1) Fossil discoveries have shown that human-like creatures lived hundreds of thousands to millions of years ago, but the exact origins of humans is still unclear. 2) Early hominids such as Sahelanthropus tchadensis from 6.75 million years ago may have been human ancestors or more closely related to other apes. 3) Over millions of years, hominids became more upright, less dependent on trees, developed tools and art, and migrated from Africa to other parts of the world, including Neanderthals who lived in caves. 4) While theories abound, the exact reasons for hominid migrations and developments are unknown.