An article in The American Biology Teacher last month by Norman Johnson and colleagues provides useful answers for teachers to the question, "Why are chimps still chimps?"
Teachers may be posed with such questions as, If we evolved from chimps, why are there still chimps? We provide teachers with answers to this and related questions in the context of the latest genetic, fossil, and behavioral evidence. We also provide references they can use to further students' understanding of human evolution and evolution in general. In the process, we highlight recent discoveries in paleontology, molecular evolution, and comparative genomics. Modern chimps and humans shared a now extinct common ancestor that was neither a chimp nor a human in other words, humans did not evolve from chimps and, though chimps are humans' closest living relatives, we are characterized by distinct evolutionary histories.
In addition to the target audience, this article might provide an appropriate reading for undergraduates in certain contexts. The article goes well beyond the title question, including topics such as "What can we infer about chimp evolution by looking at living chimp species?".