Creative Mode, Normal Difficulty, Default World Type, Cheats: ON, no alterations to game rules.

For some strange reason, after breeding two turtles (without having bred anyone else) the challenge "two and two" gets marked as complete.
Before trying this, I bred a few bees in a Superflat world, and the achievement was not triggered.

EDIT: Tried this out with ocelots in a new world, and no achievement was triggered.