I've been reading on the Toba Catastrophe theory and that it supposedly caused a genetic bottleneck in humans some 70k years ago, which raised a question that I couldn't find an answer to by searching the internet.
According to wikipedia:
It is supported by genetic evidence suggesting that today's humans are descended from a very small population of between 1,000 and 10,000 breeding pairs that existed about 70,000 years ago
My question is regarding this evidence.
Is it a case of simply observing expansion of genetic diversity form a projected point of low genetic diversity and pinning it on the event that is most likely to have caused it?
Or is there genetic evidence, obtained from sequencing DNA from humans from say 80k and 60k years ago that proves genetic diversity 80k years ago was indeed higher and abruptly dropped due to that exact catastrophic event?
The former seems kinda possible, because as severe as the eruption might have been, most of the people back then were in Africa, which is on the other side of the planet, and the estimated global impact doesn't seem to be anywhere nearly as severe as to cause the extinction of a substantial amount of the human population.
I think the human, as a more intelligent omnivore, should be somewhat more resilient to such catastrophes than any large herbivore or apex predator. Yet there is no information on such species being largely affected by that event, although there are a few species that appear have been affected.
Furthermore, there appears to be evidence that human populations were not completely extinct even in areas as close as southern India.
Last but not least:
genetic analysis of Alu sequences across the entire human genome has shown that the effective human population size was less than 26,000 at 1.2 million years ago; possible explanations for the low population size of human ancestors may include repeated population bottlenecks or periodic replacement events from competing Homo subspecies
A study by Chad Yost and colleagues of cores from Lake Malawi dating to the period of the Toba supereruption showed no evidence of a volcanic winter, and they argue that there was no effect on African humans. In the view of John Hawks, the study confirms evidence from a variety of studies that the eruption did not have a major climatic effect or any effect on human numbers
Which further goes to add substance to my suspicion that the Toba event, as unlikely as it may be as a cause, was simply picked as the most convenient / least unlikely candidate.
So, in short:
Is it known for an evidence supported fact that this particular eruption caused an abrupt drop in genetic diversity and a genetic bottleneck, and if so, reference to said evidence will be appreciated, or is it merely the most plausible candidate to explain an observable genetic diversity expansion from a projected fairly recent initial condition of low genetic diversity?
Or to put it even shorter, is there evidence that humans were more genetically diverse prior to said event?