Our species almost didn't make it.
Population reduced to less than 10,000.
While recently studying animal extinction in New Zealand, I fell across a series of articles showing how close the human race came to dying out.
Around 70,000 years ago, humanity's global population dropped to between 3,000 and 10,000 individuals, and this had major effects on the human species.
When looking for reasons why the sudden reduction in population, a theory emerged that a massive super-volcano (in Indonesia) erupted,
blackening the sky with ash, plunging earth into an ice age, and killing off all but the hardiest humans.
eruption, occurred 70,000 years ago. It pushed 2,800 cubic Kilometers of dust and ash into the air.
Measuring the debris blown into the air in "Cubic Kilometers".
* Toba pushed 2,800 cubic KM - Taupo 50 cubic KM - and - Mt St Helens 1 cubic KM
When Toba erupted the debris settled to an ash layer that was 6cm thick across South Asia, the Indian Ocean, the Arabian and South China Sea.
Research from the late 1990s and early 2000s suggested that this eruption, on Sumatra in Indonesia, blocked the sun across much of Asia, causing a harsh volcanic winter
and a 1,000-year-long cooling period on earth. Not too difficult to imagine a resultant population decline.
The Toba super-volcano eruption was a convenient answer to the near doom written in our DNA.
But recent archaeological evidence shows that human hunter-gatherer settlements in India weren't too affected by the eruption and quickly recovered. Temperature data embedded
in the geology of Lake Malawi, in East Africa, also suggests that the region didn't cool off that drastically.
Scientists, generally, now disagree on the idea that the Toba eruption caused this near extinction event, however 'something' occurred (measured by geneticists) that reduced
our population so dangerously close to our end.
This populatin reduction resulted in more pressure on our ancestors and caused what's known as a 'genetic bottleneck', which decreases the genetic variation in a population.
Smaller populations with reduced genetic variations, become more susceptible to disease and environmental disasters, and certain genetic traits (negative and postive) can incrementally accumulate.
Bottlenecks also slow evolutionary change, since fewer members of the species are around to pick up genetic mutations.
Genetic bottlenecks can also cause an effect where small, isolated populations can drastically diverge from the original population.
As humans spread across the planet, scientists believe that our population experienced multiple bottlenecks and, as a result, a serial-founder effect kicked in to create the types of
diversity we currently see in the human race today. Scientists have mapped these events to geographic choke points around the world, based on decreasing genetic diversity as we migrated.
It's also why, when you compare humans to other species, human DNA is not very diverse when you consider our globe-spanning range.
So what did cause that major bottleneck 70,000 years ago, if not a giant volcano and an ice age?
Scientists aren't sure, but they have some new ideas. A catastrophic spread of disease, for example, may have played a role. Or perhaps the way we currently model the movement of humans dispersed out of Africa needs some adjustment.
Whatever the case, now is as good a time as any to thank your 70,000-year-old ancestors for surviving this perilous time in human history.
We almost didnt make it, but 40,000 years ago the population rose to just under 1 Million. By 1804 we grew to 1 the Billion mark,
and 3 Billion by 1960 and is 7.9 Billion right now, and a projection of 9.5 Billion by 2050 seems to be the acepted norm right now. - - (Check www.worldometers.info for a representation of population growth.)
David Quammen's book "Spillover: Animal Infections and the Next Human Pandemic"
is about people pushing into forests, swamps and places where viruses have been hiding. Those viruses are now beginning to cross
over into horses, pigs, bats, birds and, inevitably, they threaten to "spillover" into us.
For a virus, or bacteria, 8 billion potential hosts look like a fantastic opportunity.
This is well written, and even though 10 years old it 'reasonates' with regard to Covid-19.
"What might the next big one be?".....