Humans did not evolve from apes. Humans and apes do share a common ancestor; however, that doesn't mean we involved from each other. The family tree just split a long time ago, humans went one way, and other primates went their way.
1. Humans ARE apes. We are one of the 5 species of Great Apes. 2. Evolution is adaptation. Apes are still around because they are perfectly adapted to their environment. So why change? 3. Go take a science class. Educate yourself.
First, your premise that humans evolved from apes is incorrect. Humans and apes evolved from a common ancestor. Second, your question implies that the evolutionary process maybe hierarchical where new species replaces the old species. This may happen, but that is not always the case. The new species may just exploit a previous unexploited niche and both species may co-exist evidence of which can be seen with wolves and coyote.