74 thousand years ago, a big chunk of the island of Sumatra blew up. It was the biggest volcanic explosion in the past two million years, expelling 2800 times as much debris as the Mount Saint Helens eruption in Washington State in 1980. Ash from the super-eruption is found all the way from Lake Malawi to the South China Sea. The resulting Toba caldera measures about 20 by 60 miles.
The Toba eruption coincides with a shift back to glacial conditions, and it has been argued that there’s a connection, that Earth went through a long volcanic winter after the eruption, which shifted climate to a colder equilibrium.
Did Toba have an effect on human evolution? Somewhere between 100 and 50 thousand years ago, human populations went through a bottleneck: modern humans are descended from just 1,000 to 10,000 breeding pairs from that period. It’s been argued that Toba wiped out the majority of Homo sapiens around at the time, leaving only a small group of survivors.
But the evidence that Toba is responsible for the bottleneck is equivocal. In some places humans seem to have passed through the period of the eruption without major disruptions. Also, there’s a point that gets missed in a lot of popular reporting: just because a species goes through a bottleneck doesn’t necessarily mean that the population of the whole species ever shrank to that size. In the case of Homo sapiens it could be that the total population was always many times larger than 10,000. It’s just that the others tens or hundreds of thousands got replaced. In other words, we may not be looking at an external catastrophe wiping out most of humanity, and a few groups of survivors recovering. Instead, we may be looking at a small population of our eventual ancestors expanding and outcompeting other populations, so that it was our ancestors, not a volcano, who made sure that most human beings alive 70,000 years ago didn’t leave descendants. We will see later on in Logarithmic History that population replacements have been a common occurrence in human history.
In May 2015, the Toba volcano grew more active than usual, producing large emissions of steam and foul gases. Locals were reported to be concerned.