Mental Problems Gave Early Humans An Edge

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.

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 that 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. 

Others argue that modern society is not a good analogue for the past. "Eccentricity is much 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. He is supportive of Spikins's idea and agrees that complex emotions such as compassion set us apart from other species. "Modern humans understand that someone else has different thoughts, and we have developed this ability to a tremendous extent," he says. For sure, the archaeological evidence is circumstantial, but genetic studies are starting to put the theory on 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 AUTS2, CADPS2 and NRG3 genes compared with modern humans," he says. AUTS2 and CADPS2 are associated with autism and NRG3 with schizophrenia. However, Reich adds, it is not clear whether these differences influenced the way our ancestors thought.

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