Autism is a developmental disorder characterized by troubles with social interaction and communication, and by restricted and repetitive behavior. Parents usually notice signs in the first two or three years of their child's life. These signs often develop gradually, though some children with autism reach their developmental milestones at a normal pace and then worsen.
Understanding is a psychological process related to an abstract or physical object, such as a person, situation, or message whereby one is able to think about it and use concepts to deal adequately with that object. Understanding is a relation between the knower and an object of understanding. Understanding implies abilities and dispositions with respect to an object of knowledge that are sufficient to support intelligent behaviour.
If by some magic, autism had been eradicated from the face of the earth, then men would still be socializing in front of a wood fire at the entrance to a cave.
Temple Grandin, Thinking in Pictures: My Life with Autism (2006).