The Toba Catastrophe Theory suggests that a supervolcano eruption 75,000 years ago caused a population bottleneck in humans, leading to low genetic diversity. Geological and genetic evidence supports the theory, but it is still debated in the scientific community.
The Toba Catastrophe Theory is the idea that a population bottleneck in mankind’s past, inferred from genetic analysis, was caused by an eruption of a supervolcano 75,000 years ago at Lake Toba, present-day Indonesia . The Toba catastrophe theory was first proposed in 1998 by Stanley H. Ambrose of the University of Illinois at Urbana-Champaign. According to genetic analysis, human genetic diversity is actually quite low compared to similar species, and all humans living today are descended from a population of 1,000 – 10,000 breeding pairs that lived 50,000 – 150,000 years before the present. This is called a population bottleneck.
The Toba catastrophe theory is supported by geological evidence (ice cores from Greenland) showing substantial change in global climate over time. Genetic analysis of human hair lice also supports the idea. Anecdotal evidence of 1816, the so-called “Year Without Winter” – caused by the colossal eruption of Mt. Tambora, also in Indonesia, shows that human populations suffer huge losses during volcanic winters. The Mt Toba eruption released about 2800 cubic km (670 cubic miles) of pyroclastic material, an 8 on the Volcanic Explosivity Index (“mega-colossal”), about 30 times greater than the largest volcanic eruption of the past 2,000 years.
According to Dr. Ambrose, global temperatures dropped about 5°C (11°F) immediately after the eruption. This was due to dust high in the atmosphere obscuring the Sun, and the effect would last for six years. Ambrose further argues that the explosion of Mt. Toba was the cause of the end of the last interglacial period, which, perhaps not surprisingly, ended around the same time as the eruption. The most severe decrease in temperature would have occurred for the first thousand years after the eruption, which is when the bottleneck is supposed to have occurred. A nineteen thousand year glacial period followed, the Würm glaciation.
The Toba Catastrophe Theory also explains the large apparent variation of humans despite our relatively low genetic diversity. Ambrose believes humans survived the bottleneck in several isolated, uncrossed pockets. Tropical refuges in Africa are said to be the few places where humans have survived. The total number of breeding pairs on Earth would never exceed 10,000 for a millennium-long period. After the 1000 years, continued migrations would have rapidly brought nesting populations back into contact, preventing them from drifting into distinct species.
The Toba Catastrophe Theory has been met with a mixed response from the scientific community. In general, it seems that evidence is accumulating on his side. Since there would have been limited artifacts left over from such small populations, our only hope for more knowledge is genetic and climatic studies.
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