According to a new study, on average, the variation for human traits and diseases is 49 per cent genetic and 51 per cent due to environmental factors.
Data analysis from previous studies reveals if one twin is on the autism spectrum, there is a 96% chance the other twin will also be diagnosed with ASD. However, symptom severity varies greatly between the twins. Researchers estimate genetic factors contribute to only 9% of the cause of trait variation.
The delivery method of twins may play a role in their neuropsychological development. A correlation has been discovered between twins born by cesarean section and poor cognitive development compared to twins born via virginal delivery.