Evidence of Fire

Fire can occur naturally, as when lightning strikes ignite dry grasslands (still a frequent occurrence in sub-Saharan Africa), or it can be intentionally set and controlled by humans. Fire, more than any other cultural attribute, has been considered the hallmark of humanity. But Homo erectus seems to have had a relationship with fire that was unique—they were partially in control of its power, unlike any other animal species, but still in awe of it, unlike modern humans.

Dragon Bone Hill is one of the earliest sites documenting the use of fire by hominids. Davidson Black reported the first discovery of evidence of fire the same year that the first undisputed stone tools were found—1931,14 but Henri Breuil and Teilhard de Chardin were probably the first to make the original observations.15 Black adduced four lines of evidence in support of his argument that Homo erectus had used fire: carbon deposits, ash accumulations in hearths, burned bone, and fire-cracked stones (presumably used around campfires). All of these aspects of the evidence for fire at Longgushan have recently been reinvestigated by multidisciplinary teams. We look at each of the types of evidence in turn.

In the Lower Cave deposits, a blackened level of sediment was found by excavators. Black took some of the sediment to a chemist at Beijing University, who analyzed it and confirmed it to be carbon. This was an important result because a number of elements, including manganese and iron, can stain sediments and give them a black color. Black made the deduction that the carbon residue was derived from the charcoal left over from a hominid campfire.

A new study has proved Black wrong in his deduction about the carbon level. Paul Goldberg, a geologist at Boston University, and his colleagues reanalyzed the black sediment in the remaining western wall of the cave excavation.16 They determined that the sediment is indeed carbon, but interestingly it comes from a low stratum of the cave (Level 10) in which flowing and standing water were the main cause of sediment deposition— not a place where any early hominids would be building a fire. The carbon level was one of many finely laminated strata laid down by standing water. Further analysis showed that the carbon was organic residue of undecayed plant remains covered by water, and not the remains of charcoal at all.

Sediments in the excavation that had originally been identified by Teilhard and Pei as light-colored silts were reinterpreted as ashes after 1931 when it was determined that fire had been present at the site. Again, it is likely that Breuil's extensive experience in French Paleolithic cave excavations, in which he routinely found large accumulations of wood ash from early human hearths, influenced this reanalysis.

In 1998 geochemist Steve Weiner of the Weizmann Institute of Science and his colleagues took another look at these presumed ashes from Longgushan.17 For comparison they used their in-depth analyses of the undisputed Neandertal hearths at Hayonim Cave, Israel. They found that the Chinese sediments lacked the telltale phytoliths that are so common at Hayonim. Phytoliths are small bits of calcite in the tissues of many plants, which provide support for leaves and stems. When fires have been stoked with tons of wood over many years, there is a substantial residue of their phytoliths in the ashes. Weiner and his colleagues discovered that the light-colored sediments from Dragon Bone Hill contained no phytoliths. They therefore could not be ashes from wood fires fed by hominids. Further analysis showed that the sediments were in fact fine windblown sediments known as "loess" that had been reworked and deposited by water. The original identification of the sediments as "silt" by Teilhard and Pei had not been so off the mark after all. But, most significantly, it was obvious that the evidence for Homo erectus hearths had gone up in smoke.

The evidence for fire that has best withstood scrutiny has been burned bone. From an anthropological standpoint this evidence is doubly important because it establishes not only fire's presence in the cave but also clearly indicates its use. Lewis Binford and Nancy Stone noticed fire-cracked upper teeth of a horse in the Longgushan collections and deduced that Homo erectus had roasted horse heads. Other isolated bones of many species of large mammals showed evidence of having been burned while fresh, strongly implying cooking and eating by hominids.

A subset of burned bones from the site was colored blue, turquoise, or slate gray. Weiner and his colleagues undertook some experiments and discovered that only fossil bones heated to 600°C turned color like this (fresh bones either blackened or turned to ash). The conclusions from this line of evidence were that fires had burned at Zhoukoudian and that fossil bones had been exposed on the ground at the time. Rare fire-cracked stones, too large to have been washed into the cave, supported this evidence. Natural fire in a cave that still had a fair amount of standing water in it, even if there was a large accumulation of potentially combustible bird and bat guano, is much less likely in our opinion than the probability that hominids introduced fire into the cave. The geological context of burned bone, the evidence that some bone was burned while fresh—likely as incidental to roasting meat—and the presence of fire-cracked stones all argue that homi-nids used fire at Longgushan.

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