Book: When Humans Nearly Vanished

A brand new book on an old theory, a supervolcano erupted in Sumatra 74,000 years ago (±400ya) and reduced the human population to as few as 1,000 breeding pairs worldwide.

Not only our own genetics support such an hourglassing, but the genetics of the bacteria in our gut Heliobacter pylori, the genes of the strain of lice unique to humans, and several other indicators.

Wikipedia wrote:

Parallel bottlenecks were proposed to exist among chimpanzees, gorillas, rhesus macaques, orangutans and tigers.[9] The hypothesis was based on geological evidence of sudden climate change and on coalescence evidence of some genes (including mitochondrial DNA, Y-chromosome DNA and some nuclear genes)[10] and the relatively low level of genetic variation in humans.

The layer of ash and high concentration of sulfuric acid in deep sea cores and glacier cores dated to 74,000 years ago all point to a volcanic event. The chemistry of this ash layer matches the chemistry of the Toba volcano in Sumatra.

This was well before the Neanderthals died out (~40,000 ya) and after modern humans migrated out of Africa but coincides with the Southern Dispersal theory. The likely interbreeding with Neanderthals and Denisovans also dates to this period.

The facts supporting this theory are few and simple. The author has therefore filled out the book with a lot of history of supervolcanos, genetics theory and science history. Meanwhile, other explanations remain popular.

Wikipedia wrote:

However, subsequent research, especially in the 2010s, appeared to refute both the climate argument and the genetic argument. Recent research shows the extent of climate change was much smaller than believed by proponents of the theory.[11] In addition, coalescence times for Y-chromosomal and mitochondrial DNA have been revised to well above 100,000 years since 2011. Finally, such coalescence would 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.[citation needed] Genetic material inherited exclusively from either father or mother can be traced back in time via either matrilineal or patrilineal ancestry.[12]

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.[6] 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.

Homo erectus first appeared in Africa 1.9 million years ago, and doesn’t disappear from the fossil record until 70,000 years ago — making it the longest lasting hominid species, and thus perhaps the most successful.

Individuals reached six feet in height, brain sizes at 1000cc were only slightly less than sapiens 1250, erectus used fire and built shelters of rock and wood. sapiens evolved out of erectus approximately 315,000 years ago.

Neanderthals lived from 450,000 to 40,000 years ago.

Denisovians lived from about 600,000 to 41,000 years ago. Modern Aborigines share about 3-5% Denisovian DNA.

Therefore, for the period 315,000 to 70,000 years ago there were at least four separate species of mankind living simultaneously. The theory that women are a separate species from men has yet to be scientifically validated, although apocryphal evidence abounds.

Aborigines are not the only ones with Denisovan DNA. I have about 0.7%.

Adam Rutherford wrote:

We can see, almost certainly, that language is [not as old as full modernity in our brains and voice boxes.] Our brains are not significantly different from when we first started dabbling in art, and indeed don't seem fundamentally different from Neanderthals. The [physiology] of modernity has been with us for tens of thousands of years before it's arrival. If Paleolithic people were biologically similar [to us], the question is this: why did it take so long to become modern when we were physically ready for thousands of years?

I suspect, without any evidence, that the genesis of language dates to the great hourglassing of the human population 74,000 years ago when the H. sapiens race almost went extinct. The survivors were forced into a cleverness not previously required. They interbred with Neanderthals and Denisovians, and may have learned language from them. They needed to communicate to survive, indeed may have used language to wipe out their Homo competition. The great diaspora across all the continents soon followed, bringing not only genetically identical people but shared art and ritual and thus probably(?) language.