Human evolution Geological Epochs 65 54 mya First primates Eocene 54 34 mya First strepsirrhines 34 23 mya Oligocene Anthropoid radiation Miocene Hominoid radiation 23 5 0 mya 5 0 2 5 mya Pliocene Hominin radiation Pleistocene 2 5 0 1 mya 0 1 Holocene mya present The child skull radically changed then prevalent notions about human evolution in combining a centrally situated foramen magnum under the cranium and dentition of modern aspect with a small cranial capacity The discovery was contested because of 1 2 3 uncertainty surrounding the adult morphology of A Subsequent discoveries confirmed the place of A africanus in the human family tree The demonstrated that hominins acquired a bipedal gait before Bipedalism Cranium F M centrally situated under the cranium Postcranium Vertebral column with a and large lumbar vertebrae Pelvis with ilium bowl shape and stronger abductor muscles Hindlimb with a valgus knee enlarged femoral condyles a more robust ankle big toe aligned with other toes and two arches along the bottom of the foot Hypotheses concerning the evolution of bipedalism Unlikely allow hunting of grassland game Improved vigilance against predators and other threats Terrestrial feeding More impressive displays Provisioning by males for the females Likely Increased emphasis on USO s for consumption sun exposure However likely no single cause for the appearance of bipedalism Early hominin adaptations Cranium of C P3 honing complex Increase in size of dentition Reorientation of the dental arcade from shaped to parabolic in the degree of subnasal prognathism Increase in enamel Probable hominins None is fully accepted as an early hominin owing to inconclusive evidence about the presence of definitive bipedal adaptations Sahelanthropus mya Chad Orrorin mya Kenya Ardipithecus mya Ethiopia Australopiths Gracile vs robust variant Robust variant principally differs from the gracile variant in having a more robustly constructed cranium and mandible anterior dentition very small and an enlarged posterior dentition with very thick enamel Gracile and Robust and Locomotion positional repertoire with a skeleton that combines aspects of bipedalism with those consistent with arboreal locomotion Diet predominantly but occasionally supplemented by animal protein Australopiths likely used a variety of tools while engaging in extractive food behaviors on a level comparable to that of chimpanzees Other fast life history 1M 1F social organization Tool use Humans engage in more elaborate and complex 1 inter individual collaborations i e through triadic attention 2 transmission of knowledge i e through teaching permitting cultural transmission 3 tool using behaviors than chimps Introduction and use of a diverse toolkit by hominins replaces the need for anatomical adaptations to accommodate certain food extractive behaviors observed in other animals e g flesh cutting bone crushing digging weapons etc This has been called evolution Stone tool use Humans are not the only animals that make and use stone tools Human made tools can be distinguished from rocks that acquired a tool like appearance through natural causes by a set of diagnostic features Taphonomy has been crucial for 1 distinguishing between carnivore and stone tool cutmarks and 2 assessing the time of when the early stone tool makers had access to the animal carcass i e early vs late access The oldest stone tools are part of the Lomekwian Tradition 3 3 mya and is characterized by bipolar core reduction Subsequent technologies e g Oldowan Acheulean Mousterian etc are reclassified in a revised scheme introduced by John Shea that emphasizes stone tool producing behaviors over attributes of the stone tools themselves The modes are reclassified according to a letter and number combination with Oldowan being denoted as Mode C the Acheulean as Mode E1 2 Levallois as Mode F and the blade technology characteristic of the Upper Paleolithic as Mode G It cannot be determined with certainty which hominin made the oldest stone tools but it may have been an australopith Earliest archaeological sites are found in but interpretations concerning the association between the stone tools and broken bones have changed through time ranging from human agency carnivore action or as the product of geological processes Current evidence favors the interpretation that the earliest stone tool makers were active scavengers that occasionally hunted Homo differs from australopiths in having a Bigger brain Smaller teeth More parabolic dental arcade More rounded skulls Less prognathic face Early Homo Taxonomic diversity Homo KNM ER 1813 Homo KNM ER 1470 Locomotion and life history more comparable with australopiths than with Homo erectus Homo erectus Out of Africa What facilitated the hominin dispersal out of Africa and into Eurasia Rejected acquisition of biface technology following other animals out of Africa change in male female relationships increase in brain and or body size Supported increased kin selection opportunities because of the presence of older individuals i e Wisdom of the Aged and increased meat consumption The fossil evidence of H erectus suggests a rapid geographic dispersal out of Africa and into Asia shortly after its first appearance in the fossil record Temporal trends in Homo erectus Increase in brain size Increase in body size Initial reliance on Oldowan stone tool technology but later develops the Acheulean biface stone tool technology 1 6 mya The Acheulean principally differs from the Oldowan in demonstrating increased standardization and efficiency which would have required increase cognitive functions Anatomy Increase in brain and body size presence of an intermembral index similar to modern humans i e short forelimbs relative to length of the hindlimbs and and pelvis Behavior Changes in anatomy are consistent with endurance running as an adaptive innovation of Homo erectus relative to australopiths and Early Homo Increased brain and body size suggests an increase decrease in the amount of meat that was included in the diet The expensive tissue hypothesis proposes a link between brain and gut size suggesting that the elevated energetic demands of an increase decrease brain size were energetically offset by an increased reliance on high quality easy to digest food such as meat or cooked foods The latter has also been proposed to account for the reduction in tooth size and body hair as well as an increase in social interactions and complexity Use
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