Autism—like multiple personality and child abuse—was considered extremely rare, but is now known to be relatively common, including brilliant people.

One of the most ignorant arguments against the validity of multiple personality is that it went from being thought extremely rare to being found relatively common, which, supposedly, is impossible.

Child abuse—which, before 1970, was thought to affect only one child in a million, but is now known to affect upwards of one child in a hundred—is one thing that disproves that argument; autism is another.

Reviewed in today’s Wall Street Journal by Richard J. McNally, “In a Different Key: The Story of Autism” by John Donvan and Caren Zucker, “tells a riveting tale about how a seemingly rare childhood disorder became a salient fixture in our cultural landscape…

“The prevalence of autism has risen markedly in recent years, climbing from a rate of 4 to 5 cases per 10,000 people in 1966 to approximately 1 per 100 ‘on the spectrum’ today…

“Early work on autism concerned markedly impaired children, most of whom had severe intellectual disabilities…But high-functioning people…led to the rediscovery of work by the Austrian pediatrician Hans Asperger, who in 1944 had described youngsters with autistic traits whose intelligence was normal or superior. Some exhibited brilliance…”

Autism and multiple personality are unrelated, except that both went from being thought extremely rare and always dysfunctional to being found relatively common and often advantageous.