Chapter 8 Outline: Early Hominins - Kottak Introduction to Anthropology
Chapter 8 Outline: Early Hominins - Kottak Introduction to Anthropology SOCA 105
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Introduction to Anthropology Notes 1042015 Chapter 8 Early Hominins INTRODUCTION UNDERSTANDING OURSELVES 0 Despite their name quotmonkey barsquot illustrate a form of locomotion speci c to humans and apes that is known as brachiation the use of the arms to swing hand over hand Monkeys use all four limbs as they run across the tops of branches 0 Bipedalism is another form of locomotion that humans use We rely far more on bipedalism than brachiation o the loss of this ability perhaps as a result of a hip fracture can have devastating consequences Kottak uses the example of his own mother39s struggles with a broken hip to illustrate the continued importance of bipedalism WHAT MAKES US HUMAN o Hominin is used to designate the human line after its split from ancestral chimps 0 Hominid refers to the taxonomic family that includes humans and the African apes and their immediate ancestors Used in this book when there IS doubt about the hominin status of the fossil o Bipedalism o Ardipithecus the earliest widely accepted hominin genus Postcranial material from them indicates a capacity for upright bipedal locomotion Ardipithecus pelvis appears to be transitional bw one suited for arboreal climbing and one modi ed for bipedalism walking on two legs 0 Bipedalism upright twolegged locomotion Key feature differentiating early hominins from apes Bipedalism is more than ve million years old Bipedalism traditionally has been viewed as an adaptation to open grassland or savanna country Advantages of Bipedalism Abilities to see over long grass and scrub To carry items back to a home base 0 To reduce the body s exposure to 60 more solar radiation less body surface is exposed to the sun 0 More energy ef cient o Brains Skulls and Childhood Dependency 0 Early hominins had very small brains 0 Brain size has increased during hominin evolution especially with advent of the genus Homo 0 Compared with the young of other primates human children have a long period of childhood dependency during which their brains and skulls grow dramatically 0 Natural selection has struck a balance bw the structural demands of upright posture and the tendency toward increased brain size Introduction to Anthropology Notes 1042015 0 Tools 0 Given what is known about tool use and manufacture by the great apes it is likely that early hominins shared this ability as a homology w the apes o Bipedal locomotion also allowed early hominins to carry things Permitted use and transport of tools and weapons against predators in an open grassland habitat 0 Teeth 0 One example of an early hominin trait that has been reduced during subsequent human evolution is big back teeth and thick teeth enamel that adapted for the brous savanna39s gritty vegetation o The rotary motion associated with chewing such vegetation also favored reduction of the canines and rst premolars bicuspids CHRONOLOGY OF HOMININ EVOLUTION o The term hominin is used to designate the human line after its split from ancestral chimps Hominid refers to the taxonomic family that includes humans and the African apes and their immediate ancestors 0 Although recent fossil discoveries have pushed the hominin lineage back to almost six million years ago humans actually haven39t been around too long when the age of the Earth is considered 0 Although the rst hominins appeared late in the Miocene epoch for the study of hominin evolution the Pliocene 52 mya Pleistocene 2 mya 10000 BP and Recent 10000 BP present epochs are most important Until the end of the Pliocene the main hominin genus was Australopithecus which lived in subSaharan Africa By the start of the Pleistocene Australopithecus had evolved into Homom WHO WERE THE EARLIEST HOMININS o Sahelanthropus Tchadensis Hominoid o Discovered in July 2001 in northern Chad Africa determined to be 67 my old 0 Oldest possible human ancestor yet found 0 Also known as quotToumaiquot 0 Discovery team identi ed the skull as that of an adult male with a chimpsized brain heavy brow ridges and a relatively at humanlike face 0 Habitats included savanna forests rivers and lakes 0 Toumai blends apelike and human characteristics a chimpsized brain and a smaller snout than that found in chimpanzees shorter canine Introduction to Anthropology Notes 1042015 teeth than in apes and thicker tooth enamel than is found in chimpanzees All of which suggest a diet of not just fruits but also tougher savanna vegetation Placement of the foramen magnum implies that this species moved bipedally o Orrorin Tugenensis Hominid O O O 0 Found in January 2001 Kenya determined to be 6 my old Thirteen fossils formed least ve different individuals Chimpsized creature that climbed easily and walked on two legs when on the ground Teeth are more like a female chimp that human yet its bipedalism and other dental and skeletal features lead researched to assign them to hominin lineage 0 Ardipithecus Hominins O O Lived bw 58 and 55 mya Ardipithecus Kadappa lived in the late Miocene In 2009 the discovery of a fairly complete skeleton of Ardipithecus Ramidus was announced Determined that the found skeleton Ardi the earliest known hominin skeleton was almost 12 my older than Lucy the previous holder of that distinction Skeleton appears to be transitional between earlier arboreal primates and later terrestrial ones Although the pelvis would have allowed Ardi to walk the presence of strong hamstring muscles for climbing the lack of arched feet plus having long arms and short legs betray her arboreal heritage Ardi appears to have lived in a moist woodland environment Based on teeth that have been found at the site she probably had an omnivorous diet less dependent on fruits than that of living apes While the relationship between Ardipithicus and Australopithicus has not been determined Ardi is considered a plausible ancestor of Australopithicus o Kenyanthropus Hominins 0 Found in Kenya determined to be 35 my old Introduction to Anthropology Notes 1042015 Kenyanthropus Platyops was identi ed by Maeve Leakey and her research team in 1999 based on fossils from northern Kenya Leakey views Kenyanthropus as showing that least two hominin lineages existed as far back as 35 mya 0 One was the wellestablished fossil species Australopithecus Afarensis 0 According to Leakey A Afarensis may not be a direct human ancestor after all Kenyanthropus has a attened face and small molars that are strikingly different from those of afarensis suggesting to Leakey that it represents a new taxon THE VARIED AUSTRALOPITHECINES o Australopithecines common term for all members of the genus Australopithecus The seven species of Australopithecus are anamensis 4239 mya afarensis 3830 mya africanus 3020 mya garhi 25 mya robustus 2010 mya boisei 2610 mya sediba 198178 mya NPP PP P gtppgtgtgtgt o Australopithecus Anamensis o Anamenis earliest known Australopitehcus speciies 4239 mya Kenya 0 Bipedal Hominin from northern Kenya whose fossil remains were found by Maeve Leakey and Alan Walker in 1995 A Anamenis may be ancestral to A Afarensis which is usually considered ancestral to all the later Australopithecines as well as to Homo o Australopithecus Afarensis 0 Au Afarensis early Australopithecus species 3830 mya Ethiopia Tanzania Supports a very recent divergence from a common ancestry with the apes bc of the clearly apelike features found in all three species 0 In 2000 another A Afarensis skeleton quotLucy39s Babyquot was found in Ethiopia This very complete skull is the world39s oldest fossil child and sheds light on the growth processes of A Afarensis39 brain Introduction to Anthropology Notes 1042015 LIKE apes and UNLIKE modern humans A Afarensis had sharp canine teeth and the lower premolar was pointed and projecting to sharpen the upper canine These teeth were smaller than ape canines Fossils of molars and jaws indicate the beginnings of adaptation to a coarse savanna diet Cranial remains show that A Afarensis was still remarkably apelike in some respects Its brain capacity was only slightly larger than a modern chimpanzee39s and the jaw and overall body size indicate considerable sexual dimorphism Postcranial remains particularly the pelvis leg feet and spinal entry into the skull all indicate bipedalism and are thus clearly hominin A Anamensis 42 39 mya and Ardipithecus 58 44 mya remains also indicate bipedalism thus bipedalism predates A Afarensis A Afarensis young probably depended on their parents for a relatively long time facilitating social learning 0 Gracile and Robust Australopithecines 0 Relationship bw the graciles A Agricanus and the robusts has been debated for generations but remains unresolved One model has Fricanus and Robustus as separate species whose life spans were least partly contemporaneous Another model has Africanus and Robustus as sequential w Africanus being ancestral to Robustus A third model has BOTH groups as part of a single polytypic species representing opposite extremes of variation wn that species A similar debate obtains for A Robustus versus A Boisei but it is more likely that boisei developed from robustus into a separate hyperrobust species that was highly specialized giant molars a sagittal crest and relatively small front teeth for a savanna vegetation diet Sexual Dimorphism in the australopithecines is evident through observing the size of the canine teeth as well as other features in both A Afarensis and A Africanus The skulls jaws and teeth of the australopithecines indicate that their diet was mainly vegetarian requiring extensive crushing and grinding The 1985 discovery of the socalled black skull dated to 26 mya has made for more possible models of the divergence between Homo and Australopithecus The black skull thus called because of the coloration lent by the mineral content of the fossil itself was a surprising mixture of Introduction to Anthropology Notes 1042015 australopithecine features particularly given its relatively early date Alan Walker and Richard Leakey view the black skull as a very early hyperrobust A boisei whereas other scholars have assigned the black skull to its own species A aethiopicus o It had an apelike jaw and a relatively small brain o It had a sagittal crest on the top of the skull previously associated with the relatively modern hyperrobusts like A boisei 0 Brain size increased only slightly from A Afarensis 430 cm3 to A Africanus 490 cm3 to A Robustus 540 cm3 These gures can be compared with an average cranial capacity of 1350 cm3 in Homo Sapiens THE AUSTRALOPITHECINES AND EARLY HOMO o By 2 mya the ancestors of Homo became reproductively isolated from the later australopithecines such as A robustus and A boisei which coexisted with Homo 0 We still don t know why how and exactly when Australopithecus and Homo split 0 Contemporaneous 2 mya sets of teeth very different in size constitute the earliest evidence for a split between the ancestors of Homo H habilis and the later australopithecines such as A boisei o The distinctive early Homo trends are a rapid increase in brain size increasingly elaborate toolmaking and increasing emphasis on hunting and gathering 0 There remains considerable debate as to when and in what population these trends led to speciation from an australopithecine to Homo habilis o Johanson and White 1979 propose that A afarensis effectively produced two populations which became reproductively isolated and evolved into the other australopithecines and Homo habilis 2 mya 17 mya OLDOWAN TOOLS o The simplest obviously manufactured tools were discovered in 1931 by LSB and Mary Leakey at Olduvai Gorge Tanzania That locale gave the tools their name Oldowan pebble tools 0 The tools consist of cores used to produce sharp akes that could be used for cutting The core could then be used as a chopper Core tools and choppers are the most common stone tools found early African tool sites May have been used for food processing particularly to dismember game carcasses and break open marrow cavities Oldowan sites have also yielded pieces of bone and horn with scratches indicating that they were used for digging up tubers or insects Though Homo Habilis has been identi ed as the rst hominin to make tools the identity of the earliest stone toolmakers has been a subject of much debate 0 A recent discovery suggests it was likely that one kind of australopithecine also made and habitually used stone tools Introduction to Anthropology Notes 1042015 0 Au Garhi and Early Stone Tools 0 Au Garhi tool making Australopithecus species 2625 my old Ethiopia In 1999 a new hominin species Australopithecus garhi associated with stone tools and the remains of butchered animals was found in Ethiopia The new fossils date to 25 mya o This nd is signi cant for three reasons 1 It added a new potential ancestor to the human family tree 2 It demonstrated that the thighbone elongated 1 million years before the forearm shortened to create current human limb proportions 3 It showed that early stone tools were designed for obtaining meat and marrow from big game suggesting a dietary revolution 0 The discovery of early stone tools with A garhi provides evidence for emergent cultural capacities which grew exponentially with the appearance of Homo 0 With increasing reliance on hunting toolmaking and cultural abilities Homo became the most ef cient exploiter of the savanna ecological niche o The last australopithecines such as A boisei may have been outcompeted and forced into ever more marginal areas 0 Oldowan Hominins at the Kanjera Site 0 Comparisons with chimps and bonobos suggest that hominins always have lived in social groups composed of multiple males and females Our closest relatives chimps and bonobos lack pair bonding
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