How did the definition of autism change, from Kanner and Asperger to one spectrum?

Autism was first described as a pattern in children in the early 1940s, and its definition has widened step by step since then. Leo Kanner, working in Baltimore, reported eleven children in 1943. Hans Asperger, in Vienna, wrote about a similar group, and his thesis was published in 1944. For decades they were described by separate names. In 2013 the American diagnostic manual, DSM-5, folded Asperger syndrome and infantile autism into one category, autism spectrum disorder.

The earlier history is older and stranger. Eugen Bleuler coined "autism" in 1911 for a symptom of schizophrenia, and autistic children were often diagnosed with childhood schizophrenia. Grunya Sukhareva's studies from the 1920s are the earliest to focus on children we would now call autistic. Kanner first met Donald Triplett in 1938, and later said this was the first time he saw the pattern of autism. Nearly all the features he described, such as "autistic aloneness" and "insistence on sameness", are still regarded as typical.

A turning point came around 1980, when autism was recognised as distinct from schizophrenia. In 1979 Lorna Wing and Judith Gould coined the phrase "autism spectrum", and Wing's 1981 paper greatly increased awareness of Asperger's work, which had been almost unknown outside the German-speaking world. The definition has kept moving: some researchers now call the single spectrum overly inclusionary and suggest distinguishing people who need continuous assistance. That is a live debate, not a settled answer.