One of the leading arguments many evolution critics propose is:
If humans descended from apes, why are there still apes?!
This question demonstrates the lack of understanding many evolution-deniers have about evolutionary thinking. Firstly, that is not how evolution works; we did not descend from apes, we share a common ancestor with apes. If you trace back the lineage of humans and of modern apes you will discover that the two lines eventually converge (after many, many generations) to a single point; this point is our most recent common ancestor. Due to reproductive barriers and decreased interbreeding, offspring of this common ancestor became reproductively isolated from each other. These two separated groups then diverged and followed separate evolutionary pathways; one group became modern apes, and the other became humans. This common ancestor, who lived about 6 million years ago, did probably look more like a modern ape than a human – but she was neither a modern ape nor a human. Track the lineage back in time, and you will observe that no species ever gave birth to a member of a different species. No ape-mother ever gave birth to human-offspring. This is a gradual process that can only truly be appreciated in retrospect. Only after enough adaptations have accumulated can we distinctly separate members of the two lineages.
Diversification of life is not a linear process where one species turns into another. Rather, It is a more complicated process where species branch off from a shared ancestor. If it were a linear process, without branching, there would only be one species alive at a time. If you were to follow the train of thought of this (human-biased) question: Prokaryotes would have been completely superseded by simple Eukaryotes, which would all evolve into sponges, which in turn would go extinct and become fish, which would all turn into amphibians – and so on, all the way until humans were the only species of life on earth. The diversity of life we observe today derives from the branching off of species from ancestral lines. The process is not a waterfall where tens of thousands of ancestral apes reached some figurative “cliff” and began giving birth to humans. It looks more like a V-shape, where the common ancestor is at the bottom, humans are at the end of one line, and bonobos / modern chimpanzees at the end of the other. Apes are our cousins, not our grandparents.