Ann Gibbons was at the AAPA meetings early last month, and she reports in the current Science on some of the research. Her article about the use of early Oldowan tools from Kanjera, Kenya focuses on the evidence for plant processing:
To find out just what early Homo was doing with the tools, [archaeologist Thomas] Plummer enlisted archaeologist Cristina Lemorini of the University of Rome, "La Sapienza." She studied replicas of the Kanjera tools, made with the same kinds of stone, that modern Hadza hunter-gatherers of Tanzania had used to butcher animals, process wild tubers, cut grass, and work wood. Then, using confocal and metallographic microscopes, she compared patterns of wear on the edges of the Kanjera tools with those on the replicas. She reported that the ancient tools had telltale signs of being used to process plant materials, such as cutting grass, and the distinct striations made by sediment as tools were used to clean and section fibrous tubers. She also saw patterns consistent with defleshing carcasses and woodworking, possibly to make wooden tools.
Kanjera has been the subject of some very interesting raw material analyses over the last couple of years, by David Braun and colleagues (2008, 2009), documenting the selectivity of the Oldowan-makers for particular kinds of raw materials -- studies that have counterparts at other early Oldowan sites, including Lokalalei (Harmand 2009).
Meanwhile, the analysis of use-wear and plant residues on stone tools has advanced markedly in the last ten years. Use-wear analysis considers the kind of microwear produced on artifacts by repeated use against materials like wood, hide, meat, and bone. For many years, archaeologists have worked on microwear -- for example, Lawrence Keeley and Nick Toth (1981) showed that wear patterns on the edges of Oldowan tools from Koobi Fora are consistent with use in both meat and plant processing. But use-wear analysis has undergone recurrent debate over the years, as people questioned the qualitative assessments of similarity between reference tools -- used by experimenters on known materials -- and archaeological artifacts. A short review of this history is given by Evans and Donahue (2008).
A certain ambiguity about use-wear studies remains unresolved -- how much of the results are in the eye of the analyst? It helps a lot to have additional evidence. Plant residues and phytoliths have increasingly provided such evidence -- the actual parts of plants adhering to stone tools with use-wear that looks like plant materials makes it look pretty likely that the tools were used on the plants. To list some highlights, we have:
Nuts and nutcracking at Gesher Benot Ya`aqov (Goren-Inbar et al. 2002).
Woodworking, as documented by phytoliths and plant fibers adhering to initial Acheulean tools from Peninj (Dominguez-Rodrigo et al. 2001).
Starch grains also can adhere to stone tools, and starch processing is clear in the Middle Stone Age of Mozambique (Mercader et al. 2008).
A range of starchy and woody plant materials were processed by Mousterian (presumably Neandertal) people from Starosele and later Upper Paleolithic people from Buran Kaya III -- similar between the two sites despite their difference in time (Hardy et al. 2001). Some tools had both mammalian hair and feather barbules attached.
There's an endless range of such studies; a deep literature, so that a few highlights don't really do it justice. A few studies, like the last one here, actually consider enough artifacts to start to develop an idea of the activity patterns of people. When you're only studying three or four artifacts that preserve any microwear, you've got evidence that a few things did happen sometimes, but you really don't have a full pattern.
Braun DR, Plummer T, Ditchfield P, Ferraro JV, Maina D, Bishop LC, Potts R. 2008. Oldowan behavior and raw material transport: perspectives from the Kanjera Formation. J Archaeol Sci 35:2329-2345. doi:10.1016/j.jas.2008.03.004
Dominguez-Rodrigo M, Serrallonga J, Juan-Tresserras J, Alcala L, Luque L. 2001. Woodworking activities by early humans: a plant residue analysis on Acheulian stone tools from Peninj (Tanzania). J Hum Evol 40:289-299. doi:10.1006/jhev.2000.0466
Evans AA, Donahue RE. 2008. Laser scanning confocal microscopy: a potential technique for the study of lithic microwear. J Archaeol Sci 35:2223-2230. doi:10.1016/j.jas.2008.02.006
Gibbons A. 2009. Of tools and tubers. Science 324:588-589. doi:10.1126/science.324_588b
Goren-Inbar N, Sharon G, Melamed Y, Kislev M. 2002. Nuts, nut cracking, and pitted stones at Gesher Benot Ya`aqov, Israel. Proc Nat Acad Sci USA 99:2455-2460. doi:10.1073/pnas.032570499
Hardy BL, Kay M, Marks AE, Monigal K. 2001. Stone tool function at the paleolithic sites of Starosele and Buran Kaya III, Crimea: Behavioral implications. Proc Nat Acad Sci USA 98:10972-10977. doi:10.1073/pnas.191384498
Harmand S. 2009. Variability in Raw Material Selectivity at the Late Pliocene sites of Lokalalei, West Turkana, Kenya. Pp. 85-97 in Hovers E, Braun DR, Interdisciplinary Approaches to the Oldowan. Springer, Amsterdam. Amazon
Keeley LH, Toth N, 1981. Microwear polishes on early stone tools from Koobi-Fora, Kenya. Nature 293:464-465.
Mercader J, Bennett T, Raja M. 2008. Middle Stone Age starch acquisition in the Niassa Rift, Mozambique. Quatern Res 70:283-300. doi:10.1016/j.yqres.2008.04.010