How Human Beings Almost Vanished From Earth In 70,000 B.C.

Toba catastrophe theory

The Toba catastrophe theory suggests that a bottleneck of the human population occurred c. 70,000 years ago, proposing that the human population was reduced to perhaps 10,000 individuals^[3] when the Toba supervolcano in Indonesia erupted and triggered a major environmental change. The theory is based on geological evidences of sudden climate change and on coalescence evidences of some genes (including mitochondrial DNA, Y-chromosome and some nuclear genes)^[4] and the relatively low level of genetic variation with humans.^[3]
However, such coalescence is genetically expected and does not, in itself, indicate a population bottleneck, because mitochondrial DNA and Y-chromosome DNA are only a small part of the entire genome, and are atypical in that they are inherited exclusively through the mother or through the father, respectively. Genetic material inherited exclusively from either father or mother can be traced back in time via either matrilineal or patrilineal ancestry.^[5] Research on many genes finds different coalescence points from 2 million years ago to 60,000 years ago when different genes are considered, thus disproving the existence of more recent extreme bottlenecks (i.e., a single breeding pair).^[3][6]
On the other hand, in 2000, a Molecular Biology and Evolution paper suggested a transplanting model or a 'long bottleneck' to account for the limited genetic variation, rather than a catastrophic environmental change.^[7] This would be consistent with suggestions that in sub-Saharan Africa numbers could have dropped at times as low as 2,000, for perhaps as long as 100,000 years, before numbers began to expand again in the Late Stone Age.^[8]