How so? Sounds like a reasonable conclusion from a simple observation to me.
most of these twins studies are garbage with methodology flaws.
This is using the same flawed BS that was used by the left for the homo twin studies.
garbage in garbage out.
The Eugenics movement called attention to parentage in determining our behaviors.
It was really just for the elite to rationalize their eliteness and the poor's poorness. Good breeding and all.