Thousands of species of birds have flown the sky; how many species of humans have walked the Earth?

Most scientists agree that there have been at least 18 separate species of humans through time, including Homo habilis, Homo neanderthalensis and us—Homo sapiens. Smithsonian scientists are conducting research to learn more about how these early humans lived and why we are the only remaining humans.

Standing, hunting, cooking--how did it all begin? ›