It has been suggested that Homo erectus was adapted primarily to eat cooked foods, since it lacked the heavy jaws of earlier hominids, particularly the Australopithecines. Evidence of fire is ubiquitous in archaeological sights younger than about 400 000 years old, i.e. sights used by Neanderthals and modern humans, but the situation at older sights is less clear. Traces of fire have been reported at sights up to 1.5 million years old, but none of these is clear cut, with signs of reworking and uncertain dating. The oldest sights from which the use of fire can be confidently claimed are between 700 000 and 800 000 years old in the Middle East.
In a paper published in the Proceedings of the National Academy of Sciences on 2 April 2012, Francesco Berna of the Department of Archaeology at Boston University announce the discovery of fire traces from a 1 million year old horizon in the Wonderwerk Cave in Northern Cape Province, South Africa.
Map showing the position of the Wonderwerk Cave. From Berna et al. (2012).
The Wonderwerk Cave is a phreatic tube (cave formed by pressurized water) through Precambrian dolostone (chemically altered limestone) in the Kuruman Hills of Northern Cape Province. It has been studied since the 1970s, and has a well understood stratigraphic sequence (chronology). It shows two stages of settlement an Oldovan stage (earliest stone age, generally between 2.6 and 1.7 million years ago, associated with Homo habilis) overlain by an Acheulean stage (a more advanced technology that appeared about 1.8 million years ago and which is associated with Homo erectus, and sometimes other members of the genus Homo).
Map of the Wonderwerk Cave. From Berna et al. (2012).
The fire remains were found on a horizon between two layers confidently dated to 1.27 and 0.98 million years old, and which is generally believed to be 1.07 million years old. The remains comprised fire altered plant and bone remains, and stone tools that had apparently been split from their parent rocks using fire.
The researchers were able to rule out reworking of the burned material at the site, and also spontaneous combustion of bat guano, which sometimes occurs in caves but which leaves distinct chemical signatures. They estimate from the extent to which bone samples were altered that the fires had reached temperatures of about 500°C, consistent with grass or leaf fires, but not the burning of wood. In addition they did not find remains of any wood (though this in itself is not proof of anything; absence of evidence is not evidence of absence).
Bone samples from Excavation 1 (see the map of the Wonderwerk Cave, above). (A) shows signs of heating to in excess of 400°C, (B) has either not been heated, or has been heated to less than 400°C.