Nuerodiversity as an inevitable outcome of social evolution

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So I have a thought about the prevalence of PDDs and other neurotypes like ADHD, especially in recent years, and basically want to find a way of putting the idea of neurodiversity in quantifiable terms

There are limits to the development of mental capacity, which humanity has long since reached

It's very tempting to think that you can continuously cram processing power into the brain of an individual and you'll get a higher and higher qualitative mental output as a result. It has seemed to work that with human evolution in the past, as our ancestors progressively acquired larger and more complex brains that allowed them to process more information than any of their counterparts. Looking at the development of artificial processing systems, things like Moore's law would seem to suggest similar results.

But ultimately, this belief doesn't pan out, or at least hasn't panned out historically. Looking at the evolution of the species, the sapient brain would seem to have peaked tens of thousands of years ago. Evidence would even suggest that our cousins, the Neanderthal, actually possessed a brain of comparable or perhaps even greater processing power than that of ourselves. It can of course be argued that the apparent stagnation in the development of human mental capacity is coincidental, as people don't necessarily reproduce on the basis of brain power, we can generally assume that the ability to process information did at least aid in survival during an age when man was making great strides in developing tools for hunting, self maintenance, and comfort.

Thinking about it logically, it only makes sense that mankind would eventually reach a plateau in mental development eventually. In optimal conditions each additional piece of information we acquire should logically have a value less than the information acquired before it. Mathematically, this would make the benefits of mental capacity a geometric series with a rate less than one, which converges to a finite sum even if it could hypothetically go towards infinity. Conversely, the costs of mental capacity increase at an accelerating rate, because assuming the cost of maintaining a link between neurons or any other type of processing unit remains fairly constant, the number of links increases dramatically with each addition processing unit, as they should have to integrate with every other unit which was there before hand (in computer science, this is basically the problem of tractability). So mathematically we can think of the costs as increasing in a manner best represent by a factorial, which becomes larger at an accelerating rate as the base value of the variable goes towards infinity.

To put this into a numerical representation:



But to put it in even simpler terms, there are no free lunches. Instead of being able to build up processing power of the human brain towards infinity, you tend to reach a peak at some point. Also, since the number our neurons and processing units range in the billions, the resulting change to the cost/benefits ratio is relatively small for the relatively variations of processing power that result from the intergenerational changes in the number of neurons or other faculties that allow the brain to process information only cause a relatively small change in the value of the output, and is certainly overwhelmed by the other factors such as how one is educated and so forth.

Human society counteracts this barrier

Since we can now take it as a given that we've more or less reached a plateau as to our mental capacity, we need to ask how humanity has clearly surpassed its ancestors as to the amount of information it handles. The simple answer is that we're able to do so through the complex mechanisms of human society. Economic phenomena like specialization and increasing returns to scale allow humans, by working together, to build systems of incredibly more value than the sum of its parts.

It's worth noting that we have, in fact, been evolving for thousands of years to adapt to our own human society. By sacrificing things like genetic memory and certain biological instincts, we've acquired the capacity to learn things from one another to a much greater degree than any other animal. In fact, it's gone so far that, without human society, we would be completely unable to survive.

Getting around to the point of where our different neurotypes works into all of this, in early human civilization, people faces relatively similar circumstances, did jobs that were more similar to each other than not, communication was limited largely to speech and nonverbal physical cues, and learning from others was by and large done through the sort of monkey see monkey do mechanisms that things like mirror neurons tend to enable people to do. In other words, it would have been a very bad time to be autistic a few hundred years ago. So, predictably, people tended to evolve towards the neurotypical formulation that most people have today.

I made a graphical representation of this point here.



The X axis in this representation represents the different types of information, with two points on the x axis that are relatively close together representing information that is more closely related to one another than a point which is farther away. The Y axis represents the depth of understanding of a given topic, with the high a point is, the more deeply a topic is understood. The different curves represent different neurotypes, with the teal one representing a neurotypical mindset, the green line representing a mindset like autism which tends to lend itself to highly specialized knowledge, while the blue line represents a mindset that lends itself to knowledge over a very broad range of topics, like one might see neurotypes like ADHD as being. The area under each of these curves represents the amount of information that people of each neurotype can process, which is practically equal for all different neurotypes.

The Dark red line here represents the range of information processesing which is necessary to thrive within society and reproduce at roughly the average. Areas where the line is above the different nuerotype curves represents areas in which each neurotype is deficient, and the pink shaded areas represent the magnitude of social maladjustment that subsequently results. This model represents the setup which has previously existed in neurological distributions, with only the nuerotypical curve being able to fully clear the dark red curve and avoid significant degrees of maladjustment.

Society is becoming more complex, opening the way for more neurodiversity

Society, as it has developed, has become increasingly more complex at an accelerating rate. Now the types of work people tend to do can differ dramatically, at least compared to relatively recently when most people were farmers or factory workers. Now people need to possess different means of problem solving and thinking to do well in their jobs than they did in the past, or would need if they were working in any other kind of job. If you work in research and development, you need to be able to grasp abstract concepts in order to do well. In contrast, if you work in finance, you need to be able to take a large variety of factors that are constantly changing in a timely manner. Likewise, it's become possible for people to communicate in drastically different ways, whether through writing, using the internet or computers, or even things like art work or music to convey messages and interact with other people. It's become possible for people of varied neurotypes to get by, but also thrive in this environment.

This new setup can be similarly graphically represented



The set up is by and large the same as the one which existed previously. The one difference is that now the red curve representing the basic level of knowledgeably and skills required thrive within society has shifted downwards as a result of the increasingly varied settings people now can choose from, and the number of different capabilities now available to people of different neurotypes which allows them to overcome their previous shortcomings. Note that now each neurotype lies above the red line, meaning now everyone can live relatively free of social maladjustment. Also note that, because different neurotypes are available, a much greater depth of understanding on a much broader range of topics is now available to society, with this additional output represented by the yellow shaded areas. Also note that in this setup, each different neurotype continues to make their own unique contributions.

I think that increased neurodiversity is virtually inevitable and desirable on the course we're on. Humans have reached an upper limit as to how much information they can process, but they need to process more and more complex functions to drive development and advancement. By utilizing various different mental formulations, we can overcome the limitations which have hindered us in the past. People can become better adapted to the types of problems they are asked to solve.

Last edited by smalls on 11 Apr 2008, 4:10 pm, edited 4 times in total.

If we want to open up another evolutionary thread, I think that it's more a matter of autism being a leftover genetic trait from some of our less sociable ancestors than some sort of "next step". Our non-pack anscestors didn't need to rely heavily on communication or recognize faces (or more likely scents) so they processed other members of their own species as objects.

We see strange things pop up in the population from time-to-time like webbed feet or a tail. It's weird and freakish, but it still occassionally pops up as a matter of genetics because the data never completely goes away, even if it no longer serves a purpose. Autism can be looked at the same way, except that those on the higher functioning end of the spectrum, even if they have a lower chance of reproducing themselves, hold certain advantages for the success of the "village" which keeps their genetic material within the population in an indirect way.

This, in turn, keeps the spectrum more alive within the general population than other non-adaptive traits.

I would tend to disagree. Mainly, the whole autistic neurotype encompasses a wide variety of traits that could potentially come from any number of different sources, whether as a dormant/recessive gene inherited from ancestors, or spontaneously generated through the quirks of genetic mutation. I would say the same of ADHD and any other number of different neurotypes that affect learning and problem solving. But I think that's somewhat besides the point because the combination of traits within these neurotypes are unique. Less mirror neurons might be inherited from our less social ancestors, but an enhanced ability to grasp abstract concepts or recognize patterns is probably not, as they would not necessarily have benefited our ancestors enough to have been a dominant trait at that time. So I think that the increased prevalence of varied neurotypes is something unique to the present day.

I also want to clarify that i'm not saying there is a definitive next step in terms of human evolution. On the contrary, I think that we're developing along many divergent courses, with autism being one of them. Typical neurotypes are going to have as much usage as they have ever had, theres just more room now for more varied neurotypes to thrive too. I also think that, even if there are still barriers that make a person with a unique neurotype less likely to reproduce, that gap would seem to be rapidly closing, so I think some demographic changes are not only foreseeable, but already in the process of happening.

Last edited by smalls on 11 Apr 2008, 11:41 am, edited 1 time in total.

Ah, but you're missing that the two are in the same package. Our ancestors may have developed the traits for their non-social aspects and got a useless increase in abstract thought as a part of the package. Since an increase in abstract thought is not maladaptive, no harm happens and the species flourishes.

Fast forward a couple milenia and humans have evolved into a social species and the non-social traits are dying out. However, an increase in abstract thought is suddenly a highly adaptive trait leading to sociatal success. So the lost traits continue to manifest themselves. This time though, there is no free lunch and non-social traits ARE maladaptive, especially in cases where the trait manifests fully. As such only a small fraction of the population develop the trait.

If we were just looking for an increase in abstract thought and spontaneously evolved the autism spectrum, why all these unnecessary and maladaptive traits? Evolutionarily that doesn't make sense. It only makes sense if these traits WERE adaptive at one point.

But here's the thing. Within Autism, the two things tend to come within the same package, but that doesn't mean that the traits themselves must necessarily come together. Lack of mirror neurons and enhanced abstract logic may frequently come bundled together, and they may compliment each other. But that doesn't mean that those two traits automatically come together.


But in order to assume that, we have to accept that our ancestors had a penchant for abstract logic. Now keep in mind that, to go to a time before social interaction became a factor in our evolution, we would have to go significantly far back to ancestors whose mental capacities were considerably different than our own. It's more likely that our ancestors simply didn't possess the various traits of enhanced pattern recognition and abstract logic because at a time when most of the issues affecting survival were those physically and immediately before them, those things never offered much of an advantage, so there's no reason to believe that they were prevalent within the population.


The point i'm trying to make here is that these non-social traits, or at least altered social traits, are increasingly less maladaptive, the other cognitive traits are more advantageous to have, in certain circumstances. This all has the net result of a distinctive out branching of alternate neurotypes which don't just pop up randomly from time to time via recessive genes, but are actually able to thrive on their own terms, and become a larger factor within society at large.

I bow before this speech

thanks .

I also added some additional charts to provide a somewhat clearer (though simplified) illustration of how I view this topic