Who will replace us?

[Clarke]

Originally Posted by Human No More

It isn't guaranteed to happen just as there might not only be one sentient species at a time. Species don't evolve towards a specific goal; evolution doesn't work like it does in pokemon.

Actually, they sort of do - the goal is to breed most effectively. Being sentient is a massive advantage in that respect, which means that any sentient species will be able to stop another from evolving in the same area. If they then start developing tools, they can easily wipe out any other sentients across the globe, since memetics is several orders of magnitude faster than biological evolution.