MLB second baseman aren't really born, they're mostly made out of guys who didn't quite have the tools for SS, or sometimes 3B (or, more rarely, other positions). They also have relatively short careers, relative to most other position players, because they usually have less room to lose a step (whether on offense or defense) before they fall behind the competition.
Which is not to knock Pedroia, or Utley, or any other truly great 2B.