Evolution of Homo sapiens
The emigration from Africa is traced back to 50, 000 years ago viathe Eurasian continent. Modern humans are thought to have originatedsome 200, 000 – 250, 000 years with some school of thought extendingit two million years ago (Tattersall 487). Two camps, multiregionalor continuity theory and replacement or “Out of Africa,” conteststhe origin of modern humans (Tattersall 487). The continuity campextends its origin of modern man from H. Erectus throughsuccessive generations that sprang from respective regions, that is,Asia, Africa, and Europe. The backers of this theory trace continuityin the morphology of successive populations in the Paleolithic era.
This model proposes parallel changes in respective penecontemporarypopulations facilitated by genetic crossing which maintained closebond between the species. The replacement perspective believes in twodifferent hominid migrations from Africa to Europe and Asia with theH. Erectus preceding the H. Sapiens. The theorysuggests that H. Sapiens replaced the H. Erectus withinsignificant interbreeding to generate the “modern” humans. Thisreplacement may have been aided by higher adaptive capability orcompetitive extermination of the native H. erectuspopulations.
Thus, the proponents of the replacement theory seek to identifysimilarities whereas the continuity theorists look for thedifferences in the regions’ populations. While the continuitytheory is regarded as a racist theory that seeks for the differences,the replacement theory is seen as conforming to the religiousperspective of the origin of “modern” humans. Proponentevolutionary theorists disregard this and propose speciation tookplace in Africa rather than in separate regions as proposed by themultiregional model.
Current findings suggest that “modern” humans originated asevident from the oldest fossil records of H. sapiens fromEthiopia dating back to 130, 000 years with no other fossil recordsof H. sapiens older than that supporting the replacementtheory (Tattersall 488). Genetic studiesalso corroborate with this finding on the origin of the modern manwith modern Africans demonstrating more diversity than Asians andEuropeans. Mitochondrial DNA, like any other DNAs, accumulatesmutations with time, and these mutations drive diversity. Theexistence of other species that may have preceded modern humans isbacked by genetic and archaeological evidence among other evidence.One of the earliest species to be discovered in 1974 isAustralopithecus afarensis, a 3.2 million-year-old ape“Lucy.” It had both human and ape features and legs suited towalk upright (Leakey 433).
The earliest hominids to migrate from Africa to Asia and Europe overa million years ago underwent genetic drift and natural selection todevelop into the Peking and Java man in Asia, and Neanderthals inEurope. The two hominids are collectively referred as HomoErectus, and possess anatomical differences with the H.sapiens. Neanderthals were short, broad and sturdily built,characterized by large and long cranial vault and well developeddouble-arched brow ridge (Tattersall 488).The short and tall globular braincase is a distinguishing feature ofthe H. Sapiens from the two hominid species. This globularbraincase has anteroposteriorly short and delicate that ischaracteristically retracted (Tattersall and Klein 16018). The thoraxis barrel –shaped in H. Sapiens, unlike the Neanderthal ribcage that is conically shaped. The H. Erectus, in Europecalled Neanderthals are believed to have migrated from Africa in thefirst hominid migration over a million years ago.
Modern Homo sapiens distinguished by vertical foreheads,slight brow ridges and high, short braincases have been in existencefor more than 90,000 years. The H. Sapiens has a large, unlikeother earlier hominid populations. The ability to have cognition andcomplex use of symbolic language differentiate H. Sapiens fromother species. This is in addition to having Cultural Revolution thatmakes the modern H. Sapiens to not control its biologicalfuture, but shape and remodel the environment for its own survival(Tattersall 490). Historians believe Homo sapiens migrated tothe Western hemisphere during the Late Pleistocene, not later than30,000 ybp (Hey965). This was due to a reduction in the sealevel and the creation of a land bridge between Northeastern Asia andNorthwestern America following Last glacial maximum in a conditionreferred as the Beringia. The first H. Sapiens tooccupy the Western hemisphere was referred as the Amerindpeople (Bradleyand Stanford 460).
Different theories seek to explain the movement and spread of themodern H. Sapiens across the globe. The first theory, thereplacement model, posits that African Homo sapiensmigrated out of Africa to different regions of the world graduallyreplacing the Neanderthals, Java, and Peking man who previouslyoccupied those lands. The second theory is the multiregional modelthat postulates independent evolution of humans across the respectiveregions to give rise to modern H. Sapiens. The geneticcrossing between the different regions (Homo Sapiens 1) preventedextensive speciation. The third theory is a combination of the firsttwo theories, proposes that modern humans may have risen through anassimilation model where early hominids populations interbred witheach other. The replacement model is the dominant theory of therepopulation of the world with Homo sapiens. Homo sapiensstarted adopting settlement lifestyles in the late Paleolithic era,around 10, 000 B.C – 5, 000 B.C. These settlements were organizedin permanent dwellings such as long houses accommodating severalpeople or simple structures for individual families. The permanentsettlements such as the Natufian in Eastern Mediterranean and theChinook society and Jomon society in North American and central Japanrespectively were organized on the basis of availability of food(Bentley and Ziegler 14).
TheNeolithic revolution is a prehistoric transition from hunters andgathering to farming, and is marked by social and economic changestaking place around 10,000 years ago. Several theories have beenfronted to explain the rise of agriculture such as the overkillhypothesis that postulates that excessive hunting led to thePleistocene extinction of large mammals. The advent of agricultureled to settlements that, in turn, led to specialization andurbanization. These settlements were the birthplace of earlycivilization and the use of more advanced tools (Weisdorf 561).Settlements led to the concentration of population leading todiseases and rise of specialization and a ruling class among thepopulation. Agriculture also led the Homo sapiens to be moredependent on climate for their livelihood.
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