BILD 3 - Lecture 22

BILD 3 - Lecture 22 - Human Genetic Diversity All humans...

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Human Genetic Diversity All humans living today are closely related genetically. The recent completion (or near-completion) of the Human Genome Project, in which about three quarters of the three billion bases in the human genome have been sequenced, shows that two individuals drawn at random from our species share 99.5% of their sequence. Two individuals from different continents share approximately 99.3%, showing that racial differences count for little and that most of our limited diversity is present within racial groupings. In contrast, humans and chimpanzees show about a 96% match, indicating that humans and chimpanzees have diverged about eight times further than unrelated human individuals have. Preliminary evidence from the chimpanzee genome suggests that humans and chimpanzees have comparable amounts of genetic diversity. Our diversity may have been shaped strongly by natural selection. Recent analyses by John Hawks and his colleagues, using data from the human HapMap project, suggests that our evolution has actually been accelerating recently. The HapMap project has accumulated information on single nucleotide polymorphisms in our species. Two million of these polymorphisms, scattered throughout the genome, are now known and mapped. Hawks et al. looked for signs that alleles at different polymorphic loci had recently increased in frequency in our species, in the process dragging along alleles at other linked polymorphic loci:
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This figure shows the kind of pattern that would be expected if an allele (green circle) becomes strongly favorable and increases quickly in the population. It will drag along the alleles that it happens to be linked with at nearby loci. About 2,000 such polymorphisms have been found, in European and African populations. The African selected alleles began to spread shortly before the European ones, presumably because African populations have older origins. (Their age was estimated by how small the blocks of genes that are dragged along with the polymorphisms are; the smaller the blocks, the more time has passed and the more they have been broken up by genetic recombination.) The genes involved are unknown for the most part, but some genes in the selected regions are known to be involved in brain function and in disease resistance.
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The Origin of Present-Day Cultures One of the enduring mysteries of human evolution is the question of the origin of modern cultures. Throughout most of the archeological record of the Old World, the stone tools and other artifacts that have been found are simple and lacking any decoration. Then, starting about 40,000 years ago in Europe and the Middle East, slightly later in southern Africa and perhaps even slightly earlier in Australia, decorated artifacts and representational art (pictures and carvings of humans, animals and natural scenes) appeared relatively suddenly (figure below). This remarkable event has been termed the “Great Leap Forward” by Jared Diamond.
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