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Chapter 12- From Hominin to Homo.doc

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Ben Evans

1 Chapter 13: From Hominin to Homo Bernard Ho - about 1.8 ma, a new creature called Homo ergaster appeared o very similar to humans in that these developed slowly, and infants must have been helpless at birth o large, robust bodies with long legs and short arms  committed to life on ground o probably learned to master fire and to hunt large game o have smaller brains that humans do, and their subsistence technology seems to have been much less flexible than ours Hominins of the Lower Pleistocene: Homo ergaster - Pleistocene epoch began 1.8 mya and saw a cooling of world’s climate o divided Pleistocene into three parts: Lower, Middle, and Upper  lower • 1.8 mya • sharp cooling of world’s climate  middle • sharply increased fluctuations in temperature and first appearance of immense continental glaciers that covered northern Europe 900 kya  upper • ended about 12 kya when a warm, interglacial phase of world climate began - Homo ergaster appears in African fossil record about 1.8 mya and disappears 0.6 mya o fossils found in Ethiopia, Tanzania, Kenya, and South Africa o most paleontologists assigned these African fossils to the species Homo erectus, but a growing number of paleontologists have come to believe that African specimens have become too distinct o new name given was Homo ergaster or “work man” - Homo ergaster appeared in Eurasia about the same time it was first known from Africa o Homo ergaster was the first hominin to make its way out of Africa  know this because there was a discovery of a lower jaw and Oldowan tools in sediments dated to 1.1 or 1.8 mya in Georgian (at archeological site Dmnaisi)  also uncovered two nearly complete crania at Dmnaisi that are very similar to African specimens of H. ergaster and dated around 1.7 mya  H. ergaster migrated out of Africa to Eurasia about 1.7 mya, taking their tools with them Morphology - skulls of H. ergaster differ from those of both earlier hominins and modern humans o retain many of characteristics of earlier hominins (marked narrowing behind eyes, receding forehead, no chin) o also show many derived traits, some of which are shared by modern humans  smaller , less prognathic face, a higher skull, and smaller jaws and teeth o also has some derived traits not shared by humans  horizontal ridge at back of skull (occipital torus)  large brow ridges o derived traits are probably related to diet 1 2  better adapted for tearing and biting with canines and incisors  less suited for heavy chewing with molars  teeth are smaller than australopithecines and paranthropines, but molars are reduced relatively more in comparison with incisors o has substantially larger brain than earlier hominins  average brain volume was about 800 cc (larger than brains of earlier apelike hominins- 500-700 cc) o larger body than earlier hominins - Postcranial skeleton of H. ergaster is much more similar to skeleton of modern humans that to that of earlier hominins, but it still differs from ours in interesting ways o found skeleton where fossils of Australopithecus anamensis, Paranthropus aethiopicus, and Kenyanthropus platyops were also found  skeleton of the H. ergaster was named KNM-WT 15000 o KNM-WT 15000 had same body proportions as people who live in tropical savannas today: long legs, narrow hips, and narrow shoulders  also had short arms, compared with earlier hominins  quite tall and also robust and heavily muscled  infants probably matured slowly and were dependent on their mothers for a long period of time • mother’s birth canal was same as it is in modern humans  sexual dimorphism was reduced • males were about 20% to 30% larger than females, making them less dimorphic than apelike hominins and only slightly more dimorphic than modern humans  may not have had spoken language • vertebral canal in thoracic region of back is larger in modern humans than in apes, and it contains proportionally thicker spinal cord • studies show that extra nerves that enlarge spinal cord innervate muscles of rib cage and diaphragm o the KNM-WT 15000 probably had less precise control over muscle of his rib cage and diaphragm  was first hominin that could run for long distances • may be useful in long-distance scavenging and hunting in open country - H. ergaster may have developed more rapidly than modern humans o researchers estimate that H. ergaster developed more slowly than australopithecines but still faster than modern humans  if this is true, that means H. ergaster did not have same long childhood period as humans  suggests that learning was not important in lives of creatures  still uncertain whether this is true Tools and Subsistence - H. ergaster made fancier tools than earlier hominins had made o associated with Oldowan tools o around 1.6 to 1.4 mya in Africa, H. ergaster added a new kind of stone tool called a biface 2 3 biface o most common type of biface is called a hand ax (shaped like a teardrop and has a sharp point at narrow end) o cleaver: lozenge-shaped biface with a flat, sharp edge on one end o pick: thicker, more triangular biface o bifaces are classified as Mode 2 technology  call the Mode 2 industries of Africa and western Eurasia (Europe and Middle East) Acheulean industry  suggests that toolmakers had a specific design in mind  Mode 1 tools of Oldowan industry had a haphazard appearance; no two are alike o hand axes have regular proportions: ratio of height to width to thickness  Implies makers had shared an idea for design - Hand axes were probably used to butcher large animals - hand axes were designed for: 1. butchering large animals 2. digging up tubers, burrowing animals, water 3. stripping bark from trees to get at nutritious cambium layer underneath 4. hurling at prey animals 5. dispensing flake tools - from experiments, Schick and Toth conclude that hand axes are best suited for butchery o sharp end of ax easily cuts through meat and separates joints o rounded end provides a secure handle - the Acheulean industry remained remarkably unchanged for almost 1 million years o Relatively little change over space and time in Acheulean tool kit from its first appearance about 1.6 mya until it was replaced 300 kya o Most assume that knowledge necessary to make a proper hand axe was passed from one generation to the next by teaching and imitation - Homo ergaster clearly ate meat, but there is controversy about whether they hunted or scavenged kills o One of the most compelling pieces of evidence that these hominins ate meat comes from skeleton of an H. ergaster woman  Her long bones are covered with a thick layer of abnormal bone tissue  This bone growth is symptomatic of vitamin A poisoning  Most likely way she got this would be to eat liver of a large predator o Several lines of evidence also suggest that H ergaster relied on meat  Hand axes seem to be well suited to butchery of large animals  Teeth of H. ergaster are well suited for biting and tearing and less suited for chewing tough plant foods 3 4 - Homo ergaster may have controlled fire o Archaeologists found baked earth beside stone tools at a site dated to about 1.6 mya o Experiment showed that soil under campfires reaches much higher temperatures than soil under grass fires or soil under smoldering tree stumps o Higher temperature produces a bowl-shaped layer of highly oxidized soil formed directly under the fire o Also, soil under fire becomes highly magnetized compared with surrounding soil o Researchers examined fire sites at Koobi Fora (site of H. ergaster) and found similar characteristics o Excavations in a cave at South Africa provide more evidence  Found burned bones - Homo ergaster is classified in genus Homo because it shares the same adaptive grade as later members of the genus o Data suggests that H. ergaster represented a marked departure from its predecessors Hominins of the Early Middle Pleistocene (900 to 300 kya) - World’s climate became colder and much more variable during Middle Pleistocene - During glacial periods, the world was dry and Africa and Eurasia were isolated from each other by a massive desert o During interglacial periods, the world was much wetter and animals moved from Africa to Eurasia o Temperature fluctuations had massive effects on world’s biological habitats o Also had effects on dispersal of animal species, including hominins in the Middle and Upper Pleistocene  During glacial periods, deserts spread across northern part of Africa, making this region uninhabitable  Therefore, little movement of animal species between Africa and Asia during glacial periods  When the world was warmer, grasslands and savannas replaced most deserts and animals were able to move between Africa and Eurasia more easily  Fossil record indicates that animal species moved mainly from Africa to Eurasia - Evolutionary transition from H. ergaster to modern humans occurred during the Middle Pleistocene - Eastern Asia: Homo erectus o Homo erectus, a hominin similar to H. ergaster, lived in eastern Asia during most of the Middle Pleistocene  Main morphological difference between H. erectus and H. ergaster lie in the skull  In H. erectus, skull is thicker, browridges are more pronounced, the sides of the skull slope more steeply, the occipital torus is more pronounced and there is a sagittal keel (longitudinal V-shaped ridge along the top of the skull)  Sagittal keel expands area of attachment of temporalis muscles in the paranthropines, but doesn’t serve this function in H. erectus  Homo erectus is known from sites in Java and China and persisted until 30 kya  Over this period, they changed very little 4 5  Most recent H. erectus fossils from eastern Asia are less like modern humans than are the African specimens of H. ergaster, which are 1 M years older  Presence of H. erectus fossils in eastern Asia suggests that this species mastered difficult environmental challenges o Homo erectus is associated with Mode 1 tools  Some think that differences in tool technology between eastern Asia and Africa provide evidence for cognitive differences between the two species  Others think that environmental differences may be responsible for tool differences - African and Western Eurasia: Homo heidelbergensis o Sometime during the first half of the Middle Pleistocene, hominins with larger brains and more modern skulls appeared  These individuals had substantially larger brains (1200-1300 cc) in relation to body size than H. ergaster had  Skulls also share a number of derived features with modern humans, including more vertical sides, higher foreheads and a more rounded back than H. ergaster had  However, also retained many primitive features, such as a long, low skull, very thick cranial bones, a large prognathic face, no chin and very large browridges  Bodies remained much more robust than modern human bodies are  Traditionally, paleontologists have referred to these hominins as archaic Homo sapiens  Scientists are unsure w
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