It had long been presumed that there is a common cause at the genetic, cognitive, and neural levels for the social and non-social components of autism's symptoms, described as a triad in the classic autism criteria.However, there is increasing suspicion that autism is instead a complex disorder whose core aspects have distinct causes that often co-occur. While it is unlikely that a single cause for ASD exists, many risk factors identified in the research literature may contribute to ASD development. These risk factors include genetics, prenatal and perinatal factors (meaning factors during pregnancy or very early infancy), neuroanatomical abnormalities, and environmental factors. It is possible to identify general risk factors, but much more difficult to pinpoint specific factors. Given the current state of knowledge, prediction can only be of a global nature and therefore requires the use of general markers.