Robin williams was/is a psychiatrist who wrote 'Families and How to Survive them' with John Cleese,or vice versa.
As part of his introduction for groups of would-be psychiatrists,he tells them-at this point they do not know each other-to wander around the other people in the group without talking .
After a while they stop,and he asks them to name people they feel they could spend the rest of their lives with-I suppose within the context of the excercise.These people then go off and talk about themselves to each other to find similarities and differences in who they are,and who their families are.
He has carried out this excercise often.He says that invariably people in the groups with similar family backgrounds choose each other,and also says that there are individuals who choose no-one,and these people are orphans.
I suppose different things can be extrapolated.
My take on this is that genes manifest themselves in some way in the macro world of human beings,and at some level the human organism can recognise these manifestations.And also that the human behaviour can be manifestations of genetic organisation.And further,that human behaviours,to a greater or lesser extent,are an expression of stable genetic organisation,and are therefore an instrument for genetic organisation.