One of the most popular posts here is Tim Jones’ post, published almost 11 years ago on the Toba Eruption. Toba Catastrophe Theory was proposed first by Stanley Ambrose. Henry Harpending popularized it. In a nutshell, a genetic bottleneck has been observed in Homo sapiens occurring approx. 70,000 years ago that temporally correlated with a massive eruption of a volcano whose caldera is now Lake Toba in Sumatra.
Toba is thought to be the greatest known volcano to erupt. It is believed to have been 19 times more powerful than Mt. St. Helens. The ash that covered the skies is thought to have made the world 7 degrees colder. Over 90% of humans at the time are thought to have died, leading to a bottleneck of only 10,000 or so people to survive.
Last week’s Nature published a paper looking at two human sites located in the tip of South Africa, and ultimately debunks the claim. One site, an open campsite (Vleesbaai Area B (VBB)) and another more sheltered alcove (Pinnacle Point Site 5-6 (PP5-6)) housed humans during the Toba eruption. Looking at each strata of earth and analyzing exactly what these humans trashed before, during and after the catastrophic eruption the researchers were able to see a representation on human activity. The eruption of Toba left a signature layer of sediment that correlated with other known Toba sediment deposits.
Curiously, the group saw that these people who survived the eruption left behind more trash after the eruption than before it. That is counterintuitive. Putting aside the assumption that sites like this would be demolished during a catastrophic volcanic winter. But the contrary happened at VBB and PP5-6. Instead, these sites grew, they ate more, they invented new tools… The archaeological record at these sites prevaled despite the eruption.
It is possible these places were a refuge. But that also doesn’t correlate to any other animal, plant or other hominin bottlenecks of the same time. We know other animals and plants thrived, so why didn’t 90% of other species die?
So what exactly, caused the genetic population bottleneck? Founder effect, possibly. As humans migrated, they became less dense. Smaller groups with less diversity entered Eurasia, and that became more pronounced as they wandered farther East. Those who remained in Africa remained more diverse.