Our mitochondrial DNA shows that about 70,000 years ago, due to nuclear winter, human extinction was on the verge from the Earth. The population had declined to about 10,000 individuals. Scientists found traces of humans extinction events in the genomes of East African chimpanzees, South Asian tigers, and orangutans. So, at that time, there was a tremendous natural disaster that destroyed many species and actually formed a modern human.
Bottleneck and gene drift
In 1993, an international team of scientists first analyzed human mitochondrial DNA and found traces of two important processes – a bottleneck and gene drift. A bottleneck indicates the sharp reduction in the population and the depletion of the gene pool – many gene variants simply disappear along with their not very successful carriers.
A gene drift is characteristic of small populations, where the frequency of occurrence of a particular variant of a gene changes quickly and completely randomly. Any demographic event, say, the sudden death of only one adult childless man, can permanently change the color of the eyes or hair of future members of his tribe.
Interpretation of these data is unequivocal: 50,000-70,000 years ago, humanity was on the verge of extinction. The population dropped sharply to 10,000 and has been remaining small for quite a long time.
“Forty? Come on, that can’t be right. Well, the technical term is 40 “breeding pairs” (children not included).” “More likely there was a drastic dip and then 5,000 to 10,000 bedraggled Homo sapiens struggled together in pitiful little clumps hunting and gathering for thousands of years until, in the late Stone Age, we humans began to recover.” But for a time there, said science writer Sam Kean, “We damn near went extinct.”
Four years later, traces of the same processes were found in the genome of East African chimpanzees. The genetic diversity of mitochondrial DNA in monkeys was as low as in humans. In 2004, when deciphering the genome of South African tigers, researchers obtained very similar data. And then, signs of a bottleneck and gene drift were found in the DNA of orangutans living in Sumatra and Borneo. Everything suggests that in the distant past, animals, together with our ancestors, survived a global natural disaster.
Long volcanic winter: Human Ancestors Were an Endangered Species
On Earth, there are twenty supervolcanoes, whose eruptions can cause climate change on the planet. Swiss scientists found out that those volcanoes wake up once in a hundred thousand years, and the last eruption happened about 75,000 years ago, just before a human bottleneck. This is the Indonesian volcano Toba.
As a result, the huge Toba lake arose on Sumatra, volcanic ash deposits formed on the territory of almost 40 million square kilometers.
The ash is at the bottom of the African Lake Malawi, seven thousand kilometers from Sumatra, and a sharp jump in the content of salts of sulfuric acid recorded in ice cores from Greenland also occurred during this period, 74,000 years ago.
There was so much ash that, once in the atmosphere, it blocked the sunlight for several months, and a volcanic winter came. This information was suggested by an international team of researchers.
The climate did not indulge our ancestors anyway, as that was the last ice age. After the eruption of Toba, the average annual temperatures reached a minimum, falling, according to various sources, by 5-15 degrees Celsius.
Was there a disaster?
It all explains why the first Homo Sapiens, who left Africa 125,000 years ago, completely died out, and the number of those who remained in their native continent was reduced to a critical ten thousand individuals.
However, there is evidence contrary to the hypothesis of the great and terrible Toba. In excavations in southern India, American anthropologists have found Paleolithic tools both below and above a layer of volcanic ash.
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The situation is similar to the sites of ancient people on the coast of South Africa. The guns found there indicate that our ancestors had settled in those places before, during, and after the disaster. There was no interruption in archaeological cultures that were synchronous to the eruption of a supervolcano. Moreover, it was as if the disaster had bypassed Neanderthals, who, after awakening Toba, reached their peak, albeit briefly.
After examining that Tobian ash raised from the bottom of Lake Malawi, scientists concluded that its concentration is insufficient for a serious impact on the local ecosystem. If there were a lot of ashes, and the temperature in the region dropped by at least four degrees, a significant part of the biota would have died in the upper layers of the lake. But, judging by the sediments, nothing like this happened.
Consequently, the eruption of Toba and the alleged volcanic winter could not cause a bottleneck through which humanity passed. However, researchers have no doubt about the fact that our ancestors nearly died out about 70 thousand years ago. On Earth, a global natural disaster really happened.