The differences among modern human populations developed in the evolutionary past. Scientists believe that humans evolved from apelike ancestors beginning about 5 million years ago. The predecessor of modern humans, Homo erectus, lived in Africa and migrated to Asia and Europe 1 million to 2 million years ago. Scientists generally agree that anatomically modern humans, Homo sapiens, evolved within the last 200,000 years. However, anthropologists disagree about how and where modern humans evolved. There are two major hypotheses about how modern humans evolved: the out of Africa hypothesis and the multiregional hypothesis.
According to the out of Africa hypothesis, modern humans originated in Africa in the last 200,000 years and spread from there to the rest of the world, including the Americas and Australia. This migration out of Africa to the rest of the world took place within the last 100,000 years and may have begun as recently as 50,000 to 70,000 years ago. Based on this hypothesis, the differences among modern humans today originated relatively recently—mostly after the great dispersal out of Africa, although some differences may have formed in Africa. According to the competing multiregional hypothesis, modern humans developed in parallel in Africa, Europe, and Asia over 1 million or 2 million years from existing populations of Homo erectus. In this scenario, differences between human populations originated in the distant past. The original support for the multiregional hypothesis derived from fossil evidence that suggested continuity of evolution between archaic humans in Europe, known as Neandertals, and modern Europeans. Certain fossils suggested similar continuity between archaic and modern humans in East Asia. The out of Africa hypothesis was first proposed based on genetic studies of a type of DNA known as mitochondrial DNA, which is inherited through the maternal line. Since then, studies of the Y chromosome, which is inherited through the paternal line, have confirmed the results of mitochondrial DNA studies. These studies show that living African populations have more genetic diversity than any other human groups, and that this diversity has been accumulating for perhaps 100,000 to 200,000 years. This finding implies that all modern humans are descended from a small population of Homo sapiens that lived in Africa 100,000 to 200,000 years ago. Analysis of mitochondrial DNA from a Neandertal fossil found in Germany also suggests that Neandertals did not contribute DNA to modern Europeans. Thus, evidence has been accumulating that modern humans are not descended from Neandertals living outside of Africa. Today, many geneticists and physical anthropologists see the balance of the evidence as strongly favoring the out of Africa hypothesis. For more information on the evolution of modern humans we can also find about Human Evolution in: "Theories of Modern Human Origins and Diversity".
Another important finding is that human genetic variation between groups, however defined, is small compared to that within groups. The data strongly support the idea that all living humans originated recently from a relatively small population—on the order of thousands or tens of thousands of individuals. All people share a strong genetic heritage, and are much more alike.
According to the out of Africa hypothesis, modern humans originated in Africa in the last 200,000 years and spread from there to the rest of the world, including the Americas and Australia. This migration out of Africa to the rest of the world took place within the last 100,000 years and may have begun as recently as 50,000 to 70,000 years ago. Based on this hypothesis, the differences among modern humans today originated relatively recently—mostly after the great dispersal out of Africa, although some differences may have formed in Africa. According to the competing multiregional hypothesis, modern humans developed in parallel in Africa, Europe, and Asia over 1 million or 2 million years from existing populations of Homo erectus. In this scenario, differences between human populations originated in the distant past. The original support for the multiregional hypothesis derived from fossil evidence that suggested continuity of evolution between archaic humans in Europe, known as Neandertals, and modern Europeans. Certain fossils suggested similar continuity between archaic and modern humans in East Asia. The out of Africa hypothesis was first proposed based on genetic studies of a type of DNA known as mitochondrial DNA, which is inherited through the maternal line. Since then, studies of the Y chromosome, which is inherited through the paternal line, have confirmed the results of mitochondrial DNA studies. These studies show that living African populations have more genetic diversity than any other human groups, and that this diversity has been accumulating for perhaps 100,000 to 200,000 years. This finding implies that all modern humans are descended from a small population of Homo sapiens that lived in Africa 100,000 to 200,000 years ago. Analysis of mitochondrial DNA from a Neandertal fossil found in Germany also suggests that Neandertals did not contribute DNA to modern Europeans. Thus, evidence has been accumulating that modern humans are not descended from Neandertals living outside of Africa. Today, many geneticists and physical anthropologists see the balance of the evidence as strongly favoring the out of Africa hypothesis. For more information on the evolution of modern humans we can also find about Human Evolution in: "Theories of Modern Human Origins and Diversity".
Another important finding is that human genetic variation between groups, however defined, is small compared to that within groups. The data strongly support the idea that all living humans originated recently from a relatively small population—on the order of thousands or tens of thousands of individuals. All people share a strong genetic heritage, and are much more alike.
0 comments:
Post a Comment