Did humans evolve in a straight line, one species after another?

Did humans evolve in a straight line, one species after another?

Answer: 

Human evolution, like evolution in other species, did not proceed in a straight line. Instead, a diversity of species diverged from common ancestors, like branches on a bush. Our species, Homo sapiens, is the only survivor. But there were many times in the past when several early human species lived at the same time.