Modern insanın evrimine ilişkin teorilerin değerlendirilmesi: Türkiye örneği
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2010
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Sosyal Bilimler Enstitüsü
Abstract
Admittedly, one of the most hotly debated issues in contemporary paleonanthropology is the modern human origins. This debate -which has also paved the way for the emergence of paleonanthropology as a science- has been tackled and interpreted by several different scientific societies with various approaches. In order to discuss on a scientific basis, potential results and consequences should necessarily be assisted and supported by data from other disciplines and other field of studies as well. In this context, along with paleoanthropological evidences, namely fossil materials, supportive elements from archaeological and genetic studies are obviously required. In recent years, particularly in light of advancements in dating and genetic studies researchers have been able to construct relatively more reliable assumptions and evolutionary models regarding to modern human origins. While most of these views are consist of recently revived and reviewed versions of previously put forward models, others are based on new standpoints. In light of ongoing debates for years, -despite the fact there have been various sub-model proposals which are based on different structural foundations- models regarding to modern human origins have been grouped under two main categories.One of these models has been proposed and supported by researchers like F. Weidenreich, M. Wolpoff and A. Thorne. It has been titled as Multi Regional Evolution model. According to this model, migration and admixture -on a genetical basis- are not considered on a substantial basis. Without losing interspecific gene flow, archaic species that had been dispersed severalparts of the Old World through migration acts initiated by Homo erectus populations approximately 1, 8 - 1, 7 million years ago, almost simultaneously evolved into archaic Homo species then ultimately to Homo sapiens. The competing model, which is mostly supported by genetical studies, is called the Out of Africa model (also known as Recent African Origin model) and it is championed by researchers like A. Wilson, R. Cann, C. Stringer, P. Andrews, D. Cameroon and C. Groves. According to Out of Africa model, about 200.000 and 150.000 years ago an archaic form of Homo genus emerged in East Africa (Ethiopia today), by means of migration it dispersed and reached Middle East around 80.000, Europe 50.000, Australia 40.000 and ultimately North America 14.000 years ago. It has been argued that this species replaced other archaic forms that had previously dispersed to many regions of the Old World, thus formed a direct ancestral lineage to what we regard it today as Homo sapiens sapiens.Genetical data which are seemingly support traditional Out of Africa evolution model have been attained from mtDNA (mitochondrial DNA) studies. Lewin (2003), emphasizes the fact that the mtDNA's relatively small and circular-shaped structure has approximately 510 times faster mutation rate than that of long and linear molecules of nuclear DNA. However, by contrast with the nuclear DNA is that inherited from both mother and father, mtDNA only inherited from mother to daughter therefore, it functions as a comparatively more purposive and reliable molecular clock. Genetical differences and diversification observed in Sub-Saharan Africa emphasizes that Africa has had far more extended history of human presence than those of any other parts of the world. Apart from mtDNA, Y-chromosome is the only genetical material that passes on directly from one of the parents to the descendant. Y-chromosome inherited from father to son yet it hardly reflects any signs of genetical diversification among the contemporary populations throughout the world today. Proponents of the Out of Africa model present it as aproof that Homo sapiens in the past -possibly quite recently- has descended from an extremely small population. Quite recently, it has been argued that studies which have undertaken on the 12th chromosome indicates that the 12th chromosome's structure exhibits higher diversification among Sub-Saharan African populations while other regions of Africa -like northwest Africa- display far less diversification as the case with the rest of the world that almost lacks this character.Proponents of the Multi Regional Evolution model hold that, not only the outcomes of the mtDNA and Y-chromosome studies that are capable enough to help us through the impasse of modern human origins debate but also -and perhaps most essentially- fossil materials which are stretch over millions of years should be considered as a referral source. Multi Regional Evolution model posits that humans whom can be described as a modern had started to made their way out of Africa around 1.8 million years ago and descended from previously dispersed Homo erectus populations by gene flow retaining both their anatomical, social and cultural traits acquiring regional continuity. Supporters of the Multi Regional Evolution model respond to the replacement phenomenon which Out of Africa model proposed, as -at least among archaeological material- it should have been observed that replacement had been taking place yet there aren't any signs of replacement have been observed in Asia -which takes up the majority of the Old World-. While hand axes were widely being utilizing in Africa, in East Asia hand axes haven't been involved in the tool kit by any means either before or after the migration wave out of Africa. It's been argued, by this, lower genetic diversification among today's human population, in other words occurrence of higher frequency of genetic similarity are the proofs that reveal the intimate genetical linkages, relatively recent archaic relationships and presence of mechanisms like genetic exchange or gene flow.
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evrim, teori, Türkiye örneği