I would agree, Stu, but as I say I am agreeing through ignorance, rather than knowledge. Part of the reason I was a bit cagey is that some moral conclusions are measureably different depending on how closely related to each other those concerned are. Informally this is the "family comes first" attitude. You could formulate an experiment based of the hypothesis this is to do with ensuring specific genes are passed on. I am unaware of what research of this type is being done.