SUMMARY: BIOLOGICAL EVOLUTION OF HUMANS

=Biological Evolution of Hominins= Biological evolution is the result of [https://www.pathwayz.org/Tree/Filter/SubTree/162#!o289 natural selection] acting upon whole populations over many generations. Biological evolution relies on mutations as a source of new characteristics and involves much longer time periods. A summary, highlighting some of the key changes throughout human evolution has been provided below. [image:http://i.imgur.com/gwaKIF7.png?1] '''''Pan troglodytes (chimpanzee)''''' •Cranial capacity 320-480cc •Quadrupedal / Brachiators •Prognathism -jaw protrudes from face, Large jaw / teeth •Barrel shaped rib cage / c-curved spine typical of quadrupedal lifestyle •Distribution: Central - Western Africa. •''Chimps are not our direct ancestors, but may resemble some of our earliest ancestors who had a similar lifestyle.'' [image:http://i.imgur.com/7kCod0B.png?1] '''''Australopithicines''''' •Cranial capacity 400-500cc •''africanus'' slightly larger than ''afarensis'' •Apelike Face; low forehead & brow ridge (slightly reduced in ''africanus'') •The Canines are smaller than chimps but still much larger than in modern humans •Pelvis and leg bones confirm bipedalism •Distribution: East Africa (Rift Valley) - South Africa [image:http://i.imgur.com/MtUPGP2.png?4] '''''Paranthropus group''''' •Cranial capacity 530cc •Extinct offshoot of the Australopithecines •Very robust skull with feature associated with a diet of tough fibrous / leafy material •Heavy brow ridge, zygomatic arches, large mandible (lower jaw) and sagittal crest •Distribution: South-East Africa [image:http://i.imgur.com/F3aQHcO.png?1] '''''H. habilis''''' •Cranial capacity 650-680cc •First to use tools (Oldowan) •Marked increase in cranial capacity •Bulge in Broca’s area (speech production) •Smaller narrower face with reduced jaw •Modern U-shaped jaw with narrower molars •Distribution: Rift Valley, East Africa [image:http://i.imgur.com/iAIcWXp.png?1] '''''H. erectus''''' •Cranial capacity 750 -1225cc •First to use fire and Acheulian tools •Marked increase in cranial capacity with a large difference between earlier erectus and later ones. •Development of Broca’s and Wernike’s areas of the brain possibly associated with rudimentary communication •Flat face with pronounced bow ridge •Distribution: Africa (H. ergaster), Asia & Europe (H. erectus) [image:http://i.imgur.com/yFvS0Rk.png?1] '''''H. neanderthalensis''''' •Cranial capacity 1600c •Larger brain than even H. sapiens but organized differently •Large occipital lobe / bun •Skull widest at base •Used more advances Mousterian flint tools •Further reduced teeth •Sloping forehead •Distribution: Europe and West Asia [image:http://i.imgur.com/hvNPpBh.png?1] '''''H. sapiens''''' •Cranial capacity 1400cc •Large brain with larger frontal lobes / cerebral cortex. •Skull is widest further up / higher •High vertical forehead •Further reduced teeth •No muzzle (prognathism) •Distribution: Global =Overall Trends: The Brain= Intelligence is not just a function of brain size: '''relative brain size''' appears to be more important (brain size compared to body size). While the pygmy ''erectus'' (''H. floresiensis'') appears to have such a small brain it actually has a brain comparable with erectus when we take into account the size of ''H. floresiensis''. [image:http://i.imgur.com/Q3mIQGT.png] The first of the two associated bursts in brain expansion is probably associated with the change to bipedalism, early tools and the use of fire. The second is probably associated with the further cultural developments of H.sapiens and ''H.neanderthalensis'' (such as much more sophisticated tools, language, etc). Modern humans have a brain volume three times larger than that predicted for an average monkey or ape with our body size. [image:http://i.imgur.com/frbWEk9.png?1] Another important factor is the '''organization''' of the brain, evident in the development of the areas concerned with spoken language. Bulges in two areas of the brain started to develop in '''''Homo erectus'''''. These two areas of the brain are associated with language and communication and have become highly developed in modern humans: •'''Broca’s area''' concerned with speech (controls muscles associated with pronunciation) •'''Wernicke’s area''' concerned with comprehension of language. These developments were at least partly afforded by a better diet resulting from the development of tool and the use of fire. The larger brains afforded from a higher calorie diet in turn aided cultural development (tools etc).