Well I have worked in science (as a science teacher), and I can assure you that only dolts teach evolution as a ladder. Homo erectus, etc. and modern humans have a common ancestor. The genus Homo and the genus Pan, to which chimps and bonobos belong, also have a common ancestor, but you have to go back a little further. And so on. This is the Darwinian model for evolution and it has been overwhelmingly shown to be true. Darwin's contemporary detractors tried to pin ladder-evolution on him, just as the Daily Mail would have done had Darwin been here today. At least one cartoon of the time depicted Darwin as half-monkey, half-man. Contemporary science journalism was even worse than religion when it came to misrepresenting Darwin. But Darwin never subscribed to this ridiculous ladder idea. Not once, ever.