May I make a slight correction? Apes exist because humans didn't evolve from chimpanzees or gorillas or any other kind of modern ape. All we all evolved from an ancient ape that doesn't exist any more.
For example, human DNA is closest to chimpanzee DNA; they are our closest relatives. But that doesn't we come from chimpanzees. Rather, chimpanzees and humans are both descended from a different (extinct) species which had some chimp-like and some human-like characteristics. As that species spread into different areas, the different groups faced different environmental challenges - climate, food, predation, etc. which brought out latent characteristics more strongly.
Perhaps there were genes in the population for really stocky individuals, but genes were also present for really thin individuals; if one group spread into a very frigid area, the group would have specialized to heavier body types - heavier individuals survived better and so passed their heavy genes on to their children, so that in time the thin genes would pass away or become very rare. Another group may simultaneously spread into a hotter climate, and in that population the thinner individuals would have survived better, so over time the entire population would become thinner.
Sometimes, the population groups have some contact, so interbreeding keeps them from becoming differnt species. In that case (like in ethnic groups of people) every population group retains almost all the genetic traits possible. For example, Chinese are on average ont he shorter end of the human scale, yet it isn't that hard to find a very tall Asian person because they are still human - they still have all the possible genes inside. But you can't get a blue whale that has killer whale coloring; they have been separate long enough that their differences are too great for them to breed. They are different species.
By about 50,000 years ago the differences between humans and chimps was enough that humans represented a different species from any of the apes. Climate changes forced our anscestors out of the trees into the savannah, and upright walking was needed to survive. Our farther anscestors may have gone further into the jungle, higher into the mountains, etc. and adapted to the climate there, becoming chimps. I don't know for sure.
You deifinitely have the idea; this question you refer to is invalid. And your point that clear evidence exists demonstrating the connection from humans to other primates is good too.