On the “atheist” vs. “agnostic” business, the old gadfly said as much as can be said, I think. From his Wikipedia entry:
As a philosopher, if I were speaking to a purely philosophic audience I should say that I ought to describe myself as an Agnostic, because I do not think that there is a conclusive argument by which one can prove that there is not a God. On the other hand, if I am to convey the right impression to the ordinary man in the street I think that I ought to say that I am an Atheist, because, when I say that I cannot prove that there is not a God, I ought to add equally that I cannot prove that there are not the Homeric gods.
If pressed, I describe myself as a “functional atheist,” living my life and thinking my thoughts, such as they are, on the assumption that there are no gods. If I can be reasonably sure that my interlocutor will know what I mean (and will not take me to be a member of that defunct rock group), or if I feel like sacrificing enough of my time to explain, I say I am a Mysterian.
Russell, incidentally, supplies a good data point to the nature side of the nature/nurture argument. His parents were radical freethinkers — scandalously so. His mother died when Russell was just two, however, and his father when he was 3½. Russell was raised by his grandmother, a puritanical Presbyterian. In adult life he was a … radical freethinker.
(Though these things are always probabilistic. Russell’s son became a stalwart of the Church of England.)