Searching for the emergence of stone tool making in eastern Africa

Abstract

Modern humans rely entirely on technology for their subsistence, and the interaction between technological and biological adaptations has played a key role in the evolution of our lineage. When exactly technology emerged in the fossil record and thus started to shape primate evolution has appealed to researchers since the beginnings of paleoanthropology as a discipline and, as Braun et al. (1) show in PNAS, is still today a source of important discoveries. Our closest relatives at present, the chimpanzees, have a rich material culture that varies geographically (2) and comprises the use of a wide variety of tools, including leaves, clubs, sticks, stones, and others. Although our ancestors most likely also used an array of organic materials, stones are usually the only artifacts preserved in the record and, therefore, are key to trace the emergence of technology in human evolution. For nearly a century, the Oldowan defined by Louis Leakey (3) at Olduvai Gorge in Tanzania has remained the most solid evidence of earliest stone tool making in our lineage. Originally thought to be around half a million years old, the age of the Oldowan has been pushed back steadily (4) since the 1960s, with the Gona sites in Ethiopia at 2.58million years ago (Ma) being, until Braun et al.’s (1) discovery, the oldest evidence of this technology (5). The new site of Bokol Dora 1 (BD 1) at the paleoanthropological area of LediGeraru, also in Ethiopia, is slightly older than Gona at 2.61 to 2.58 Ma (1) and contributes to establishing ∼2.6 Ma as a firm date for the earliest Oldowan. But the Oldowan might have not been the first archaeologically visible technology in the paleoanthropological record. In recent years, two discoveries— Dikika and Lomekwi—have sparked fresh debate about the potential existence of stone tool technologies further back in time, at ∼3.4 Ma. At Dikika, Ethiopia, some bones bear traces interpreted as cut marks (6), which would evidence that Pliocene hominins were using stone tools to process mammal carcasses. Although no stone tools have yet been reported in Dikika, the site of Lomekwi 3 (Kenya) has yielded several lithic artifacts that are attributed to 3.3-Ma sediments (7), thus complementing the indirect evidence of stone tool use proposed for Dikika. While the evidence >3 Ma is not exempt of controversy (see recent reviews in refs. 8 and 9), Braun et al. (1) compare the lithic assemblage of BD 1 with that of Lomekwi and conclude that differences are significant enough tomaintain a separation between the Lomekwian culture—the name given to the new discovery in Kenya (7)—and the Oldowan, for which BD 1 is now the earliest site. Acceptance of this scenario would imply reconsidering some long-standing paradigms in paleoanthropology. For instance, an influential view established coalescence among the emergence of the genus Homo, the earliest stone tools, and the climatic change toward aridification at 2.9 to 2.6 Ma (10). The earliest fossils of Homo have been recently discovered in the same area of Ledi-Geraru as the Oldowan site reported by Braun et al. (1) and, although such human remains are 200,000 y older (11) than BD 1, given the fragmentary character of the paleoanthropological record, they do not necessarily challenge the scenario associating climate change with speciation and cultural responses. Accepting the validity of archaeological evidence at ∼3.4 Ma, however, changes substantially the scenario and decouples such association, as no significant climate changes have been detected in that particular time span, and hominins in both the Dikika (Australopithecus afarensis) and Lomekwi (Kenyanthropus platyops) areas are less derived than early Homo. Another intriguing implication is the ∼0.7-Ma gulf between Lomekwi and BD 1. Basic lithic technologies such as the Lomekwian and the Oldowan may have been discovered and then disappeared and reinvented again in the course of human evolution (12)—in a fragmented sequence of cultural gains and losses that could potentially explain why no archaeological evidence is found between 3.3 and 2.6 Ma. In my view, however, a scenario of independent inventions, disappearance, and rediscovery of stone tool flaking does not fit well with the evidence available for the Oldowan record from2.6Maonward, because the tight chronological clustering among Ledi-Geraru (1), Gona (5), and all of