Ancient human ancestors got all fired up.

Ancient human ancestors got all fired up

The earliest direct evidence of fire use, in the form of charred animal bones dating to between 1 million and 1.5 million years ago, has been uncovered in a South African cave, report two anthropologists in the Dec. 1 NATURE.

The cave also contains animal bones with cut marks suggesting butchery, but whether early hominids -- members of the evolutionary family that includes modern humans -- used fire for cooking, protection from predators or warmth remains unclear, say C.K. Brain of the Transvaal Museum in Pretoria and Andrew Sillen of the University of Cape Town, both in South Africa.

"We now know that fire was repeatedly used at Swartkrans by early hominids," Brain told SCIENCE NEWS. Since previous excavations in the cave complex unearthed the remains of hominids killed by large cats, such as the saber-toothed tiger, he suggests the initial purpose of building fires was to keep these predators away at night.

The Swartkrans evidence appears more conclusive than a 1981 report of fire use by hominids at a 1.4-million-year-old site in Kenya. Archaeologist John A.J. Gowlett of the University of Liverpool, England, and his co-workers found magnetic changes in pieces of charred clay probably caused by a fire. This charring, however, might have resulted from a natural brushfire, not an ancient campfire.

Prior to the South African discovery, the earliest direct evidence for the controlled use of fire occurred at a Chinese site dating back nearly 500,000 years.

From more than 59,000 fossil fragments unearthed at Swartkrans, Brain and Sillen identified 270 burnt pieces. The fragments came from numerous layers of one level of the cave that is at least 1 million years old, but not from two older levels dating to about 1.8 million years ago.

Researchers compared chemical and microscopic analyses of the fossils to data from the leg bone of a modern South African hartebeest burned in a campfire. The fire was made with branches of white stinkwood, a tree common around Swartkrans. Bits of stinkwood are in the fossil deposits.

The anthropologists say the fossil bones burned at temperatures between 200[deg.]C and 800[deg.]C, an estimate consistent with temperatures of experimental campfires made from white stinkwood.

"This is very convincing evidence for fire use by early hominids," says anatomist Pat Shipman of Johns Hopkins University School of Medicine in Baltimore, who has seen the Swartkrans remains. "If the control of fire goes back somewhere between 1 million and 1.5 million years, it would have opened up the night to a new spectrum of activities."

Only the remains of Australopithecus robustus, which belonged to a small-brained line of hominids that became extinct around 1 million years ago, have been found in the Swartkrans level containing the burnt bones. But Shipman and Brain, as well as Gowlett, say Homo erectus most likely made the fires in the cave. The larger-brained H. erectus, a direct ancestor of modern humans, lived from about 1.6 million to 300,000 years ago and its remains appear in other Swartkrans deposits.

"Given the evidence, we need to rethink a lot of things about early hominids," Shipman says.

For instance, the Swartkrans campfires date considerably before H. erectus finds outside of Africa, thus throwing doubt on the theory that the taming of fire was a key factor in the northward migration of H. erectus.

In addition, Shipman notes, hominids could have warded off nighttime predators from animal carcasses with the help of campfires. Previous estimates of meat eating among early hominids may be conservative, she says.

Although two of the burnt bones at Swartkrans are finger bones of A. robustus, they were probably part of debris left on the cave floor, Brain says. "It's tempting to think robustus was included in cooking, but evidence [for that conclusion] is slim."