Refuting a Myth About Human Origins
Homo sapiens emerged once, not as modern-looking people first and as modern-behaving people later
A Better Way
Documenting and analyzing behavioral variability is a more theoretically sound approach to studying differences among prehistoric people than searching for the transition to behavioral modernity. Nearly everything humans do, we do in more than one identifiably different way. As Richard Potts of the Smithsonian Institution argued in Humanity’s Descent in 1996, our species’ capacity for wide behavioral variability appears to be uniquely derived. No other animal has as wide a behavioral repertoire as Homo sapiens does. And variability can be investigated empirically, quantitatively, and with fewer problems than occur in ranking prehistoric people in terms of their modernity.
One way to gauge early Homo sapiens’ behavioral variability is to compare their lithic technologies. Lithics, or stone tools, are nearly indestructible and are found everywhere hominins lived in Pleistocene times. Stone tools do not tell us everything we might wish to know about prehistoric human behavior, but they are no less subject to the selective pressures that create variation in other types of archaeological evidence. Lithic artifacts made by recent humans are more complex and variable than those associated with early hominins. Early Paleolithic stone tools are more complex and variable than those made by nonhuman primates. Thus, there is reason to expect that analysis of these tools will produce a valid signal about early Homo sapiens’ capacity for behavioral variability. Eastern Africa is an especially good place in which to compare early and later Homo sapiens’ stone technology because that region preserves our species’ longest continuous archaeological record. Restricting this comparison to eastern Africa minimizes the complicating effects of geographic constraints on stone-tool technology.
One of the most popular ways of describing variation among stone-tool industries is a framework that the British archaeologist Grahame Clark proposed in World Prehistory: A New Synthesis (1969). This framework describes lithic technological variability in terms of five modes of core technology. (In flintknapping, “cores” are the rocks from which flakes are struck, with the flakes later developed into various kinds of tools.) Variation in core technology is thought to reflect differences in ecological adaptations. Clark’s framework is a crude instrument, but it can be made into a reasonably sensitive register of technological variability if we simply note which of these modes are represented in each of a series of lithic assemblages. When it is applied to sites in eastern Africa dating 284,000 to 6,000 years ago, a more complex view of prehistoric life there emerges. One does not see a steady accumulation of novel core technologies since our species first appeared or anything like a “revolution.” Instead one sees a persistent pattern of wide technological variability.
What does this variability mean? Archaeologists’ understanding of lithic technology continues to grow, from experiments, from studies of recent stone-tool-using groups and from contextual clues in the archaeological record. Our understanding is far from perfect, but we do know enough to make some plausible interpretations. Pebble-core reduction (mode 1 in Clark’s framework), in which toolmakers strike flakes opportunistically from rounded pebbles or cobbles, is the simplest way to obtain a cutting edge from stone. Stone tools are still made this way in rural parts of eastern Africa. Its ubiquity in the archaeological assemblages probably reflects a stable strategy of coping expediently with unpredictable needs for cutting edges.
Large bifacial core tools (mode 2) are thought to have been dual-purpose tools. Their heft and long cutting edges make them effective in heavy-duty tasks, such as woodworking or the butchering of large animal carcasses. Thinner flakes knapped from bifacial core tools can be used for lighter-duty cutting or retouched into more functionally specialized forms. In recent archaeological contexts, large bifacial cutting tools are often correlated with people who moved their residences frequently, whereas expedient pebble cores are correlated with more lengthy occupations. High topographic relief and wide seasonal variation in rainfall make residential stability a difficult thing for even recent eastern African pastoralist groups to achieve. The persistence of this technology may reflect relatively high residential mobility among prehistoric eastern Africans.
The behavioral correlates of Levallois prepared-core technology (mode 3) are less clear, if only because the term encompasses so many different core-knapping strategies. Some archaeologists see Levallois prepared cores as reflecting knappers’ efforts to obtain desired tool shapes, or to produce relatively broad and thin flakes that efficiently recover cutting edge. These hypotheses are not mutually exclusive, and in the long run, each of them probably explains some part of why people made such cores in eastern Africa for a very long time.
Prismatic-blade core technology (mode 4) involves detaching long rectangular flakes one after another from a cone-shaped core. The most widely repeated hypothesis about the appeal of prismatic-blade production is that it produces greater amounts of cutting edge per unit mass of stone than other strategies. However, recent experiments by Metin Eren at Southern Methodist University and his colleagues have shown that this hypothesis is wrong. A far more likely appeal of this strategy is that the blades’ morphological consistency makes them easier to attach to a handle. Attaching a stone tool to a handle vastly increases leverage and mechanical efficiency, but it also restricts the range of tool movement and limits the portion of the tool that can be resharpened. The comings and goings of blade core technology in eastern Africa probably reflect a complex interplay of these strategic considerations.
Differing amounts of geometric microlithic technology (mode 5) are preserved in the most ancient and most recent assemblages in the east African sample. Geometric microliths are small tools made by segmenting blades or flakes and shaping them into triangles, rectangles, crescents and other geometric forms by blunting one or more of their edges. Too small to have been useful while hand-held, geometric microliths were almost certainly used as hafted tools. They are easy to attach to handles, making them suitable for use as projectile armatures, woodworking tools and aids to preparing plant foods. Archaeologists view microlithic stone-tool technology as a strategy for optimizing versatility and minimizing risk. Microlithic technologies first appear and proliferate among African and Eurasian human populations from about 50,000 years ago to around 10,000 years ago. This was a period of hypervariable climate, and it makes a certain amount of sense that humans at that time devised versatile and efficiently transportable stone tools. If, for example, climate change required people to frequently shift from hunting game to reaping grasses and back again, using microlith-barbed arrows and microlith-edged sickles would allow them to do this efficiently, without any major change to their technological strategies. Because microlithic tools are small, they preserve high ratios of cutting edge to mass. This means that if climate shifts required more seasonal migrations, individuals transporting microliths would be carrying the most cutting edge per unit mass of stone. Variability in the use of microlithic technology in eastern Africa probably reflects strategic responses to environmental unpredictability along with efforts to cope with increased subsistence risk by optimizing versatility in stone-tool technology.
How do the differences between earlier and later eastern African core technologies compare to variation among recent stone-tool-using humans? The range of variability in recent human stone-tool technology is greater than that in the eastern African sample. All five of Clark’s modes are to be found among the lithic technology of recent humans. Yet some technologies are not represented in the African sample. For example, more than 30,000 years ago in Australia, and later elsewhere, people began grinding and polishing the edges of stone tools. Such grinding and polishing reduces friction during work, making cutting tools more efficient to use and resharpen. In the New World, ancestral Native American flintknappers deployed a wide range of bifacial-core technologies fundamentally different from those seen in eastern Africa. They used these tools in contexts ranging from hunter-gatherer campsites on the Great Plains to Mesoamerican city-states like Teotihuacan. Differences in recent stone-tool technology reflect variability in adaptive strategies. No anthropologists in their right minds would attribute this variability to evolutionary differences among recent humans. If this kind of explanation makes so little sense in the present, what possible value can it have for explaining past behavioral variability among Homo sapiens?
The lithic evidence reviewed here challenges the hypothesis that there were significant behavioral differences between the earliest and more recent members of our species in eastern Africa. Obviously, there is more to human behavioral variability than what is reflected in stone tools. Using Clark’s technological modes to capture that variability, as described here, is just a first step. But it is a step forward. This emphasis on variability will gain strength if and when it is supported by more detailed analyses of the stone tools and by other archaeological evidence.