Evolving for survival - Homo habilis as the foundation for modern human life
By Whitney Nekoba
Swarthmore College '08
Spring 2007
The transition from Australopithecus to the genus Homo has undoubtedly been one of great discussion in speciation, chronology, and reason. The oldest recognized Homo species is H. habilis, discovered by Leakey, Tobias, and Napier in 1964, and lived 1.6 to 2.2 million years ago in the early Pleistocene era (Leakey, Tobias, & Napier, 1964). In Latin, habilis means skillful, and H. habilis excavations determined that the species demonstrated primitive tool use. However, tool use did not encourage this early Homo species’ migration out of Africa. Fossils have been unearthed only in localized regions along rivers and lakes in central and southern Africa (Susman & Stern, 1982). Although it was proposed that H. habilis also inhabited Asia, the data remains inconclusive (Wood, 1992). H. habilis survived and thrived in a savanna-like environment near water, with more seasonality than Australopithecus were accustomed to (Rice & Moloney, 2005; Akinade, 2002; Gorman, 1998). In this type of environment, was there pressure to change it for survival? Did these early humans have control over their environment? Was technology utilized to control this environment? H. habilis was a sedentary species; why was there no need to migrate? What implications does this have for modern humans today?
Classified under the genus Homo, H. habilis exhibited upright posture morphology and played a role in the gradual movement to terrestrial life. Evolutionary biologist Ernst Mayr suggested that the freedom of the “anterior extremity for new functions… stimulated brain evolution” (Wood, 1992, p. 787). Through phylogenetic analysis, H. habilis and H. rudolfensis are the intermediate species between A. africanus and H. erectus, the determined boundary between chimpanzee and human. Approximately eight character states of cranial, mandibular, and dental property were found in the parsimonious evolution from A. africanus to H. habilis. These character state changes include increased cranial vault thickness and height, and narrower tooth crowns with molar row reductions (Wood, 1992). H. habilis’ teeth size was relatively small and its brain size was considerably large for its body size (Ambrose, 2001). In addition, the wrist bones of the species suggest a thumb appendage strong enough to have powerful grasping abilities. This morphology, in addition to their newly evolved bipedal ability unique to the genus Homo, allowed H. habilis climbing capability similar to its ancestral state (Ambrose, 2001; Susman & Stern, 1982).
Although evolved from a common ancestor, Homo habilis began to perpetuate a more intellectual lifestyle for the Homo genus, thus separating itself from other primates. H. habilis is usually associated with the title of the first tool maker. Its enlarged cranial capacity as compared to earlier primates suggests that there was advancement in motor control of the hands and a potentiality for language development (Ambrose, 2001). Yet, the geographic distance between raw materials for stone tools were barely 10-20 kilometers apart, proposing that H. habilis enjoyed small home groupings (Ambrose, 2001). This may suggest that nomadic behavior of the species was minimal and that migration was unnecessary. The tools that resulted from the H. habilis era were mostly made of stone, and many of the tools were used in the manufacturing process of other tools (“Meet the relatives”, 2005; Gorman, 1998). Also, the complexity of the material use was far greater than that of chimpanzee tool-making suggesting an evolved, higher intelligence order (Gorman, 1998).
H. habilis were forced to evolve with the environment because of the decline in global temperature and humidity two million years ago. The climate change resulted in lesser tree density and a more savanna-like ecosystem in central and eastern Africa (Rice & Moloney, 2005). H. habilis had the selective advantage of being small and agile with powerful grasping abilities similar to their primate relatives. They were able to climb into trees to sleep and feed on plant matter and fruit (Susman & Stern, 1982). Yet these early humans, with different character states in comparison to their close chimpanzee relatives, exhibited features that benefited their survival over other primate species. With bipedal abilities, H. habilis did not rely as heavily on trees for protection from predators, a resource that was growing sparse with the changing environmental conditions. Primates, rather, still relied on close tree proximity in anti-predation measures. Climbing was an important skill of locomotive movement until hominids evolved into a permanent bipedal species (Susman & Stern, 1982). The behavioral plasticity of H. habilis to adapt to their environment provides insight to how climate and the changing environment put pressure on the genus to adapt and increase evolutionary fitness (Rice & Moloney, 2005).
With H. habilis’ larger brain size and its energetic cost, a nutritious diet was required (Gorman, 1998). Claims continue to argue the amount and ratio of meat to plant-source calories. Although many agree that the early human species scavenged for their food, Paleolithic archeologist Lewis Binford continues by suggesting that H. habilis was a “marginal scavenger” (Mithen, 1996). In order to capitalize on other predator’s kill, the species understanding and interpretations of predatory visual keys was extremely important. These early humans could predict the location of recent prey by use of tools, and were able to transport the meat to other locations for feasting (Gorman, 1998), suggesting increased knowledge and memory as compared to their primate predecessors. Dental research of H. habilis has provided insight on their consumption on non-meat foods. With the noted enamel and dentine erosion, it can be interpreted that this species regularly ingested acidic plant foods and ripe fruits (Puech, 1984). Meals of animal meat would not warrant the same erosion results. Apes eat ripe fruits as a large part of their diet and since H. habilis exhibited similar primate characteristics such as tree climbing, it would be obvious that fruits would remain a constant in diet (Puech, 1984). One other interesting addition to the dietary plans of early humans relates to the recent change of seasonality in the environment. When land-game resources ran low during drought or the early wet season, hunter-gatherers turned to the next efficient source of fat and nutrients. Fish was used as an adequate alternative to land-game, and have served as an excellent nutrient supplement (Stewart, 1994). The use of fish resources promotes the suggestion that early human habitation occurred along riverbeds and bodies of water, in addition to the development of useful technology to successfully catch enough fish and the learned acquaintance of frequented habitat (Stewart, 1994).
Group size of H. habilis was larger than Australopithecines, but small when compared to the proceeding species of Homo. The group size trend was positively correlated to the percent grooming time required by a species per day (Aiello & Dunbar, 1993). As grooming time increased, the amount of social interaction played a significant role in the development of vocal language and culture. However, Dr. Robin Dunbar, a British anthropologist and evolutionary biologist, suggests that H. habilis were just below the threshold for language development, although they had strong technical intelligence (Mithen, 1996). Larger social groups also were a type of life insurance and protection against predators and other human groups (Aiello & Dunbar, 1993). Yet, the advancement of technology or culture is entirely dependent on environmental, economic, and social bounds (Akinade, 2002), and H. habilis demonstrated the adoption of technology and culture within its environmental context easily.
With continued adaptation to the environment and development of tools and technology, there was a low force on H. habilis to migrate from their habitat. Reasons to move and immigrate would be due to an external pressure, including but not limited to: intolerable climate, unmanageable predation, inability to regenerate food sources, lack of shelter, and clashes of culture. As the climate changed from woodlands and rainforests to savanna-like terrain, early humans modified their lifestyle and generations continued to promote the Darwinian survival traits that increased the species’ fitness. In regards to predation, the species had primitive tool use and was probably able to defend themselves and their offspring to a healthy degree of survival. As a scavenging species, the individuals were knowledgeable enough about predation to determine their own safety. H. habilis was an omnivorous species and could feast on meat as well as plant and fruit matter. In addition, the fish population was an abundant food source and would not encourage nomadic movement by the peoples who utilized the resource (Stewart, 1994). The lack of shelter did not arise as an issue for the early humans because of their housing plasticity, where they could find shelter on the ground level or in trees due to their opposable, power-gripping thumbs, and their evolving bipedal nature (Susman & Stern, 1982). Finally, due to the lack of a omnipresent and powerful culture, there was no war that would warrant immigration by group disagreement. Without strong language skills, H. habilis in social groups did not have the same conflicts and problems that more modern species had, since the goal was more focused on the animalistic survival to the next day rather than the social and cultural happiness of the group for extended time.
It is essential to note that H. habilis and its descendants were able to exploit the environment in a healthy and successful manner, and were able to adapt to their ecosystem rather than destroying and rebuilding their environment to suit trivial individual or small group demands that is acknowledged and deemed socially acceptable today. Further studies would confirm or reject this idea through anthropological and archaeological research.
Literature Cited
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