Researchers at an archaeological site in Georgia have discovered an early human skull with unusually small brain cavities.

The small, lightly built hominid had a short nose and huge canine teeth.

A BBC Science correspondent says the discovery has called into question the theory that our ancestors migrated out of Africa as their brains became larger, enabling them to adapt to new environments.

The skull, the third to be found at the site, is thought to belong to the species Homo erectus, but it is much smaller than the others.

All three are around 1.75 million years old.

The small skull probably had a brain of about 600 cubic centimetres, while the others would have been about 800 cubic centimetres.

Modern human brains are at least half as big again.

From the newsroom of the BBC World Service