The brothers had different fathers, but neither was told who they were. Raoul made it very clear ('I haven't got a Dad' - LT), in his last stand in Rothbury, that this was something he cared a great deal about, and, even though Angus understands that the 70s were different, that there was far more stigma about babies born out of wedlock, his fury at the situation arrives almost on the same breath.
"I feel very strongly that a child has a right to know who his father is. I don't think a selfish woman has a right to have a baby as her own plaything. I think there are massive indications there for somebody's identity in adult life. We weren't given the opportunity, for what I believe to be very selfish reasons." He has since discovered who his own father is, though he has no intention of contacting him; apparently, after all the publicity, someone has turned up claiming to be Raoul's. "I think it's a crying shame he's only turned up now Raoul's dead. It's a bit late in the day."
On Nature vs Nurture, I'm a more-or-less rather than either/or type, as in so many other things. In Steven Pinker's the Blank Slate, he posits a rough guide to how your kids will turn out, given 3 approximately* equal factors - with (I think) upbringing being the least of the three - depressing information for well-meaning daddy :
a) natural inheritance (genes)
c) post-adolescence peer group
If the third be true, it may be that yet another Sixties liberal myth (albeit one still being pumped out by our educators) is exploded - although there is a difference between childhood and adolescence, maybe being kept away from the rough boys then makes you less likely to hang with them later. Many times I've listened to or read of some successful figure describing his childhood and taking an affectionate but condescending pop at parents who wouldn't let them hang out with the rough boys down the road. Maybe that parental decision is why they're on Desert Island Discs.
When the academic Moat brother was doing politics at Nottingham, the other had discovered the society of the gym and its steroid subculture.
I don't think Raoul's background (more here) fits by any means the classic underclass scenario. But, as study after study shows, fatherless children, even after controlling for the lower income of single parents, do worse on pretty much every measure of human achievement.
As A.H. Halsey puts it in his foreword to "Families Without Fatherhood":
“The children of parents who do not follow the traditional norm (i.e. taking on personal, active and long-term responsibility for the social upbringing of the children they generate) are thereby disadvantaged in many major aspects of their chances of living a successful life. On the evidence available such children tend to die earlier, to have more mental illness, to do less well at school, to exist at a lower level of nutrition, comfort and conviviality, to suffer more unemployment, to be more prone to deviance and crime, and finally to repeat the cycle of unstable parenting from which they themselves have suffered.”
There's nothing we can do about it, though. As Sunny so perceptively pointed out a month or so back, people who have children and don't get married wouldn't be any more likely to stay together if they DID marry each other. His conclusion is that people who don't marry are just the kind of people with low commitment to the relationship, who are more likely to split (aka desert the kids), married or not !
* I think those three factors stand provided the upbringing is not 'extreme' - in which bets may be off. Obviously an infancy or childhood of torture or abuse will have a hefty effect - as will, say, being brought up in a closed religious community, or selected for the Janissaries (in both these instances your peer-group gets chosen for you as well, securing two out of three factors).