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Control of fire by early humans

The control of fire by early humans was a turning point in human cultural evolution that allowed for humans to proliferate due to the incorporation of cooked proteins and carbohydrates, expansion of human activity into the night hours, and protection from predators.

East Africa

The earliest evidence of human usage of fire comes from various archaeological sites in East Africa, such as Chesowanja near Lake Baringo, Koobi Fora, and Olorgesailie in Kenya. The evidence at Chesowanja consists of red clay sherds dated to be 1.42 Ma BP. Reheating on the sherds found at the site show that the clay must have been heated to 400°C to harden.

At Koobi Fora, sites FxJjzoE and FxJj50 show evidence of control of fire by Homo erectus at 1.5 Ma BP, with the reddening of sediment that can only come from heating at 200—400°C.

Olorgesailie, Kenya, has a site that has a hearth-like depression but no sign of charcoal. Some microscopic charcoal was found, but it is argued that it could have come from a natural brush fire.

In Gadeb, Ethiopia, fragments of welded tuff that appeared to have been burned were found in Locality 8E, but re-firing of the rocks may have occurred due to local volcanic activity. These have been found amongst H. erectus created Acheulean artifacts.

In the Middle Awash River Valley, cone-shaped depressions of reddish clay were found that could be created by temperatures of 200°C. These features are thought to be burned tree stumps such that they would have fire away from their habitation site. Burnt stones are also found in the Awash Valley, but volcanic welded tuff is also found in the area.

Southern Africa

The earliest definitive evidence of human control of fire was found at Swartkrans, South Africa. Several burnt bones were found among Acheulean tools, bone tools, and bones with hominid-inflicted cut marks. This site also shows some of the earliest evidence of carnivory in H. erectus. The Cave of Hearths in South Africa has burned deposits dated from 0.2 to 0.7 Ma BP, as do various other sites such as Montagu Cave (0.058 to 0.2 Ma BP) and at the Klasies River Mouth (0.12 to 0.13 Ma BP).

The strongest evidence comes from Kalambo Falls in Zambia where several artifacts related to the use of fire by humans had been recovered including charred logs, charcoal, reddened areas, carbonized grass stems and plants, and wooden implements which may have been hardened by fire. The site was dated through radiocarbon dating to be at 61,000 BP and 110,000 BP through amino acid racemization.

Near East

A more recently discovered site at Gesher Benot Ya'aqov, Israel, shows H. erectus or H. ergaster fires made between 790 and 690 ka BP.

Far East

In Xihoudu in Shanxi Province, there is evidence of burning by the black, gray, and grayish-green discoloration of mammalian bones. Another site in China is Yuanmou in Yunnan Province, where blackened mammal bones have been found.

At Trinil, Java, similar blackened bone and charcoal deposits have been found among H. erectus fossils.

Zhoukoudian

At Zhoukoudian in China, evidence of fire is as old as 500,000 to 1.5 million BP. Fire in Zhoukoudian is suggested by the presence of burned bones, burned chipped-stone artifacts, charcoal, ash, and hearths alongside H. erectus fossils in Layer 10 at Locality 1. This evidence comes from Locality 1 at Zhoukoudian where several bones were found to be uniformly black to grey. The extracts from the bones were determined to be characteristic of burned bone rather than manganese staining. These residues also showed IR spectra for oxides, and a bone that was turquoise was reproduced in the laboratory by heating some of the other bones found in Layer 10. At the site, the same effect may have been due to natural heating, as the effect was produced on white, yellow, and black bones. Layer 10 itself is described as ash with biologically produced silicon, aluminum, iron, and potassium, but wood ash remnants such as siliceous aggregates are missing. Among these are possible hearths "represented by finely laminated silt and clay interbedded with reddish-brown and yellow brown fragments of organic matter, locally mixed with limestone fragments and dark brown finely laminated silt, clay and organic matter." The site itself does not show that fires were made in Zhoukoudian, but the association of blackened bones with stone artifacts at least shows that humans did control fire at the time of the habitation of the Zhoukoudian cave.

Europe

Multiple sites in Europe have also shown evidence of use of fire by H. erectus. The oldest has been found in Vertesszollos, Hungary, where evidence of burned bones but no charcoal had been found. At Torralba and Ambrona, Spain, show charcoal and wood, Acheulean stone tools dated 0.3 to 0.5 Ma BP.

At St. Estève-Janson in France, there is evidence of five hearths and reddened earth in the Escale Cave. These hearths have been dated to 200 ka BP.

The mean evidence states that widespread control of fire began 125,000 BP.

Fire in the Americas

Although humans had been using fire for hundreds of thousands of years, an example of the powerful effects of the use of fire is the cumulative impact of burning by Native Americans. After arriving a few thousand years earlier, their use of fire profoundly altered the landscape of both continents. At about 4,000 years BP, the Archaic Indian cultures began practicing agriculture. Technology had advanced to the point that pottery was becoming common, and the small-scale felling of trees became feasible. Concurrently, the Archaic Indians began using fire in a widespread manner. Intentional burning of vegetation was taken up to mimic the effects of natural fires that tended to clear forest understories, thereby making travel easier and facilitating the growth of herbs and berry-producing plants that were important for both food and medicines. The result in many regions was "the conversion of forest to grassland, savanna, scrub, open woodland, and forest with grassy openings". As in many savannas in the world, the cerrado of South America have been coexisting with fire since ancient times; initially as natural fires caused by lightning or volcanic activity, and later caused by man. After the death of 90% of the native population around 500 years ago, grasslands, savanna, and woodlands succeeded to closed forest.

Changes to behavior

One of the primary changes to the behavior of humans due to the control of fire was the utilization of the light. With the light from fires, activity was no longer restricted to the day time. In addition, animals in general avoid fire and smoke. Another change that fire provided was the opening of the nutrition in cooked proteins.

Richard Wrangham of Harvard University argues that cooking of plant foods may have triggered brain expansion by allowing complex carbohydrates in starchy foods to become more digestible and in effect allow humans to absorb more calories.

Changes to diet

Stahl suggested that because of the indigestible components of plants such as raw cellulose and starch, certain parts of the plant such as stems, mature leaves, enlarged roots, and tubers would not have been part of the hominid diet prior to the advent of fire. Instead, the diet consisted of the parts of the plants that were made of simpler sugars and carbohydrates such as seeds, flowers, and fleshy fruits. The incorporation of toxins into the seeds and similar carbohydrate sources also affected the diet, as cyanogenic glycosides such as those found in linseed, cassava, and manioc are made non-toxic through cooking. The teeth of H. erectus and the wear on the teeth reflect the consumption of foods such as tough meats and crisp root vegetables.

The cooking of meat, as evident from burned and blackened mammal bones, makes the meats easier to eat and easier to attain the nutrition from proteins by making the meat itself easier to digest. The amount of energy needed to digest cooked meat is less than raw meat, and cooking gelatinizes collagen and other connective tissues as well as "opens up tightly woven carbohydrate molecules for easier absorption."