Below is an article that appeared in the 5 November issue of New Scientist. I don't agree with all that is presented, but some points are interesting to ponder, such as why autism may have been selected for as an advantage during human history.
Could mental illness have been the making of our species? Kate Ravilious considers a controversial idea.
My dad hears voices inside his head. “Tiddles” interrupts conversations with cheerful interjections and the odd profanity. “The Bloodbeast” is more sinister, shouting at dad and instructing him to do inappropriate and socially unacceptable things. For most of his life these voices have plagued him and prevented him from living an ordinary life. I know how debilitating and stigmatising mental illness can be, so I must declare an interest in what follows.
In the industrialised world, roughly 1 person in every 25 has severe mental disorder, and nearly half of us will experience some kind of mental illness during our lives. Many conditions, including schizophrenia and bipolar disorder, as well as developmental conditions like autism, are at least in part inherited from our parents. If they affect people’s chance of survival adversely, you would expect natural selection to have eliminated them, but instead they persist at high levels.
Some argue that these genes bring benefits – mental illness and genius have a long-standing link – but archaeologist Penny Spikins at the University of York, UK, goes further. She believes that mental illness and conditions such as autism persist at such high levels because in the past they were advantageous to humanity. “I think that part of the reason Homo sapiens were so successful is because they were willing to include people with different minds in their society – people with autism or schizophrenia, for example.”
According to Spikins, human tolerance allowed the genes associated with different kinds of brain development and mental illness to flourish, kick-starting a revolution. “At some point our ancestors began to develop very complex emotions such as compassion, gratitude and admiration,” she says. “These helped them accept and tolerate people with different minds.”
By embracing the unique skills and attributes that came with unusual ways of thinking, early humans became more inventive and adaptable, and eventually outcompeted all other hominins, she says.
The archaeological evidence is circumstantial, but new findings in genetics are helping to bolster Spikin’s idea. It turns out that some genes associated with mental illness proliferated at just the time when human society was flowering and confer attributes that other hominins may not have shared. All of this raises the interesting issue of whether, in the modern world, we should place more value on people like my father.
So, when did our ancestors start to value different minds? Spikins sees the answer in some radical changes in the archaeological record (Cambridge Archaeological Journal, vol 19, p 179). Consider stone tool technology. Emerging around 2.6 million years ago, the first stone tools were crude and developments slow. For hundreds of thousands of years our ancestors made do with an array of hand axes, scrapers and thrusting spears. Then, around 100,000 years ago, there was a technological revolution, with many new and sophisticated implements appearing.
“We see a sudden change in the archaeological record to more standardised tools that are more precisely made and more technologically focused,” says Spikins. The invention of spear throwers, bows and arrows, fishing harpoons, traps and snares, for example, allowed hunters to distance themselves from their prey and so hunt more dangerous animals.
Spikins argues that this technological tool revolution may have been triggered by a greater tolerance for people with traits on the autism spectrum. “I’m not saying that someone who isn’t autistic wouldn’t understand this technology, but that the innovation is more likely to come from someone who is systematic and has a unique focus on precision,” she says. Spikins also notes that other hominins, including Neanderthals, show few signs of tool innovation and never reached the level of sophistication achieved by our ancestors.
At around the same time as the tool revolution, archaeologists see a burst of artistic creativity. This begins with things like shell and bead necklaces and decorations on bone, and later carved figurines and simple musical instruments. By about 35,000 years ago modern humans were painting stunning lifelike animals on cave walls. The striking similarity between these and the drawings produced by some autistic people with savant-like abilities has been noted by Nicholas Humphrey at the London School of Economics (Cambridge Archaeological Journal, vol 8, p 165). “This emergence of very realistic art, which is drawn with incredible precision, could be linked to the tolerance of autistic people who had those special skills within the community,” says Spikins.
Evidence of religion and spirituality also appear during this period. It has been argued that shamans were responsible for painting the cave art, and Spikins believes they would have had a big impact on society. “I think that they helped to bind people together by helping them make sense of their world, through ritual and a belief in a spirit world,” she says.
In modern hunter-gatherer societies shamans tend to be unusual and creative people, who go into trances, hear voices, hallucinate, and other manifestations of spirituality, which are all traits associated with schizophrenia.
“Using modern criteria to diagnose mental illness, I think we would say that most shamans appear to have had some form of disorder,” says David Whitley, author of Cave Paintings and the Human Spirit (Prometheus, 2009).
Anthropologist Henry Harpending at the University of Utah in Salt Lake City says Spikins idea is plausible. “The points she makes about standardised tool types and the detail in art certainly ring true.”
However, not everybody believes this. “Mental illness is more likely to be an unfortunate by-product of evolving a highly developed brain,” says Catriona Pickard from the University of Edinburgh, UK (Cambridge Archaeological Journal, vol 21, p 357).
Others argue that modern society is not a good analogue for the past. “Eccentricity is more accepted in small scale hunter-gatherer societies, as everyone has a role to play,” says Benjamin Campbell, an anthropologist at the University of Wisconsin, Milwaukee.
Genetic studies are starting to put the theory onto firmer ground. Last year’s sequencing of the Neanderthal genome showed that around 99.8 per cent of the genes were the same as those of modern humans (Science, vol 328, p 710). That is hardly surprising, given that we shared an ancestor within the past 500,000 years. But David Reich at Harvard Medical School in Boston points to some key differences. “We found that Neanderthals carried subtly different forms of the AUT2, CACP2 and NRG3 genes compared with modern humans,” he says. AUT2 and CADP2 are associated with (some forms) of autism and NRG3 with schizophrenia.
Neanderthals became extinct around 30,000 years ago, and Spikins is not alone in thinking that superior adaptability helped earlier modern humans outcompete them. Whether our ancestors were aided by having genes associated with various mental conditions is another matter, but the fact is that humans are the only hominin that survives to this day. What’s more, in recent years it has become clear that our ancestors had more contemporaries than was previously thought. Around 80,000 years ago, there were at least five species of hominin on the planet, says Chris Stringer from the Natural History Museum in London. While H.sapiens predominated in Africa and Neanderthals were dominant in western Eurasia, descendants of H.erectus still survived in Indonesia, H.floresiensis resided on the island of Flores and the newly-discovered Denisovans seem to have ranged across a good portion of Asia (New Scientist, 2 August, p34).
We don’t yet know whether early modern humans had more genes associated with mental disorder than these other species, but we may not have to wait long to find out, given the speed with which ancient DNA sequencing is progressing.
What we do know is that inherited mental disorder is extremely rare amongst living primates. Klaus-Peter Lesch at the University of Wurzburg, Germany, and colleagues looked at the gene responsible for the serotonin transporter protein SERT, which has been implicated in several inherited disorders. This gene comes in a “long” and a “short” form. Every human carries a combination of two of these. People with the long/long combination appear to be protected from very low moods, whereas those with the short/long version are more susceptible to depression, and the short/short version with emotional dysregulation. Lesch and colleagues looked at the gene in 12 species of primate and found that the short/short version is found only in humans and one other primate, rhesus monkeys. (Molecular Psychiatry, DOI:10.1038/sj.mp.4001157). “Carrying the short variant of the SERT gene seems to expose humans and rhesus monkeys to emotional disorders, which we just don’t see in other species,” says Lesch.
But the gene can also confer advantages. The short variant appears to be linked with depression in a stressful environment, but in a supportive environment people with this variant are often highly successful. “One trait that humans and rhesus monkeys share is an ability to live almost anywhere,” says Lesch. Noting that other primates thrive only in very specific niches, he speculates that behavioural traits connected with the short versions of the SERT gene may have helped both humans and rhesus monkeys to adapt to new and challenging environments.
Such adaptability would have been crucial in the past 100,000 years as our ancestors migrated around the world, and it turns out that the gene responsible for SERT is among many that evolved rapidly during this period (The 10,000 Year Explosion by Henry Harpending and Gregory Cochran, Basic Books, 2009). The genetic analysis that revealed this dramatic acceleration in human evolution also exposed the rise of another gene variant linked with mental disorder – this time one that helps regulate dopamine, the neurotransmitter associated with pleasure and reward. Harpending and colleagues found that a particular variant of the gene that codes for the D4 dopamine receptor has increased very rapidly in frequency in humans. People with this variant, known as DRD4-7R, tend to have very high energy levels and an increased risk of attention-deficit hyperactivity disorder (ADHD). Yet the prevalence of the variant among certain groups – it is found in 80% of lowland Amazonian Indians, for example – indicates that extra energy has advantages. “Previously these traits have been highly regarded in some societies,” says Lesch. “We see a higher percentage of ADHD-associated traits in migratory people, for example.
Like the SERT gene, DRD4-7R can be both a boom and a bane. Some researchers describe these as the “orchid genes”: nurture them and the carrier thrives, neglect them and a maladaptive personality trait appears. If Spikins is correct, many other genes associated with developmental conditions could possess such Jekyll-and-Hyde characteristics. Our ancestors may have benefited from this, but modern societies tend instead to view different minds as a major impediment.
“Nowadays, being different is bad,” says Whitley. “In the West, we continue to pathologies difference, and lost its potential adaptive advantage.”
Instead of ostracising people with maverick minds, perhaps we would do better to cherish them (see “Beautiful Minds?” beneath). If the special talents in the population have helped humans to get this far, we may need such different modes of thinking to see us through the next few thousand years. If the past teaches us anything, it’s that humanity thrives by being adaptable.
With the advances in genetic selection we may be soon be able to screen the genetic make-up of embryos and reduce the prevalence of conditions such as schizophrenia and autism. Could this in fact be a retrograde step?
Simon Baron-Cohen, director of the Autism Research Centre at the University of Cambridge thinks so, and not just because he considers it a form of eugenics. He believes it could also deprive humanity of some crucial attributes.
Recently, Baron-Cohen and his colleagues reported that people living and working in Eindhoven, a major information technology and industry hub in Holland, are more than twice as likely to have children with autism than those living in similar-sized Dutch cities that lack the focus on technology-based industries. (New Scientist, 22 June.)
“Our work suggests that parents of children with autism – and who therefore carry some of the genes for autism – have talents in systemising and deep focus, which has been responsible for innovation in fields like science, mathematics, music, technology, art and engineering,” he says.
Similarly, several studies have shown an apparent link between the genes associated with schizophrenia and creative ability. In 2005, Daniel Nettle from Newcastle University, UK, showed that professional poets and artists commonly possess several of the traits used to diagnose schizophrenia, such as delusions, hallucinations, moodiness and concentration problems (Journal of Research in Personality,DOI:10.1016/j.jrp.2005.09.004).
Such findings help explain why many scientists are equivocal when it comes to the possibility of genetic screening. “If we start selecting against the outer margins on any set of attributes, we may be losing something valuable for our culture in the long term,” says Robert Cook-Deegan, director of the Centre for Genome Ethics, Law and Policy at Duke University in North Carolina. “And yet the stories of suffering of those who live out on those extremes are quite real too.”
Kate Ravilious is a writer based in York, UK
Article published in New Scientist magazine, 5 November 2011, pages 35-37