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Out-of-Africa Theory: The Origin Of Modern Humans

Out-of-Africa Theory: The Origin Of Modern Humans. Presented By Adrian Padilla. Background Information. First species of Homo, Homo habilis, evolved in Africa around 2 million years ago.

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Out-of-Africa Theory: The Origin Of Modern Humans

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  1. Out-of-Africa Theory:The Origin Of Modern Humans Presented By Adrian Padilla

  2. Background Information • First species of Homo, Homo habilis, evolved in Africa around 2 million years ago. • Later, a descendant of Homo habilis, Homo erectus evolved (along with other hominids), and spread out of Africa. • Homo erectus gave rise to Homo sapiens around 100,000 to 200,000 years ago.

  3. Two Main Theories • Out of Africa Theory (OOA) – suggests that Homo erectus evolved into Homo sapiens in Africa, and then ventured out of Africa and dispersed to all around the world. • Multi-regional Evolution Theory – suggests that Homo erectus ventured out of Africa and then evolved into modern man in several different locations through out the world.

  4. Genetic Tools to Find the Answer • Fossil records • DNA sequencing • Mitochondrial DNA analysis (mtDNA) • Maternally inherited, therefore telling the story from the female side of human history • Y Chromosome analysis • Inherited down the paternal line, complementing the mtDNA • Microsatellite DNA analysis • Segments of tandemly repeated DNA with a short repeat length, usually 2-5 nucleotides

  5. Polymorphisms • Polymorphism - Existence of a gene in several allelic forms. • Polymorphic regions provide a very unique set of genetic markers for studying human origin and migratory patterns. • Used to construct a global evolutionary tree of modern man

  6. Mitochondrial DNA • Out-of-Africa hypothesis was first sketched out in 1987, based on mitochondrial DNA analysis • Suggested that modern man first appeared on the scene in eastern Africa about 150,000 years ago, and left between 35,000 and 89,000 years ago, eventually conquering the globe.

  7. Y Chromosomal DNA Study • Researchers looked at DNA samples from 12,000 male Y chromosomes in Asia. • Looking for 3 specific mutations on the Y chromosome known to have originated in Africa. • Researches found that every one of the 12,000 samples carried one of the three mutations or polymorphism

  8. Conclusion to the Y Chromosome Study • Little or no interbreeding of Homo erectus and Homo sapiens. • Individuals are descendants from Africa • Likely that the early African man emigrated to North Africa and made the leap to Asia and then to the rest of the world. • Indicates that modern humans of African origin completely replaced earlier populations in East Asia.

  9. More Y Chromosomal Studies • Samples were taken from men in 22 different geographical areas. • In countries that included Pakistan and India, Cambodia and Laos, Australia and New Guinea, America, Mali, Sudan, Ethiopia and Japan. • Researchers identified 167 polymorphic markers on the Y chromosome. • Markers were then assembled into 10 types, called haplogroups.

  10. Findings from Y Chromosomal Analysis • Assembled a phylogenetic tree showing a migration from eastern Africa into the Middle East, then southern and southeast Asia, then New Guinea and Australia, followed by Europe and Central Asia. • Some modern day men in Sudan, Ethiopia and southern Africa are the closest lineal descendants to the first Homo sapiens who left Africa • New Guinea and Australia were settled early in the process • Japan has remained in genetic isolation. Mutations are strikingly different from those of surrounding populations, they account by themselves as a specific haplogroup • Native Americans have a common ancestry with Eurasians and East Asians

  11. Microsatellite DNA Analysis • Researchers tried to find the estimated time of the deepest split of the human population. • Applied a genetic distance measurement to 30 microsatelite regions to construct a pylogenetic tree for 14 world-wid human populations

  12. What did they find? • In the tree obtained, the deepest root separated Africans from non-Africans. • Their calculations suggest the split ahppened an en estimated 115,000 to 156,000 years ago.

  13. mtDNA Analysis • Study on the complete mitochondrial genome. • 16,500 base pairs in each sequence • 53 people diverse from different geographical, racial, and linguistic backgrounds.

  14. Results • A tree rooted in Africa • Tree suggests that some Africans are closer to Europeans and Asians than to other Africans.

  15. Fossils • Archeologists find a fossil in Herto, Ethiopia dating about 160,000 years old • The oldest fossil found of Homo sapiens dates back 115,000, and is found in Israel. • Researches link the fossil found in Israel to the fossil in Herto, Ethiopia and other fossils found in Africa, based on physical characteristics of the skull.

  16. Conclusion • DNA sequencing evidence shows that modern humans originated in Africa and migrated north out of African, then eventually to the rest of the world. • Oldest fossils of modern humans are found in Africa dating around 160,000 years old.

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