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Could Asperger's really be a legacy of the Neanderthals?

Neanderthals Asperger 2

There are many theories for the causes of conditions like Asperger's, ADHD or Tourette. A controversial but intriguing theory called the Neanderthal theory of autism offers a unique perspective of this neurodiversity as a fully functional human variation.

The Neanderthals (Homo Neanderthalensis) are our closest human relatives and lived in Eurasia 200.000 to 30.000 years ago. Their appearance was similar to ours, though they were shorter and stockier with angled cheekbones, prominent brow ridges, and wide noses. Though sometimes thought of as dumb brutes, scientists have discovered that they used tools and art, were familiar with language and symbols, buried their dead and controlled fire.

More information: Human origins: Not that simple

Genome sequences harvested from Neanderthal bones have recently confirmed that modern humans (Homo Sapiens) and Neanderthals mated, and that 1% to 4% of the genomes of people who descend from Europeans, Asians and other non-Africans is Neanderthal. This crossbreeding went on for several thousands of years during the period when modern humans from Africa were (re)-populating the world around 40.000 years ago, until the Neanderthals disappeared from the scene.

Their genes probably helped us adapt to the colder climates in the north but according to the Neanderthal theory of autism, those genetic influences also manifest as autistic traits. The name itself might be a bit unfortunate though, because the theory seems to apply to phenomena like Asperger's better than to autism, which is a developmental disorder rather than a neurological condition. Moreover, the hypothesis is far from proven and one of the first questions you might ask is: as sub-Saharan Africans don't have Neanderthal DNA, is Asperger's less common in them than it is in Europeans?

Although comprehensive data is lacking the answer seems to be: Yes indeed it is. As John Elder Robison, author of the 2007 memoir "Look Me in the Eye" writes on his blog: "I’ve made over 100 public appearances and spoken to some thousands of people who have a personal stake in Asperger’s or autism. One interesting point stands out. The number of black Aspergians I’ve met can be counted on one or possibly two hands."

That statement might sound a little bit suggestive, but in 2011 a study was done in Sweden which specifically looked at risk factors for autism and Asperger's in relation to perinatal factors and migration. Among children of women who were born in sub-Saharan Africa only 1 case of Asperger's was recorded, but the risk for autism was found to be relatively high with 11 cases found. Among Europeans, in contrary, Asperger's and autism were much more evenly spread.

People with ASD differ from each other just as much as anyone else, and their condition should not be seen as a disability, but rather as another way of functioning. It's more common in boys and is usually characterized by the ability to focus on one interest or task, along with little flexibility for change and a high sensitivity to stress.

There's a different development towards adulthood, which leads to being ahead of age when it comes to cognitive skills, but lagging behind in social and emotional terms. The level of intelligence is normal, but IQ tests may show a disharmonic profile, which means being very good at one thing but really bad at another.

More information: Balancing your empathy

Despite a normal development of language there are severe difficulties in social interaction which often lead to exclusion and rejection, which may in turn give rise to depression and other mental problems. The use of language is sometimes peculiar and words or remarks are often taken literally, while non-verbal communication poses difficulties.

This might be caused by a different way of using "theory of mind" or "cognitive empathy." In order to have an efficient and satisfactory conversation, people continuously form a (subconscious) image in their minds of what the person they're talking to might be thinking and feeling. In the case of autistic spectrum, this system doesn't work as quickly, or might get overloaded by all the signals, many times contradictory and confusing, that we are constantly broadcasting when having a conversation.

The big question is wether any of those features can be traced to the Neanderthals. Unfortunately, there is no group of ancient Neanderthals left in some remote area of the planet, so that scientists could obtain direct knowledge of the way they interacted with each other. Therefore the Neanderthal autism theory remains interesting, but highly speculative.

On the other hand, looking at a Neanderthal skull with its large space for the nose, it's not hard to imagine that they might have had a better sense of smell, just like Aspergers have. Their heads were also bigger than those of modern humans, which could indicate a very good memory, a property Aspergers are known for as well. However, bigger brains come with a price wich is larger internal distances to be bridged by the neurons, possibly resulting in less interconnectivity within the brain.

To determine whether the Neanderthal theory of autism is valid, research to identify Aspergers genes and find out when and how those genes developed in humans would have to be done. Meanwhile, we should regard ASD as part of the diversity that nature needs, to make this beautiful world we live in.

 Image credit: NASA/JPL-Caltech