Untangling human origins

Nowadays, it’s pretty easy to tell a person from an ape. Millions of years ago, the differences would have been much harder to pick out.

According to the scientific theory of evolution, apes and people have a common ancestor—one ancient animal from which both species evolved. At some time in the past, however, the creatures that would become humans started to differ from the creatures that would become apes and chimpanzees.

This computer reconstruction shows an ancient skull that its discoverers say is the earliest known human ancestor.

Michel Brunet, University of Poitiers/MPFT

A few years ago, anthropologists digging in the African country of Chad discovered some intriguing fossils. They found a skull, along with some teeth and jaw pieces, that was between 6 million and 7 million years old.

Because the face and teeth resembled those of later human ancestors, the scientists said that the fossils were those of a human-like, or hominid, species—even though the skull could hold only a chimp-sized brain. They called this creature Sahelanthropus tchadensis.

Not everyone agreed with this conclusion. Another group of anthropologists argued that the fossil pieces came from an ancient ape.

Now, the scientists who found the bones have dug up more fragments. And, because some of the original skull bits had been squished, the researchers used a computer program to unsquish the pieces and fit them together into a three-dimensional picture of the skull.

The newly found teeth look more human than chimp, the researchers say. Moreover, the computer image of the skull shows a human-like flat face.

The way the skull meets the spine and neck might also have allowed this primate to walk upright, they add. To confirm this, however, scientists would have to find leg bones as well.

The new information strengthens the view that the old bones belong to the earliest known human ancestor, the scientists conclude. This creature lived just after the split between the human and chimpanzee evolutionary families.

Here’s a model of what the head of the oldest known human ancestor might have looked like.

MPFT

Other anthropologists still aren’t convinced that this is our earliest ancestor. Humans and ancient apes looked a lot alike 7 million years ago, they say, and some features of the fossil skull are more ape-like than human-like.