Nature, biology, culture and the origins of technology in the Plio-Pleistocene.
At a minimum, some experts insist on differentiating Homo rudolfensis from Homo habilis, a distinction consistent with the impression that species diversity characterized hominid evolution throughout its history. Others explain substantial variations in terms of pronounced sexual dimorphism. Although the branching off of habilines must have involved mutations in the genetic structure of existing australopithecines, we cannot yet determine whether morphological alterations occurred in small increments or in dramatic spurts of 100,000 years or less. An abrupt species transition apparently did take place about 2.6 million years ago, and the brain size of habilines jumped appreciably around 600,000 years later. But beyond enlarged cranial capacity, which became roughly half that of modern humans by 1.8 million years ago, Homo habilis remained remarkably ape-like. Habilines were small, lightly built creatures, three or four feet in height, and sixty or seventy pounds in weight. Especially with their long arms, they resembled australopithecines from the neck down. When considered in strictly biological terms, they did not represent a momentous evolutionary advance.
As with their physical features, so with their behavioral attributes, habilines continued many earlier hominid patterns. Unprepared to handle cold weather, they may have reached the coastline of the Middle East in isolated bands, but most of the time they must have remained south of the Sahara, confining themselves to small, incessantly moving groups. They never established real home bases, but probably relied on safe cache sites to which they returned time and again. Plant foods constituted the bulk of their diet, although they seemed to have consumed meat on a regular basis. Less adept at climbing than australopithecines, they nonetheless scrambled into the treetops to pick fruit, to sleep, or to elude predators. They had an upright posture that seemed to indicate a virtual mastery of bipedalism. Given such continuities, what distinctive traits can we identify that would place habilines on a unique adaptive pathway? What characteristics now considered typical of our lineage indisputably set them apart from australopithecines?
Archeologists have found an answer in the earliest evidence for systematic tool manufacturing--a momentous accomplishment that gave birth to the development of culture as a primary adaptive mechanism for humankind. No later than 2.4 million years ago, East African hominids, who may have been the immediate precursors of Homo habilis, rather suddenly started to modify water-smoothed pebbles and rocks gathered in river beds, fashioning them into rudimentary stone artifacts suitably shaped to fit immediate needs. Soon after 1.9 million years ago, habilines had at their disposal an array of simple but clearly recognizable choppers, scrappers, burins, and hammerstones, all made in set patterns created by striking a core with a smaller stone to chip off a few sharp-edged flakes.
Known as the Oldowan industry, this basic technique for producing crude but advantageous devices eventually spread throughout much of Africa and Eurasia, continuing to be practiced in isolated areas as recently as 200,000 years ago. In the short run, however, the Oldowan tool kit certainly enhanced the habilines' chances of survival by allowing them to exploit savanna environments more efficiently. With the climates of East and South Africa becoming increasingly arid, they may have taken advantage of their stone tools to forage and hunt on amore regular basis in the expanding open woodlands and savannas, especially in places where greater meat consumption meant the difference between life and death.
Habilines could not have been the first creatures to rely on tools. To a limited extent, australopithecines surely used pieces of wood, bone splinters, and unmodified stones as spears, digging sticks, clubs, and pounding devices; and their recourse to tools must have involved activities a bit more varied and central to their lives than anything primatologists have found in the behavior of chimpanzees, the most sophisticated tool users among the other primates. Besides pushing twigs into termite nests to extract the edible insects, chimpanzees sometimes brandish clubs and throw objects to protect themselves. Such accomplishments, requiring only a modicum of foresight and problem-solving ability, bring immediate rewards and involve minimal modification of objects whose natural shapes suggest their possible functions.
As reasonably adept toolmakers, however, habilines must have been self-consciously aware of their actions. They had to possess an enlarged capacity to recall past experiences and anticipate future possibilities. With mental images of the desired objects already in mind, they needed to be able to collect stones of appropriate kinds and sizes, imagine how those stones would fracture when struck in particular ways, repeatedly produce devices with similar forms, and then purposely retain them for use at other times and places. In the development of the Oldowan tool industry, Homo habilis revealed a degree of creativity that no australopithecine or other primate could possibly have replicated.
The invention of stone tools nonetheless resulted in surprisingly few immediate behavioral changes. Around 2million years ago, habilines occasionally made bone artifacts and were starting to refine their woodworking skills. Several hundred thousand years later, they may have built the oldest windbreaks and crudely enclosed shelters. From scattered archeological evidence, we can reasonably suppose that soon thereafter they traded for artifacts manufactured as much as ten miles from their cache sites. Reasonably sharp, intentionally designed Oldowan tools helped them accomplish with greater efficiency such already familiar tasks as cutting, chopping, scraping, and digging, bringing about advantages which allowed them to broaden their subsistence strategies through increased dependence on meat. While the bulk of their diet still consisted of vegetable foods, habilines probably turned with growing frequency to opportunistic scavenging of predator kills and expert tracking of small game animals. Although their hunting activities remained limited and they may never have been able to prey upon large mammals, they were obviously defining the basic contours of the gathering and hunting adaptation in which our direct ancestors spent most of their history.
As habilines moved into a gathering and hunting context, the social organization of their small bands underwent commensurate alterations. Hunting even on a modest scale surely encouraged cooperation and food-sharing between individuals well beyond what we find among chimpanzees. Assuming that males always did much of the hunting, habilines probably established a clearer division of labor between the sexes, although males must have continued to help females in their vital food-gathering chores, especially when hunting prospects seemed unpromising, while the females participated in the butchering and transporting of scavenged meat. The evolutionary enlargement of the brain that coincided with the extension of hunting activities may have retarded the physical maturation of newborn habilines, further intensifying group interaction by prolonging the parental care invested in youngsters.
The demands placed on individuals by complicated social relationships may also have contributed to the development of the brain, which accelerated with Homo habilis after several million years of only modest change. Manual dexterity, bipedalism, and tool use simultaneously showed signs of improvement, all evolving together with enhanced mental capacity. By the time they were crafting Oldowan tools, habilines had brains roughly half the size of those possessed by modern humans. But size alone did not open up the cognitive gulf between habilines and other primates. What made the human brain truly distinctive was its division into two a symmetrically structured hemispheres, each containing identifiable areas designed to control particular mental and behavioral functions. Among other consequences now vital to our existence, this lopsided arrangement ultimately made about eighty percent of us right-handed, a tendency that became evident for the first time in the tool making abilities of Homo habilis. Stone artifacts associated with the Oldowan industry seem to have been produced by right-handed creatures, a likely symptom of significant modifications in the architecture of the cerebral cortex. Deliberately shaped stone tools were themselves indicative of unprecedented conceptual ability, for even the most primitive craftsman had to envisage the desired object lying within an unchipped pebble and devise manufacturing techniques appropriate for its production.
Like tool-making, articulate speech, often regarded as humankind's supreme innovation, was both an outgrowth of and stimulus for brain development. While paleoanthropologists have not been able to establish when our distant ancestors began to speak, we can safely assume that the evolution of a full capacity for language was a slow process. Virtually every animal can communicate in some fashion, but vocal signals, facial gestures, and body postures do not necessarily constitute a true language, which involves an understanding of signs as a system of symbols imparting to particular things and events a host of meanings far beyond what can be acquired through sensory awareness. Only human beings have a capacity for symbolic communication that truly carries them into the realm of abstract ideas and universal concepts. Habilines surely did not acquire a spoken language like those we know today. Yet they may have possessed a feature of the cerebral cortex known as Broca's area, a region connected with speech in modern humans. Despite their immature larynx, which would have limited the range of sounds they uttered, habilines may have articulated a combination of vowels and consonants adequate for the exchange of some genuinely complicated ideas.
Once habilines, showing signs of heightened self-awareness, possessed the crude beginnings of language and a few fabricated material objects in the form of Oldowan tools, they must have been better prepared for survival through adaptations to the environment based on cultural as well as biological factors. They presumably had sufficient mental capacity to support a modest but expanding constellation of shared ideas, values, beliefs, and behavioral norms that imparted greater predictability to group interactions, and that could be learned readily by succeeding generations. Compared to australopithecines, they were thus more dependent on information stored in the cells of their brains rather than the molecules of their genes. Without intending to do so, they had moved further away from purely instinctual behavior and introduced the possibility of cultural evolution into their lives.
When superimposed on an evolutionary timescale, the development of early hominids into habilines assumes the appearance of a breathtaking punctuation. In just 2million years or so, our kind had become proficient bipeds, accomplished toolmakers, and adept socializers. They must have been emotionally responsive, and already displayed an amazing propensity for symbolism. In retrospect, we know that irregular and unpredictable pathways lay between habilines and anatomically modern humans. But given how we view ourselves, we are understandably tempted to view the origins of the genus Homo, bringing with it the earliest manifestations of technology among other things, as a critical milestone in the formation of intelligent life on planet Earth. And for world historians, the accomplishments of Homo habilis dramatize the relevance of what we once called prehistory for an understanding not only of particular problems such as the beginnings of technological innovation, but also of the long and complicated processes by which our kind became fully human.
Ciochon, Russell L. and John G. Fleagle (eds.). The Human Evolution Source Book. Englewood Cliffs, New Jersey: Prentice Hall, 1993.
Gibson, Kathleen R. and Tim Ingold (eds.), Tools, Language and Cognition in Human Evolution. Cambridge and New York: Cambridge University Press, 1994.
Klein, Richard G. The Human Career: Human Biological and Cultural Origins .Chicago and London: The University of Chicago Press, 1989.
Lewin, Roger, Human Evolution. Fourth Edition; Malden, Mass.: Blackwell Science, Inc., 1999, Renfrew, Colin. The Explanation of Culture Change: Models in Prehistory. Pittsburgh: University of Pittsburgh Press,1973.
Southern Methodist University
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|Title Annotation:||FOCUS ISSUE and TEACHING FORUM|
|Publication:||World History Bulletin|
|Date:||Sep 22, 2008|
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