Well maybe I am making an assumption but I figured that the ape experienced the same environment changes as man did and I would have expected at least some changes over the same time period. I also thought that man and ape had about the same abilities at one time. When man changed so many times while the ape never changed I find that confusing.
Look, it only takes one mutated ape (or ape ancestor) to start the ball rolling toward getting a small population of slightly different creatures, living with the originals. They move away and they form their own breeding population, which in time, after perhaps numerous further mutations, becomes a species different from the ancestral stock. Now you have two species. The originals haven't changed. No one individual has changed, but you now have a new species. Repeat. Repeat again. That's how it works.