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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. • 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.
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.
Genetic Tools to Find the Answer • Fossil records • DNA sequencing – Mitochondrial DNA analysis (mt. DNA) • Maternally inherited, therefore telling the story from the female side of human history – Y Chromosome analysis • Inherited down the paternal line, complementing the mt. DNA – Microsatellite DNA analysis • Segments of tandemly repeated DNA with a short repeat length, usually 2 -5 nucleotides
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
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.
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
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.
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.
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
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
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.
mt. DNA Analysis • Study on the complete mitochondrial genome. • 16, 500 base pairs in each sequence • 53 people diverse from different geographical, racial, and linguistic backgrounds.
Results • A tree rooted in Africa • Tree suggests that some Africans are closer to Europeans and Asians than to other Africans.
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.
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.