Autism’s earliest symptoms not evident in children under 6 months — Condition is characterized by a slow decline rather than an abrupt loss of skills, study says – A study of the development of autism in infants, comparing the behavior of the siblings of children diagnosed with autism to that of babies developing normally, has found that the nascent symptoms of the condition – a lack of shared eye contact, smiling and communicative babbling – are not present at 6 months, but emerge gradually and only become apparent during the latter part of the first year of life.