joolstoo: most of the current thinking on brain development points to a combination of nature and nurture, with nurture as the key element (and the only one that is under the control of parents).
fairyfly: plenty of abuse happens in 'good' middle class families. i don't think anyone looking from the outside in can know what kind of parent someone is. it's totally wrong to blame the mother as abuse is generally inter-generational: people that are abused have been abused, often to a greater degree themselves.
babies that are consistently ignored never develop the capacity to empathise and in the most extreme cases have no sense of self at all and therefore cannot conceptualise the 'other'.
it's widely acknowledged that early environmental factors play a key part in deviant behaviour of most kinds.
for a simple analysis of some of the most up to date research read oliver james' 'they f*ck you up'.
if you're really interested search out the research that is extensively gone into in his footnotes.
it's very very interesting stuff: and the reason why psychotherapy and the study of brain development are coming closer and closer together.
for anyone really interested the man at the forefront of this stuff is allan schore at UCLA medical school, and a very good (if a bit sciencey) paper of his is this