Since humans and chimps took different evolutionary paths, around 5 to 8 million years ago, the human skull has gradually changed shape. The jaw and teeth have become smaller while the brain cavity has grown larger. See the transitions in the different hominid species below.
Chimpanzees are the closest living relatives of modern humans. We are thought to have diverged from their line around 5 to 8 million years ago. The brain cavity of a chimpanzee's skull is much smaller than a human's. Its teeth are larger and its face is more protruding.
Australopithecus afarensis evolved in Africa over 3 million years ago and it is thought to have been the first species to walk upright. The size of the brain cavity is closer to that of a chimp than a modern human - it's much smaller than the brain cavity of more recent hominid species. The shape of the face is also similar to that of a chimp. However, the teeth are smaller and more human-like.
Homo erectus evolved in Africa around 2 million years ago and gradually spread across Asia. It has a greater brain capacity than Australopithecus afarensis but its brain is still much smaller than that of neanderthals and modern humans. It also has a heavier brow ridge, and the face is more protruding.
Homo floresiensis was only 1m tall and there is still some debate about whether it is a separate species, a diseased modern human, or a dwarfed Homo erectus. Its brain cavity is smaller than any of the other hominid species, and also smaller than a chimp's.
Neanderthals evolved around the same time as modern humans and died out around 25,000 years ago. Like modern humans, they have a large brain cavity.
Homo sapiens evolved in Africa around 100,000 years ago. They have a larger brain for their size than any other hominid species. Their relatively small and they have the unique feature of a chin.