Human evolution

Humans evolved by natural selection over millions of years, like every other species. Fossils of our ancestors, the stone tools they made and the DNA of living people all give evidence for how and where this happened. The evidence shows that walking upright came first, and large brains later, and that modern humans first appeared in Africa.

Key facts

• Ardi (Ardipithecus ramidus), about 4.4 million years old, had a big toe that could grasp for climbing and long arms, but walked upright; its brain was about the size of a chimpanzee’s.
• Lucy (Australopithecus afarensis), about 3.2 million years old, walked upright on feet more like a human’s, and had a slightly larger brain.
• Turkana Boy (Homo erectus), about 1.6 million years old, found by Richard Leakey’s team, had shorter arms and longer legs, much more like a modern human, and a much larger brain.
• Stone tools became more complex: Homo habilis made simple pebble tools; Homo erectus shaped hand axes; Neanderthals made more complex flint tools and wooden spears; Homo sapiens made fine flint tools, arrowheads and needles.
• Tools and fossils are dated by stratigraphy (deeper rock layers are usually older), by dating the volcanic rock layers around them, and by carbon-14 dating for remains up to about 50,000 years old.
• Skeletons show walking upright (bipedalism): the foramen magnum is under the skull, the spine is S-shaped, the pelvis is short and wide, and the big toe is in line with the other toes.
• DNA shows that humans and chimpanzees share a recent common ancestor. Fossils and DNA support the “Out of Africa” hypothesis: modern humans first evolved in Africa and later spread across the world.

Worked examples