The disproved notion that vaccines cause autism was born in the late 1990s, when Andrew Wakefield, a British surgeon, first went public with his idea that children could develop the disorder from getting a measles-mumps-rubella (MMR) shot. Twelve follow-up studies showed no evidence that children who had received MMR were at greater risk of autism. And yet the notion of a vaccine link didn’t die. Instead, it found safe haven in a different hypothesis: the 1999 notion that thimerosal, an ethylmercury-containing preservative, was the cause of autism. For the past decade, antivaccine groups have fought on those grounds. Science has of course stepped in to test their theories. Six studies have examined the risk of autism in those who have or have not received vaccines containing thimerosal. None found any difference. As is true with most pseudoscience, hypotheses shift, eventually settling on one that isn’t testable and, therefore, can never be proven wrong. Today, the hypothesis du jour is that autism is caused by too many vaccines given too early. In the meantime children whose parents were frightened by MMR have died from measles and those frightened by thimerosal have died from bacterial meningitis: sacrificed at the altar of poorly conceived ideas. The tragedy is, given all we now know about the neurological basis of autism, all three of these hypotheses had no chance of bearing fruit.