But for a certain value of biology, it is. Ki is the life force of all living things in the Dragon Ball universe, from grass and trees to dragons and gods, even androids. The biology of Dragon Ball is inextricably linked to ki and is not a natural biochemical phenomenon driving from physical laws like in the real world.
Evolution doesn't exist in Dragon Ball, at least not as the origin of peoples. There are these gods called kais that have creation power, and they're bipedal humanoids, so they made various peoples vaguely in their image.