Larger brains

Developing a larger brain

Three million years ago, our ancestors’ brains were only about the size of a modern chimpanzee’s brain.

• brain size of Australopithecus afarensis: 450 cubic centimetres (cc) (1.3 per cent of their body weight).

Around two million years ago, our ancestors’ brains began to dramatically increase in size and the braincase began to expand.

• brain size of Homo habilis: 610 cc (1.7 per cent of their body weight).
• brain size of Homo ergaster: 860 cc (1.6 per cent of their body weight).

600,000 years ago:

• brain size of Homo heidelbergensis: 1250 cc (1.9 per cent of their body weight).

Our brains are now three times larger than those of our early ancestors and we have a large braincase with a tall forehead.

• brain size of Homo sapiens: 1350 cc (2.2 per cent of our body weight).

Comparing then to now

Seven million years ago

Seven million years ago, our ancestors’ brains were similar to those of modern chimpanzees.

Brain size:

• brain was small (about 450 cubic centimetres), representing approximately one per cent of the body’s weight

Skull shape:

• cranium was low and narrow
• there was no forehead
• skull had a deep post orbital constriction (narrowing of the skull behind the eye sockets)

Now

The evolution of modern humans has involved a significant increase in brain size along with a re-shaping of the skull in order to fit this larger brain.

Brain size:

• brain is large (about 1350 cubic centimetres) and represents more than two per cent of the body’s weight

Skull shape:

• braincase is high and wide
• forehead is high
• skull is expanded behind the eye sockets