Earliest humans walked bipedally But had small brains Why did brains not get large until later First big jump in brain size cranial capacity was with the beginning of the genus Homo but there is a small increase among Australopithecines For comparative purposes brain size in ml Modern human 1150 1750 x 1325 Homo habilis 500 800 x 680 20 50 bigger A afarensis 380 500 x 440 10 bigger Modern chimp 285 500 x 390 Radiator Theory The idea that brains could not expand until a new pattern of blood flow developed to keep the brain from getting too hot despite standing upright In the fossil record find two different patterns of blood drainage from the cranium Gracile Australopithecine and Homo lineage like ours today two alternate drains Robust Paranthropus lineage is different only one major drain The Radiator Theory applies to Australopithecus fossils from that point on we see the double blood drainage system But a second theory addresses the huge jump in cranial capacity we see with Homo Expensive Tissue Hypothesis Is associated with both a change in the rib cage shape first seen in Homo erectus AND a change in diet We ll talk more about this hypothesis next week when we learn about Homo erectus So when did humans first develop language Are there any physical clues that could tell us Are there any cultural clues at what point MUST they have had language to do the things they did When did language develop and what evidence could we see in the fossil record 1 Does vocal apparatus at basicranium allow speech Basicranium bones at base of skull 2 Do we see modern brain structure and organization Left hemisphere controls language and ability to use symbols 3 At what point did hominids have something to communicate about that would require language Modern chimp modern human 1 Basicranium anatomy modern human s allows greater range of sounds because is flexed Australopithecines do not have this anatomy yet But we can t yet reconstruct early Homo vocal tract Feder Park 2001 253 2 Endocasts show asymmetrical brains and language associated areas in all Homo and Australopithecus as well as modern chimpanzees not all exactly alike 3 It could be that it is not until Homo that a social need developed for language
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