of whether ADHD-HI have been selected for as a benefit to individual fitness. Besides being adaptive in the sense of behavioral variability, the authors suggest several other ways it might be adaptive to the individual: having the ability to gain maternal attention, to be more creative, to fight in an unpredictable manner, and to be more aggressive. However, with each possible adaptive behavior, they list a negative drawback, leading the reader to believe that perhaps they don’t believe in the idea of ADHD-HI as an benefit to individual fitness.
The authors hypothesize that the individual with ADHD-HI may use their novelty-seeking and risk-taking behaviors to gain exploratory knowledge, which can be advantageous for other members of his social group (ADHD-HI, as rare as it is, is most often seen in boys). The few individuals with ADHD-HI in the social group test social limits, perform risky experiments, and explore physical space, while the reliable and predictable non-ADHD members of the social group learn from this information risk-free.
The authors demonstrate this hypothesis with a computer simulation that loosely uses the optimal diet model of foraging in hunter-gatherers. A food-changing task is used to represent a changing environment and the accuracy with which each group obtains knowledge of food quality. Four groups with 40 members each are used in the simulation: 2 homogenous groups entirely composed of either “predictable” or “unpredictable” individuals and 2 mixed groups composed of either 5% or 25% unpredictable members. The “undpredictable” members simulate the risk-taking individuals with ADHD-HI. Of the 4 groups, the one containing the 5% “unpredictable” members, or 2 members out of the 40, gained the most accurate knowledge of food quality the fastest, thus the group members died more slowly over time. In the group with all predictable individuals, members were more likely to stick to only the foods that they knew were of good quality, so members died relatively quickly over time of malnutrition. In the group with all unpredictable individuals, the members were more likely to take risks and try foods of unknown quality but did not learn from the mistakes of others, thus dying relatively quickly over time from food poisoning.
Therefore, the authors conclude that perhaps ADHD-HI was selected for via group selection, rather than individual selection, early on in hominid evolution in certain types of societies like the hunter-gatherer society, where members had to forage for foods of both known and unknown quality. This disorder perhaps persists in humans today since the cost of including an unpredictable minority in society is small compared to the cost of lacking such individuals in a rapidly changing environment.
In class we discussed how the authors didn’t really go into a detailed account of how this group selection specifically occurred, in a genetic sense. They didn’t deal with the possible problems with their group selection theory, such as how group selection would even happen when individual selection will always occur at a faster rate when conflicting selection pressures are at work. In my opinion, even though the authors did ambitiously attempt to hypothesize about a disorder of relatively unknown cause, their group selection theory was not supported with facts and was unconvincing at best.
The subjective nature of ADHD diagnoses has always bothered me a little. The DSM-IV does in fact establish diagnostic criteria for the disorder, but symptoms like “Feeling restless, often fidgeting with hands or feet, or squirming while seated,” or “Having difficulty waiting in line or taking turns” sounds like just about every kid ever. As the oldest of six, I feel relatively qualified in making that statement. I really do feel that “the ADHD issue” has a lot to do with trying to impose an educational paradigm that is no longer effective. As Sir Ken Robinson puts it, “we are getting our children through education by anesthetizing them” when we prescribe drugs like Ritalin in an effort to combat ADHD.
http://www.youtube.com/watch?v=zDZFcDGpL4U <-Changing Education Paradigms
My rather strenuous feelings aside, the notion of ADHD as an evolutionary construct is an interesting one. While I doubt that impulsivity would be as strongly selected for today as it would have been when hunting and gathering were the only way of life, it's intriguing to think that those individuals more likely to try eating that new foodsource might have been able to capitalize on that "risky" behavior. Conversely, they'd also be the first person in line to throw a spear at a mammoth… which then raises the question "How do these genes for impulsivity persist in the environment if their carriers are more likely to perform risky behaviors?"
This article presents the idea that ADHD has evolved as a trait is interesting and could have been very beneficial early on as humans were evolving. This classification of ADHD I feel would be more a societal observation and concern. As the paper stated this genetic trait could be advantageous in a nomadic lifestyle, which is what humans were at the earliest stages of our existence. By having this novel-seeking behavior it would create the chance of obtaining a new food supply, but the risks are there as well. There have been numerous studies that have focused on African tribes that have changed their lifestyle from nomadic to agricultural and the studies tend to focus on the DRD4 7 alleles in the children of the tribe. While searching for related articles on ADHD and evolutionary advantage I found an article relationship between healthy individuals and diagnosed individuals between the ages 8-16. The purpose of the article is show that when an individual with ADHD will somehow “grow-out” of the disorder and the brain will normalize by the time the individual turns 16. The article states that each individual case should be taking as such and the generalized treatment of those with ADHD should be avoided. This is stated that even though researchers have narrowed down where this disorder could come from, there are still other genetic factors and other environmental factors that can cause the occurrence of ADHD. The idea that individuals could have their brain normalize when they become odd phenomenon. This is not the first disorder that can essentially be grown out of, an example of this is asthma. Asthma has a complex network of genetic causes and other environmental factors, but if the disease is diagnosed early enough and proper steps are taken for the disease it is not uncommon for an individual to eventually grow out of the disease. Now it would be interesting to see if physicians would apply this method of individualizing treatments for those with ADHD to see the results that would happen. By prescribing different pills or a combination of pills may work for one individual with a certain level of ADHD, but may not work for those with other levels of ADHD or even people with different environmental factors with the same ADHD diagnosis. These pills have the potential to lead to more devastating side effects, such as depression. So would it be better to increase the activity level of this individuals and alter their diet to help them maintain a more modern society lifestyle than just throw a bunch of pills at them and hope they work because they had a positive effect on someone else.
Thank you both for your interesting comments. Alex, I think the information that you found about “growing out” of ADHD by the age of 16 is really interesting…I wonder if this is seen in both the inattention subtype as well as the impulsive- hyperactive subtype of ADHD? Though I didn’t mention it in my class discussion or blog summary, the authors of this paper did actually discuss this phenomenon, at least in the context of the ADHD-HI subtype. They suggest that the reduction in the ADHD-HI subtype with increasing age might have evolved because of the reduction in likelihood that disorganized experimentation at this point would result in the gathering of novel information and the increasing cost of losing the individual. This is an interesting theory anyways to a phenomenon proven through research.
I totally agree with you, as well, Nicole, about the subjective nature of the diagnoses. I think that modern-day culture plays a big part of the large 5-10% of the population diagnosed with ADHD. Kids are bombarded with constant stimulation now with the advancement of technology…they can be playing computer games while watching the hyperactive, spastic “Sponge Bob” cartoon character, fidgeting as they please all the while, yet are expected to focus on only one designated task without fidgeting while in school. School versus home life is a big culture clash, and teachers all too often tell parents that their child might possibly have ADHD. A friend of mine had her child diagnosed by a school nurse. I laughed and told her to get a second opinion, that more likely she was having adjustment issues to school.
I think a major problem of Western medicine is readiness of health professionals to blame children’s adjustment issues or emotional problems on ADHD as well. Of course, as you stated, Alex, a huge issue with Western medicine is the readiness of doctors to throw pills at children with ADHD or other disorders. A lot of these medications have not undergone long-term research studies, and, essentially, kids are being pumped full of these drugs to calm them, but at what cost? Like you said, maybe a regulated diet, or careful regulation of the environment, or even behavioral therapy, might show more favorable results.
I have never been a supporter of ADHD (at least in the masses that we see today) but this paper was intriguing since I also never understood it on the evolutionary or genetic level. I have never disagreed with the fact of ADHD existing, I just think our society has been to quick to diagnose. I really appreciated the video from Nicole, I think he hits a lot of important points. ADHD has significantly increased over the past years, highly correlated to the amount of media present in our lives. Kids and young adults have grown up with the constant entertainment and at a fast pace. What would you expect when you sit these kids in a classroom for 8 hours straight?
An interesting point that has recently been added to this argument is home life. They are now trying to correlate the single family homes, or two working parents as a lack of involvement (possibly a controversial study). Overall, many people are questioning if the lack of parent involvement or discipline is adding to a higher ADHD diagnosis. Teachers are being blamed and punished for kids not succeeding in the classroom, yet it is rare for schools to address the lack of parent involvement in the after hours…
You guys are mentioning how you can grow out of ADHD, well now there are new advertisements for adults with ADHD. How they expected that they grew out of it but they find themselves easily distracted… then the advertisement ends with a test they can take to see if they need medication. I find this really disturbing.
When diagnosing ADHD, I wonder if they include some of the evolutionary supported personality traits?