The split is really 3 ways, nature/nurture/noise, although the latter two tend to get lumped together and called nurture. The rule of thumb for most complex tr

The split is really 3 ways, nature/nurture/noise, although the latter two tend to get lumped together and called nurture. The rule of thumb for most complex traits is half genetic, half environment... but this half is almost all "un-shared environment", meaning things specific to the individual (possibly random), not "shared environment" meaning observable things like parents, diet, schools, typically shared between siblings. I don't know the numbers for autism, but would guess it's like this. Which is to say, be careful how you read statements that nurture plays a role -- it's often written to mean "not-nature", and but read to mean "upbringing".