The burning issue

The discovery and control of fire by our early human ancestors is considered a milestone in man's evolution. Not only was it a technological achievement that provided humans with a wider choice of food and an extended geographical range, it was also a sign of intelligence. Keeping a fire going showed that we could plan ahead, and its presence on dark nights must have provided a unique focus of social interaction - the caveman's equivalent of a modern dinner party.

The discovery and control of fire by our early human ancestors is considered a milestone in man's evolution. Not only was it a technological achievement that provided humans with a wider choice of food and an extended geographical range, it was also a sign of intelligence. Keeping a fire going showed that we could plan ahead, and its presence on dark nights must have provided a unique focus of social interaction - the caveman's equivalent of a modern dinner party.

Fire's importance cannot be overestimated. It provided heat and light and scared away dangerous predators at night. Fire also allowed humans to smoke and dry fish and meat, offering an early and invaluable form of food preservation. It also enabled them to experiment with a range of foods that could not be easily eaten raw or uncooked: the discovery of fire led to the invention of cooking.

Yet for all the importance attached to this critical point in human prehistory, there are wide disparities on the estimates of when exactly the first fire was kindled. Some studies suggest that fire might have been used as long as 1.4 million years ago. This suggestion comes from the discovery of lumps of baked clay found together with animal bones and stone tools at a stone age site at Chesowanja in Kenya. Naturally-sparked bush fire was initially dismissed as being able to cause such baking, but some scientists now believe that a burning tree stump that caught fire, or even volcanic heating, might be capable of creating the same effect.

More compelling evidence of the use of fire comes from research at the caves of Swartkrans in the Bloubank River Valley, in South Africa. Scientists have found more than 126 fossils from early hominids at this site, many of whom appear to have been killed by now-extinct predators such as sabre-toothed cats, which dragged the corpses into trees overhanging the cave complex.

Researchers working at Swartkrans have also discovered 279 fragments of burnt bones that have been dated to around one million years ago. Chemical and microscopic analyses indicate that the bones could have been subjected to temperatures consistent with having been burned in the hearth of a camp fire.

More recent studies of the bones, using a process called electron-spin resonance, has confirmed that they were heated to much higher temperatures than would be expected if they were simply caught up in a natural fire, says Anne Skinner of Williams College in Williamstown, Massachusetts.

Normally, a natural brush fire, sparked for instance by a lightning strike, would heat objects to a maximum temperature of about 300C. But these bones appear to have been heated to temperatures of 600C or more, which would only normally be seen in the hearth of a camp fire. The trouble is, no unequivocal evidence of a hearth has been found at Swartkrans.

The earliest and strongest evidence of the controlled use of fire using hearths dates to about 250,000 years ago, with the discovery of charred fragments of bone that must have been the result of being burnt at relatively high temperatures. Scientists have made these finds at several sites in Europe, such as Vertesszollos in Hungary and Menez-Dregan in northwest France. However, hearths do not become commonplace in the archaeological record until about 100,000 years ago.

More recent research, however, has pushed back the date at which fire was definitely controlled by more than half a million years. Archaeologists have found fragments of burnt flint and charred remnants from fruit trees at a site in Israel, where they believe humans had learned to control fire as early as 790,000 years ago, much earlier than previously accepted. The find is even more unusual in that it falls outside Africa, which is traditionally seen as the cradle of humanity, and the place were fire may have been first used.

The latest research comes from a group of paleontologists lead by Naama Goren-Inbar of the Institute of Archaeology at the Hebrew University of Jerusalem. His team has found charred fragments of flint, wood, fruit and grains at an excavation at Gesher Benot Ya'qov which lies on the shores of an ancient lake at the northern end of the Dead Sea. Extensive waterlogging of the site over tens of thousands of years has helped to preserve many of the fragments dug up from the site, some of which bear the unmistakable signs of being charred by fire.

Researchers discount natural fires, such as burning layers of peat, volcanic activity or brush fires, as responsible for these charred remains. "If surface wildfires were responsible for the burning of the organic and inorganic material we would expect to find high frequencies of burned items. However, less than two per cent of the excavated flint pieces and wood fragments are burned," they report.

They also found that the burnt fragments occurred at several layers in the excavations, showing that they must come from different periods. This suggests that once the ability to use fire was gained it must have been passed on to later generations. "We suggest that the hominids [early humans] who frequented the shores of the lake for over 100,000 years knew how to use fire and exercised that knowledge repeatedly throughout much of the Acheulian cultural period," the scientists said.

Some of the burnt fragments were found grouped together, suggesting that these early people used hearths. Six types of charred vegetation were found, including three edible species - olive, wild barley and wild grape. The obvious inference is that this was a hearth used for cooking.

Richard Klein, an expert on early humans, from Stanford University in California, says the Israeli scientists have made an important discovery. "I think they have made by far the best case yet for humanly controlled fire before 250,000 years ago."

Prof Goren-Inbar and his colleagues describe the location of the site as a "crossroads" between Africa, Europe and Asia. Altogether, they sifted through 23,454 seeds and fragments of fruit, and 50,582 lumps of wood, in their search for burnt specimens.

If humans were using fire in what is now northern Israel 790,000 years ago, it might explain the history of their early migrations to Europe - and how humans were able to colonise what was then a relatively cold region, says Paola Villa, from the University of Colorado. "The colonisation of Europe, where temperatures probably dropped below the freezing point at times, is generally tied to the use of fire," Dr Villa said.

Who lit these fires still remains a puzzle. Modern humans, or Homo sapiens, evolved in Africa less than 200,000 years ago, but older species, such as Homo erectus had already migrated across Asia at the time the Israeli fires were lit. Whoever was responsible, however, they showed remarkable intelligence and foresight. As Peter Gardenfors of Lund University points out in his book, How Homo Became Sapiens, keeping a fire alive was an insightful art. It required the realisation that fire consumed fuel, which led to the logical conclusion that new fuel needed to be added to keep the fire from going out, and an astute awareness that once the fire was out, its benefits would be lost, with possible disastrous consequences. Tending a fire also meant that these primitive human ancestors had to have a concept of the future. They must have realised that they had to collect firewood long before the fire went out. It was a true test of intelligent forward planning.