Our Earth is 5 billion years old, and life has thrived here from almost the beginning. Physically we humans are mammals, warm blooded and bearing live young. The first mammals were small, seemingly insignificant creatures that coexisted with the dinosaurs. Far from being the evolutionary failures we once pictured them to be, dinosaurs ruled the Earth for 130 million years. Only their sudden, asteroid-wrought extinction allowed mammals to gain the upper hand.
Humans are primates, as are lemurs, apes, and monkeys.
The first primate was a mouse-sized creature that lived some 20 million years ago. From Africa they spread outwards in succeeding waves. By 3.6 million years ago, hominids were walking upright. At Laetoli in Tanzania, the footprints of three individuals are clearly preserved in ash. Scientists are trying to determine when hominids developed language.