Toba catastrophe theory

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According to the Toba catastrophe theory, modern human evolution was affected by a recent large volcanic event. It was proposed by Stanley H. Ambrose[1] (http://www.anthro.uiuc.edu/faculty/ambrose/), of the University of Illinois at Urbana-Champaign. Knowledge of human prehistory is largely theoretical, but based in fossil, archeological, and genetic evidence.

Within the last three to five million years, after human and ape lineages diverged from the hominid stem-line, the human line produced a variety of human species. According to the Toba catastrophe theory, a massive volcanic eruption changed the course of human history by severely reducing the human population (called a 'bottleneck'). Around 75,000 years ago the Toba caldera in Indonesia erupted with a force three thousand times more powerful than Mount St. Helens.

According to Ambrose, this led to a decrease in the average global temperatures by 3 to 3.5 degrees Celsius for several years. This massive environmental change is believed to have created population bottlenecks in the various human species that existed at the time; this in turn accelerated differentiation of the isolated human populations, eventually leading to the end of all the other human species except for the branch that became modern humans (see volcanic winter).

Some geological evidence and computed models support the plausibility of the Toba catastrophe theory, and genetic evidence suggests that all humans alive today, despite their apparent variety, are descended from a very small population (see mitochondrial Eve). Using the average rates of genetic mutation, some geneticists have estimated that this population lived at a time coinciding with the Toba event.

According to this theory, after Toba, and when the climate and other factors permitted, humans once again fanned out from Africa migrating first to Indochina and Australia, and later to the Fertile Crescent and the Middle East. Migration routes to Asia created population centers in Uzbekistan, Afghanistan, and India. Divergences in skin color appeared, due to varied melanin levels, which were adaptations to the varying UV intensities around the world. Europe became populated by migrants from the Uzbekistan region when the last ice age ended and Europe began to be more hospitable.

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