Lewis-Clack doesn’t talk much, responding to most questions with short sentences. “I crack the eggs,” he amiably offers when asked how he’ll help his mom prepare a pumpkin pie for the holidays. He communicates mostly through his music: He played in his first concert at age 7 and now travels around the world to perform in fundraisers to benefit people with disabilities. Because of his exceptional musical talent and his intellectual disability, he is considered a savant—one of those unusual people who struggles with tasks that most people find simple, yet has extraordinary abilities that few could hope to attain.

Savant syndrome is a loose term that refers to people who have a combination of significant cognitive difficulties, often stemming from autism, and profound skills—“islands of genius,” in the words of Wisconsin-based psychiatrist Darold Treffert, an independent scholar who has studied savants for more than half a century. Once thought to be rare in people with autism, found in no more than 1 out of 10 individuals, research over the past few years suggests savantism may be more common: As many as one in three people with autism may possess exceptional abilities.

Exactly how and why savantism happens is unclear. But some evidence suggests that savants may have experienced an undetected injury to the left hemisphere of their brain in utero or in infancy, triggering compensatory recruitment in the right brain that unleashes unusual abilities.

Most savants have special abilities in musical, artistic, mathematical, or mechanical domains, coupled with extraordinary memory. Stephen Wiltshire, for instance, a British savant and artist who was diagnosed with autism at age 3, has been called a “human camera” because of his ability to draw landscapes from memory after seeing them only once. Other savants possess the uncanny skill of ‘calendar calculating’—quickly computing the day of the week of any arbitrary date in the past or future—highlighted in the 1988 Oscar-winning movie “Rain Man.” Still others may have a facility with foreign languages, the ability to measure distances or heights with precision without using instruments, or exceptional map-reading skills. But only a handful possess Lewis-Clack’s extraordinary gift.

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Savants were described in the medical literature as early as the late 18th century, but the past few decades have provided a better understanding of the phenomenon. An extensive survey in 1978 suggested the 1 in 10 estimate, and it became an article of faith.

But research in the past 10 years has generated some controversy about the actual incidence of savantism. Some researchers say these seemingly extraordinary abilities may just reflect the fact that many people with autism have a different skill set than their typical peers do. “People with autism are natural specialists—when they dig in, they quickly become expert,” says Laurent Mottron, a psychiatrist at the University of Montreal.