Clearly both heredity and lifestyle are important. My father, my mother's father and my mother's brother all died of stroke at ages younger than my present age (60); which suggests that I have dreadful genes. But when my GP invited me for a general check-up three years ago (not because of my family history, the practice does it for everyone at certain ages), all my parameters were found to be completely normal.

None of the above relatives ran or cycled regularly like I do (although apparently my father did some boxing in his youth). My father smoked, and my grandfather wouldn't eat his vegetables (so my mother once told me; he died when she was just 9). Maybe my lifestyle has counteracted my bad genes, or maybe it is simply that I haven't inherited bad habits.