The earliest hominins
The story of our lineage begins in Africa, with ancestors who walked upright long before their brains grew large.
Walking upright
Bipedalism, walking on two legs, is the defining early hominin trait. It shows up in the skeleton: a skull opening (foramen magnum) positioned underneath, an S-shaped spine, a bowl-shaped pelvis, and angled thigh bones. Fossil footprints at Laetoli in Tanzania, about 3.6 million years old, show upright walking clearly.
Australopithecus
Australopithecines lived in Africa from about 4 to 2 million years ago. The famous fossil 'Lucy', an Australopithecus afarensis about 3.2 million years old, was bipedal but had a small, ape-sized brain and long arms suited to climbing. Bipedalism therefore came long before large brains.
Why upright walking?
Hypotheses include freeing the hands to carry food and infants, seeing over tall grass, and saving energy when travelling between patches of forest as African climates became drier and more open. These explanations are not mutually exclusive, and evidence is still debated.
Flashcard
Habitual walking on two legs
Check your understanding
The fossil 'Lucy' shows that early hominins: