Toba catastrophe theory
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According to the Toba catastrophe theory, modern human evolution was affected by a recent, large volcanic event. The theory was proposed by Stanley H. Ambrose of the University of Illinois at Urbana-Champaign.[1][2]
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[edit] History
Within the last three to five million years, after human and other 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. This may have occurred when around 70–75,000 years ago the Toba caldera in Indonesia underwent a category 8 or "mega-colossal" eruption on the Volcanic Explosivity Index. This released energy equivalent to about one gigaton of TNT, three thousand times greater than that of Mount St. Helens. According to Ambrose, this reduced the average global temperature by 3 to 3.5 degrees Celsius for several years and may possibly have triggered an ice age.
This massive environmental change is believed to have created population bottlenecks in the various species that existed at the time; this in turn accelerated differentiation of the isolated human populations, eventually leading to the extinction of all the other human species except for the branch that became modern humans.
[edit] Geological evidence
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, perhaps between 1,000 and 10,000 individuals.[citation needed]
Using the average rates of genetic mutation, some geneticists have estimated that this population lived at a time coinciding with the Toba event (see also Mitochondrial Eve and Y-chromosomal Adam).
[edit] Migration issues
According to this theory, humans once again fanned out from Africa after Toba when the climate and other factors permitted. They migrated 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.
Possibly substantial differences in skin color appeared as a result of varied melanin levels as local adaptations to varying ultraviolet intensities.
Europe became populated by migrants from the Caspian Sea region when the last ice age ended and Europe became more hospitable.
[edit] See also
[edit] References
- ^ Stanley H. Ambrose (1998). "Late Pleistocene human population bottlenecks, volcanic winter, and differentiation of modern humans". Journal of Human Evolution 34 (6): 623–651. DOI:10.1006/jhev.1998.0219.
- ^ Ambrose, Stanley H. (2005). Volcanic Winter, and Differentiation of Modern Humans. Bradshaw Foundation. Retrieved on 2006-04-08.
