Different Minds

New Scientist Nov. 5, 2011 (my favorite magazine)

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.

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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.


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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.

Double-edged sword
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.

BEAUTIFUL MINDS?
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


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