The doubt about the Toba genetic bottleneck theory surrounds the notion that Toba caused it, not around whether the bottleneck existed. The notion that all of us alive today can trace our ancestery to just a few thousand individuals at aorund the time of eruption of the youngest Toba tuff is well attested genetically. The question about the link to Toba arose from the fact that if an volcano erupting half a world away could kill most humans alive, then it must have also been powerful enough to create very widespread genetic bottlenecks in all sort of species everywhere in the world. We don't see strong evidence of widespread havoc around the world, only primates in Africa seem to suffer this bottleneck. This suggests whatever created the bottleneck was local to Africa.
But this is only a suggestion. Massive volcanic eruptions can create very powerful indirect effects that would devastate populations a great distance away while sparing nearby populations. For example, by far the greatest volcanically induced casualty ever inflicted on mankind in recorded history occurred in in 1780s in Africa, near where we think HS were when Toba erupted. At least 2 million Egyptians starved to death. The cause of the diseater? An volcanic eruption in Iceland. There were no similar population diseasters anywhere else in the world during that time. We know through numerous weather observations and records that the volcanic eruption in Iceland ejected aerosol into the upper atmosphere that changed the global weather pattern, causing the following year's monsoon to fail, leading to collapse of agriculture in Egypt, and the massive femine. But if all we had were grave records, we would be perplexed how it it could be that a volcano in Iceland could kill so many in far away Egypt while leaving the rest of the world nearly untouched.
But this is only a suggestion. Massive volcanic eruptions can create very powerful indirect effects that would devastate populations a great distance away while sparing nearby populations. For example, by far the greatest volcanically induced casualty ever inflicted on mankind in recorded history occurred in in 1780s in Africa, near where we think HS were when Toba erupted. At least 2 million Egyptians starved to death. The cause of the diseater? An volcanic eruption in Iceland. There were no similar population diseasters anywhere else in the world during that time. We know through numerous weather observations and records that the volcanic eruption in Iceland ejected aerosol into the upper atmosphere that changed the global weather pattern, causing the following year's monsoon to fail, leading to collapse of agriculture in Egypt, and the massive femine. But if all we had were grave records, we would be perplexed how it it could be that a volcano in Iceland could kill so many in far away Egypt while leaving the rest of the world nearly untouched.
