In the study of population bottlenecks, there is one which stands out above all others and has been a source of endless speculation since it was discovered. Through science, we have a couple of dates, one a vague range of when modern man left the shores of Africa and another, a more definitive date of when the Toba supervolcano erupted - 73,000 years (± 4,000 years ago. Click on the link above to follow up on the definitive site that shares the best details about this global catastrophe that affected all mankind.
The Toba eruption deposited a 15-cm thick ash layer over the entire South Asia and large swathes of the Indian Ocean range, its range extending to about 2800-km radius, followed by a sudden volcanic winter that resulted in sunlight being blocked and rapid deforestation, in turn causing the major devastation to flora, fauna – and man.
It was estimated that the Toba eruption reduced the population to perhaps between 1,000 to 10,000 breeding pairs of humans worldwide, thus creating a population bottleneck. Oppenheimer even suggests that it caused mass extinctions of early human settlers in the subcontinent, but that man had already moved beyond the subcontinent to (at the very least) South East Asia by that point in time.
Herein lies the conundrum – did modern man actually reach the shores of South East Asia by this time – or are these dates questionable? Did the Toba disaster really have a profound effect leading to near complete repopulation of South Asia, or was the disaster profound, but left the subcontinent with a population foothold? It has been a question that has puzzled me for a long time and this is the topic which I attempt to cover within the context of this article and the next.
What happened after the Big Bang?
Firstly, its best to start off with a map, showing the extent of the Toba ash fall. For this, I would like to propose a great starting point in George Weber’s Lonely Island site, which discusses the Toba supervolcano in detail; as the map below shows, the range of the devastation was vast, but the range of significant, immediate fallout was defined and rather specific. There is, however, evidence of pyroclastic ash fall of an average of 10cm over the entire surface of the earth.
The red numbers indicate where ash was found on land, the blue numbers indicate where is was found at the bottom of the sea. The thick red lines indicate where the pumice must have washed up onto the shores and the thin red line indicates where the possible extent of the fallout.
Thus far, we have established a couple of fairly indisputable facts; one, that man did push out of Africa around 90 to 80 kya; secondly, only a single, relatively small wave of homo sapiens sapiens pushed out, all carrying the mtDNA haplotype L3, which then diversified into the M and N types (and subsequent haplotypes). Thirdly, the Toba eruption did take place around 74000 years ago, give or take a couple of years.
Finally, the evidence that we have may suggest that modern man had by then reached the shores of Kota Tampan in modern day Malaysia, based around corroborative evidence.
But who could have survived such a catastrophe? Was this the only such catastrophe in existence? Was the survival uniform and did it also indicate in turn a back-migration to repopulate the subcontinent of India, which was directly in the wake of the eruption?
The next article covers the details of what happened next…