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24 25 the miGration of Genes out of Africa How do the gene pools of a species behave over wide areas Changes can often begin in areas isolated through physical or behavioral causes, so that localised subpopulations become hot spots of new genetic information. Genes can also drift about within species, as individuals explore, travel and fall in love. The evolutionary history of humanity shows combinations of both hotspotting and ubiquitous drift in the fossil record, smoothly progressing in some periods, while in others it is more staggered. Hotspotting has resulted in the many races of humans, while ubiquitous drift within those races has resulted in the relatively uniform genetic characteristics that can be seen. The study of genes has enabled various maps of humankind to be plotted. Circular mitochondrial DNA, for example, is only inherited from mothers, so avoids the shuffling of meiosis, and remains virtually unchanged down the generations. Studies of mitochondrial DNA have revealed that 99 of Europeans are descended from just seven women known as clan mothers living at different sites in Europe at different times during the last Ice Age. Globally, all humans are now known to be descended from a single ancestress living in Africa about 200,000 years ago. Similar studies of the Ychromosome, which is only passed from father to son also virtually unchanged, have revealed that 99 of Europeans are descended from just five men clan fathers, living during the last Ice Age. All humans are now known to descend from just one man, living in Africa about 70,000 years ago. Above Studies of mitochondrial DNA and the Ychromosome have revealed the path by which humankind left Africa, by a northeasterly route, roughly 65,000 years ago. The ancestors split up, some heading south, others heading east, then northwest. Europe was populated around 40,000 years ago, and the Americas 25,000 years ago. Above Studies have revealed that we are all descended from a handful of ancestors. For instance, the Ychromosome of Native American peoples has revealed a single Native American man, from whom 85 of all Native Americans in South America, and half those in North America, are directly descended.
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