The manufacture of patterned, chipped stone tools by early hominins appears to have led to the co-evolution of manual praxis, language, and expansion of the brain. Between approximately 2.6 million years ago (mya) and 200,000 years before present (yrs bp), the hominin brain nearly tripled in size, as indicated in the figure below.
Some Points on Lithics
Stone (lithic) tool manufacture requires strong, fast, highly controlled (precise) manual praxis (finely attuned awareness and function of the hands). Manipulation of particular types of stone cores (e.g., silicate-based materials with predictable conchoidal fracture) will create a variety of flaked or chipped tools (e.g., chopper, hand axe, scraper, knife, projectile point). The cores, flakes, and tools made by early hominins and modern humans have specific characteristics that distinguish them from features caused by natural processes (e.g., heat, frost, a fall). These features include a striking platform, bulb of percussion, and ripples, as illustrated in the diagram below.
Features of a chipped stone flake. Two views (A: fontal; B: profile) of a flake struck from a core illustrate key characteristics of a purposely made flake.
Worked stone cores are percussed with (typically) harder materials (e.g., other rocks, bone, antler, wood) using a sharp, forceful blow to break off flakes in succession, removing pieces of the core to form the desired tool or finished product. Flakes may also be removed with hard (e.g., harder igneous or metamorphic based rocks) or soft (e.g., antler, bone, hard wood) hammers in carefully controlled strikes. The basic methods are illustrated in the diagram below.
Two basic percussion techniques
The complex motor tasks associated with stone tool production have a strong spatial-cognitive component that activates the neocortex (cerebrum) and cerebellum, which are the areas of greatest brain expansion in hominin evolution. The sometimes tedious and frustrating job of creating stone tools requires motivation, self-control, and future planning: the ability to visualize the final product and its use. Understanding the characteristics of the stone being worked, and the physics of lithic fracture, is necessary. Nuances to successfully create a tool include:, the angle on a lithic edge, the orientation of the percussive blow, and precise aim and timing. Many stone tools are discarded unfinished due to mistakes in knapping. Coincidently, these discarded waste flakes often signal an archaeological site. All of this knowledge is difficult to learn through self-teaching or imitation alone.
Debate continues as to who were the first toolmakers. There is some evidence from East Africa of stone tools associated with Australopithecines ca. 3.3 mya. However, by at least 2.6 mya the Oldowan industry appears in Africa. Oldowan tools may be associated with Australopithecines and/or Homo habilis. The Oldowan industry is composed predominantly of cores, which are lumps of stone that have been slightly modified by removing small pieces around the edges, hammerstones (identified from battering on their surfaces), and flakes struck from the cores offering sharp cutting edges. Flakes are very sharp and useful for butchering animal carcasses. Core choppers were also used to crack open bones to extract nutrient-rich marrow. These crude, simple choppers, and cutting tools are simplistic in design, yet they allowed early hominins to exploit a new niche: animal resources and meat eating. The following figures present some Oldowan tools.
Oldowan choppers from Melka Kunture, Ethiopia. Ca. 1.7 mya.
Drawing of an Oldowan chopper.
By 1.6 mya, bifacially worked cutting tools appear in the fossil record in Africa, known as the Acheulean Industry. The Acheulean toolkit is composed primarily of the hand axe, a teardrop-shaped tool. It also includes assorted cleavers which are characterized by large flakes that were shaped by striking smaller flakes from around two opposing sides-bifaces-to create sharp edges. The Acheulean stone tool industry that Home erectus used displays an advance over the earlier Oldowan tools. These tools are made with a mental template and a preconceived idea in mind; they are not simplistic like the Oldowan tools. The figures below depict Acheulean hand-axes.
Image on left: Handaxe from Isampur, India, about 1.1 million years old. © Copyright Smithsonian Institution.
Image on right: Handaxe from Meyral, France, about 250,000 years old. © Copyright Smithsonian Institution.
Acheulean Handaxe. Dordogne Region, France. Courtesy of the Science Museum of Minnesota.
Some Aspects of the Brain
Stone tool production activates various areas of the brain, such as the cerebrum, cerebellum, and the frontal gyrus. One region in the frontal lobe, Broca’s area, is associated with speech, language, music, math and complex manual actions (manual praxis). Scanning techniques (e.g., Magnetic Resonance Imaging, Positron Emission Tomography) of modern subjects creating stone tools reveal the different areas of the brain are activated when making relatively simple Oldowan tools and more complex Acheulean tools. The figure below reveals one indicator of expanded brain power with more sophisticated toolmaking. In the illustration, numbers 1-4 denote regions active when making both Oldowan and Acheulean tools (i.e., dorsal intraparietal sulcus, anterior intraparietal sulcus, supramarginal gyrus of the inferior parietal lobe, ventral premotor complex). Numbers 1-6 indicate regions utilized when making Acheulean tools (i.e., dorsal intraparietal sulcus, anterior intraparietal sulcus, supramarginal gyrus of the inferior parietal lobe, ventral premotor complex AND dorsal premotor cortex, inferior frontal gyrus).
Some Notes on Language
In the 19th century, Charles Darwin suggested a connection between the intellectual challenges associated with tool manufacture and language as seen in the extreme encephalization of modern humans. However, when toolmaking was observed in nonhuman species (e.g., Jane Goodall’s report of chimpanzee tool use in the mid-20th century), toolmaking as a driver of evolution in humans fell out of favor. Recent research has brought new insights into how we have learned and taught each other to make tools - a process that may have enlarged our brains and spurred language. While imitation and practice are helpful, the nuances of strategy and tactics of stone tool manufacture are best learned from others, particularly via language. Increased manual praxis would allow for increased communication through gestures (associated with Broca’s area), facial sensorimotor systems, and perhaps vocalizations.
It is not yet known what form of language early hominins/Homo had, which may have ranged from gestures, vocalization, and signs, to exosonatic (symbolic) and mimetic (imitative) forms. By approximately 500,000 years ago, the Homo brain had increased synaptic malleability and connectivity. In addition to a big brain, the capacity for spoken language includes morphological changes to the supralaryngeal airway (with a relatively enlarged oral cavity) and the hyoid bone. The hyoid bone is U-shaped and rests under the chin, supporting the tongue, and has a unique shape in the genus Homo. An approximately 400,000 year old Homo erectus hyoid bone from Italy is markedly different from chimpanzee and Australopithecus afarensis hyoid bones, suggesting that Home erectus had the capacity for speech. Genetic research has focused on the FOXP2 gene, the so-called ‘gene for language’. A mutation in the gene occurring between 240,000-270,000 years ago in populations ancestral to living humans is implicated in motor control and cognition. This polymorphism allows for articulate language and enables the use of grammar. The figures below depict the position of the hyoid bone, its characteristics and a comparison with a chimpanzee hyoid bone.
Human hyoid bone
Human hyoid bone (left) and Chimpanzee hyoid bone (right)
The concurrent changes to the brain (increased connections and expansion) is a likely precursor to language (offering a significant learning advantage). Protolinguistic communication would be subject to selective pressure on the early hominin brain, producing adaptations that support language, along with physical adaptations to produce speech (i.e., the supralaryngeal airway, hyoid bone). Tools made by humans share a linguistic structure, as they are assembled in procedural ways (analogous to syntax) that have a nearly infinite capacity for variation (analogous to lexicon).
