Hafted Tools

Diets changed during the early Pleistocene even before fire was used for cooking. Glaciers that sequestered water in ice fields affected rainfall levels everywhere on the planet. The drier climate altered vegetation, which in turn encouraged some animal species at the expense of others. Speciation wasn’t limited to the Homo genus.

Acacias spread through Gondwana before Australia began splitting from Africa some 184 million years ago. When legumes began diversifying in the Miocene, acacias also multiplied. The species used for gum arabic, Senegalia senegal, spread from East Africa into Arabia and west toward the Atlantic when savannas replaced rainforests.

During the Pleistocene, Davie Odee’s team said the "contraction and expansion of the Sahara desert in Central and West Africa, and interaction of climate with the Great Rift Valley and the elevated topographies of East and Southern Africa produced wide altitudinal ranges forming a complex mosaic of landscapes and localised climate regimes that functioned as refugia during extreme climate conditions." The drought resistant acacia adapted to lowlands and highlands, "forests, woodlands and savannahs."

Today, acacia seeds are dried for later consumption. In the nineteenth century, William Rhind heard Moors lived "almost entirely" on gum arabic when they were harvesting it in Sénégal and that "six ounces are sufficient for the support of a man during twenty-four hours." Anders Sparrman said, in southern Africa in the 1750s, "the Bushmen live on it for days together" when nothing else was available.

Herbivores browse the pods, leaves, and twigs. In Tanzania, modern elephants and giraffes prefer this species to all others. Leaves and twigs are about 15% crude protein, the green pods about 20%. Middle Stone Age nutrition could have improved when animals found plants with higher food values that then were stored in the blood, bone and muscle that later was consumed by hunters.

Margaret Schoeninger suggested body shape could have changed even when the percentages of animal and vegetables in the diet remained constant. One cause, as mentioned in the last post, would have been cooking. More interesting, she suggested technical modifications that made hunting physically less strenuous could have modified muscle development, which in turn would have effected skeleton formation.

One important innovation was adding handles to tools like the Homo heidelbergensis spears found in Saxony. Composite weapons first appeared at Twin Falls, another heidelbergensis site in the Zambian highlands between the Rift Valley and the Congo basin about 300,000 years ago. They were representative of the Lupemban technology found in Kenya, Zambia, and Tanzania.

Fifty thousand years before Mount Kenya had been glaciated and Kilimanjaro was probably still ice covered. The area would have dried during the cold years. Plant and animal migrations towards the wetter Congo basin may have begun. Hunters who followed might have confronted brush strewn landscapes that weren’t maintained by fires as often.

John Desmond Clark found a number of heavy duty tools at Twin Falls he believed were used for wood working. When Lawrence Barham reexcavated the site twenty some years later he found bone fragments, backed blades suitable for handles, and ochre of various colors.

The backed blades were probably attached to wooden handles with a mastic made from acacia sap. When the tree’s bark is broken, the sap forms globules on the surface. The greater the injury, the more sap. The tears eventually harden.

Unprocessed acacia mastic is not as strong as sap that’s been mixed with quartz or ochre dust. Andrew Zipkin’s team found it didn’t matter which was used. While Barham found ochre at Twin Falls, he didn’t mention finding traces on the backs of blades. It may have disappeared with time or hunters may not yet have recognized its utility.

Lyn Wadley thought joint failure might not have been a problem. She wrote, a "brittle, unloaded adhesive allows a projectile head to disengage its haft and implant itself in an animal; robust adhesive keeps a spearhead safely in its shaft."

If ochre were the reason pieces of colored clay were taken to Twin Falls, Wadley may have unintentionally replicated another part of the invention process when she tried to make mastic from the acacia species available near the Rose Cottage site in South Africa. She said when she was grinding ochre with sandstone, the process reddened "everything in a meterwide radius of the activity. Hands, arms, clothing, work surface, and anything lying nearby become covered in fine, red dust."

Individuals may have noticed their mastic covered hands were less irritated. Acacia sap has been used to treat inflamed skin, including burns. The ochre would have been more noticeable than its carrier. Attributing the healing affects to it would have been a reasonable supposition.

Ochre is a general term for many forms of iron oxides embedded in clay, of which red hematite is the best known. The reasons it was used are speculation: some claim it had symbolic value, some that it was utilitarian, some that its use on weapons was a form of hunting magic. The reason so many types were found at Twin Falls may simply have been the consequence of skilled tool makers experimenting to solve a problem.

Notes: Acacias are a large group of species within the legume family. In 2005 they were divided into four genuses. Before that time the one I’m discussing, Senegalia senegal, was known as Acacia senegal. The acacia used by Wadley was Vachellia/Acacia karroo.

The acid soils in east Africa destroy bones and other organic matter. Twin Falls was dated with uranium-thorium tests. It shares the Lupemban technology with Broken Hill in Zambia where remains of Homo rhodesiensis were found. Palaeontologists now believe rhodesiensis and heidelbergensis were the same.

Allen, O. N. and Ethel K. The Leguminosae, 1981.

Barham, Lawrence. "Backed Tools in Middle Pleistocene Central Africa and Their Evolutionary Significance," Journal of Human Evolution 43:585-603:2002.

Clark, John Desmond. Work discussed by Barham.

Duke, James A. "Acacia senegal (L.) Willd.," Handbook of Energy Crops, 1983.

Odee, D. W., A Telford, J. Wilson, A. Gaye and S. Cavers. "Plio-Pleistocene History and Phylogeography of Acacia senegal in Dry Woodlands and Savannahs of Sub-Saharan Tropical Africa: Evidence of Early Colonisation and Recent Range Expansion," Heredity 109:372-382:2012.

Rhind, William. The History of the Vegetable Kingdom, 1855; he doesn’t give his sources, but was working in Edinburgh.

Ruess, R. W. and F. L. Halter. "The Impact of Large Herbivores on the Seronera Woodlands, Serengeti National Park, Tanzania," African Journal of Ecology 28:259-275:1990.

Schoeninger, Margaret J. "Diet and the Evolution of Modern Human Form In the Middle East," American Journal of Physical Anthropology 58:37-52:1982.

Shanahan, Timothy M. and Marek Zreda. "Chronology of Quaternary Glaciations in East Africa," Earth and Planetary Science Letters 177:23-42:2000.

Sparrman, Anders. A Voyage to the Cape of Good Hope, Towards the Antarctic Polar Circle, and round the World: but Chiefly into the Country of the Hottentots and Caffres, from the year 1772 to 1776, 1789; quoted by Rhind.

Wadley, Lyn. "Putting Ochre to the Test: Replication Studies of Adhesives that May Have Been Used for Hafting Tools in the Middle Stone Age," Journal of Human Evolution 49:587-601:2005.

Zipkin A.M., M. Wagner, K. McGrath, A. S. Brooks, and P. W. Lucas. "An Experimental Study of Hafting Adhesives and the Implications for Compound Tool Technology," PLoS One, 10 November 2014.