For example, in brotherhoods, fraternal organizations, sororities, locutions like "the family of man, " you try to get people who are not related to use the relationship type that would ordinarily be appropriate to close kin.
It is not that genes account for all of the risk for autism, but yet they account for a lot of that risk, because when you look at fraternal twins, that concordance rate is only 31 percent.
On the other hand, there is a difference between those fraternal twins and the siblings, suggesting that there are common exposures for those fraternal twins that may not be shared as commonly with siblings alone.