This world must be different somehow, otherwise, it wouldn't be called a parallel world. The horror of the butterfly effect is that it's not only big figures who can change the world; any person, any animal, or any plant, at just the right moment, can bring about a fundamental change to the world.
Take a fish, for example. It swims in the water and could have lived a mundane life, spawned, laid eggs, and then flipped belly-up. But as luck would have it, at the divergence point of being caught and not being caught, it forms two different time branches. Assuming its possibilities split into two here, the world would then experience two different evolutionary processes: one where the fish is caught and one where it is not.
If the two outcomes make no difference, the two possibilities would merge into one, but as long as there is a divergence, a new world line is born.
Otherwise, how did the infinite multiverse come about? That's exactly how.
