This is right, calves are mostly genetics. And whoever said that they are mostly fast twitch fibers is INCORRECT. Like Gjohnson said correctly they are mostly slow twitch fibers. People that have more fast twitch in their calves are the ones that can make them grow. I am one of the lucky "white" guys that could run fast and jump high with the brothers, hence more fast twitch muscle fibers in my calves. People of African decent, Italian decent and German\Austrian decent in general have more fast twitch fibers than other racial groups.
Thats generally true but you you guys have awesome genetics overall thats probaly one body part your generally weak in but so are most people in general. Also its more of a structure thing than a lack of fast twitch in black guys, your tie ins dont run as low.