I've done a lot of family history and got in touch with a 4th cousin. Our common ancestor was born in 1824 and died in 1889. The two families seem to have stayed in touch until about 1950 shortly before my great grandmothers death.
What is really striking is the similar patterns the two families, which knew nothing about each other, have seemed to have taken. There are common interests and occupations. And even some personality traits.
My father's cousin also lost touch when his mother moved to South Africa when she was 2 and died shortly after - and again a similar thing - despite him not being raised by his biological mother.
There are also traits that seem to follow through for generations in my husbands family.
I think it likely that it is a social and biological related thing and not one rather than the other. I think there is a certain amount of predetermined fate about the life you end up living.
However its also very clear that particularly significant events or twist of fortune can have very profound effects for generations. One person becoming an alcoholic or having a husband die can change everything, not just for an adult, but their child and their grandchildren and great grandchildren before there might be an opportunity to recover from that incident.
So blank slatism? No. I think it's far harder to escape the reality of your birth than many of us would like. Some people can and do manage it, but I think it rarer and harder than we care to think.