How do you evolve without going extinct?
Some people think that over the course of several million years, Australopithecus became Homo habilis resulting later in us. For this to happen the embryos of this organism would have to remain viable, allowing the organism to develop into an adult stage. I'm not sure why anyone believes millions of years of evolution via natural selection pressures will achieve this. When you try to simulate the embryo evolution over hundreds of millions of years on a computer, or just do the math with a pencil, the embryos always die, so they do not even make it to early development, let alone adulthood, so why would you think they could do it over a few million years?
If you try to do this in a lab with a real embryo, I don't think anyone's ever seen a similar thing happen with living apes. It seems like the simplest explanation is that chimpanzees and humans don't actually have a common ancestor, and they were simply always around, or if there were some phenotypic changes due to natural selection, they were small.