I read somewhere that intelligence is just 2% genetic. I, however, find this hard to believe.
In today's day and age, when you can look up virtually anything on the net, or take an interest in anything by looking on wikipedia, or with hundreds of channels - it's just too unlikely that so many siblings seem to show a similar level of similarity.
For example - my brother and I - both very good at maths (my dad's good at maths, my mum is definetley NOT) yet we were both never particularly close with him (parents divorced when I was young) and I HATE maths, therefore never took an interest - I'm just naturally very good at it. I can't think of nay environmental factors to explain this, as we were never encouraged in anything remotely maths-y at all.
Similarly, I'm most interested in Literature, yet was never encouraged to read by my parents (I'm the only person in my family who actually reads anything.) As I say - I don't think I can put this down to environmental factors.
I can also say that I come from a very working-class, deprived area, and the only friends I have who do read books, moved up here from the South, and I've only met in my latter years of high school - so it certainly didn't come from them.