Chucky are you in the field then?
I only read the first sentence, but it seems to take an eyesenk view of the disorder.
He also believed that introversion and extroversion were also linked to the Limbic system and the ARAS. Although I thought his research was shown to be quite flimsy in the end.
Ohh can't you tell I just sat a psych exam hehe

I had to write about Eyesenk.
I definitely think there is a biological basis for BPD, a chemical/biological/genetic vulnerability to the illness if you like, which it is possible to overcome in the right "nuturing" environment, however if invalidation occurs too it can exascerbate / cause the actual illness to take hold. But everything is just theory when it comes to such a thing.
I think that would explain why some people have similar experiences and dont get BPD and why some people have a great childhood and still get it. 2 different (or many different) factors at play.
J