The Brain

The human brain has gone through two major changes in size. One occurred two million years ago, when the Homo genus appeared. The second about 800,000 years ago. The changes originated in Africa and diffused with migration.

Leslie Aiello believed the first increase was related to a dietary change from plants to meat. Lucy and the Australopithecus genus were herbivores, Homo habilis were carnivores or omnivores.

Aiello argued meat was easier to digest, so less energy was required to maintain the body. The unused energy was transferred to the brain, with a consequent expansion of brain size and shrinkage of the gut. Her evidence included increased cranial size, inferred gut size reduction from the shape of the thoracic cage and pelvis, the sheen left on stone tools characteristic of contact with tissue, and cut marks on animal bones.

The change in diet set in motion reciprocating changes. With more energy, the brain was able to oversee improvements in technology and hunting. There weren’t changes in form so much as improved skills in hunting and manufacturing. When food became a problem, Homo habilis were able to transfer their skills to new materials and pioneer new locations. Environmental changes challenged their brains to increase mental facilities.

The second increase in brain size occurred at the onset of the first Pleistocene glacial period, the Pre-Pastorian. Soon after, C₄ pathway savannas began displacing woodlands and C₃ grasslands. Lightning ignited fires became more frequent.

Richard Wrangham has suggested the transition to cooked food was responsible for expanding brains. He posits hominins had learned to use fire. The problem has been finding evidence. Archaeologists began looking for reddened soils under rocks, rocks showing signs of having been heated to high temperatures, and traces of organic matter in soils or embedded in stones.

Two years ago, Francesco Berna’s team found ashes, carbonized leaves, and burned bits of bone in the sediments at Wonderwerk in South Africa. The fuel was something that produced a burning temperature between 750 degrees F (400 Celsius) and 1300 (700C) like grass, leaves or brush. They dated the strata to a million years ago. The cave then was inhabited by Homo erectus who used Acheulean tools manufactured from banded ironstone.

The first evidence for use of fire in Europe comes from a Homo erectus site in East Anglia, Beeches Pit, dated to the warm period between the Mindel and Riss glaciers 400,000 years ago. It contained reddened and shattered flints that had been heated to 400 degrees C. The amount of burned material suggests "fires were burnt through prolonged periods, perhaps continuously," by hominins who could use fires, but not ignite them.

A contemporary site at Hanover revealed a slightly more advanced species, Homo heidelbergensis, exploited both wood and heat. They left spears made from spruce and a throwing stick made from pine. There’s also a possibility they were heating resins from the inner bark of birch trees to make adhesives to affix points to spears.

Most of the bones were those of horses, Equus mosbachensis. Archaeologists also found a spruce stick with "carbonisation traces" that might have "functioned as a spit to roast or smoke pieces of meat."

Although the Heidelbergensis may have been using wood, Bibiche Berkholst said the presence of "Stephanorhinus hemitoechus and Bison priscus and the combined absence of the typical temperate forest species Sus scrofa and Capreolus capreolus may point to the disappearance of forests and the beginning of a period with a dominance of steppes." The first was an extinct species of rhinoceros. The others were steppe bison, wild boars, and red deer.

Notes: East Anglia is in England; Hanover is in Germany.

Aiello, Leslie C. and Peter Wheeler. "The Expensive-Tissue Hypothesis," Current Anthropology 36:199-221:1995.

Berkholst, Bibiche E. The Large Mammal Fauna of the Pleistocene Site Schöningen 13II: The Levels Schö 13II-1, 13II-2 and 13II-3, 2011.

Berna, Francesco, et alia. "Microstratigraphic Evidence of in situ Fire in the Acheulean Strata of Wonderwerk Cave, Northern Cape Province, South Africa," National Academy of Sciences, Proceedings 109:E1215-E1220:2012.

Gowlett, John A. J. "The Early Settlement of Northern Europe: Fire History in the Context of Climate Change and the Social Brain," Comptes Rendus Palevol 5:299-310:2006.

Roebroeks, Wil and Paola Villa. "On the Earliest Evidence for Habitual Use of Fire in Europe, National Academy of Sciences, Proceedings, 108:5209-5214:2011.

Villa, Paola. Quoted on use of possibility of heated birch bark, University of Colorado Bolder press release for 14 March 2011, "Neanderthals Were Nifty at Controlling Fire, According to Cu-Boulder Researcher. Nothing has been reported since.

Wrangham, Richard W., et alia. "The Raw and the Stolen: Cooking and the Ecology of Human Origins," Current Anthropology 40:567-594:1999.