Ambrose was also the first to suggest that Toba could have been responsible for human differentiation, so for him as well as Oppenheimer, it would have been a kind of "Cosmic Inflation" type thing. However, if all humans were confined to Africa when Toba hit, it's impossible to see how any differences produced by that event could have evolved into the worldwide distinctions so evident today, of which Africa is a relatively homogeneous part. Toba can explain the large-scale distributions we now see only if humans had already left Africa and had occupied most or all of the south Asiatic coast by the time it erupted. However, Ambrose, for reasons that continue to puzzle me, insists that this is not possible and that all the archaeological evidence points to an African exodus after the Toba eruption, not before (personal communication).
It was only Stephen Oppenheimer, apparently, who saw the necessity of the Out of Africa migration preceding the Toba event, because otherwise it could not have had the necessary effect. And in this sense it's possible to turn things around, so that instead of timing the great migration on the basis of (shaky and incomplete) archaeological assumptions, we can use the timing of the Toba eruption itself to much more precisely estimate the date of the fateful exodus, which would have to have preceded it by at least a thousand years or so.
Currently, most archaeologists and geneticists seem to agree, based on certain fossil finds in Australia, as well as estimates of genetic "coalescence," that the most likely date for the great migration is somewhere between 60,000 and 50,000 years ago, thousands of years after Toba. And on that basis, Toba has been discounted as a factor in human evolution. For many, the last nail in the coffin was provided by archaeologist Michael Petraglia, who, after years of digging and probing, found some very interesting stone tools both below and above Toba ash (Middle Paleolithic Assemblages from the Indian Subcontinent Before and After the Toba Super-Eruption, Petraglia et al, 2007).
In a blog post entitled At Last, the death of the Toba bottleneck, paleoanthropologist and long time Toba skeptic John Hawks gleefully reported the findings thus: "This week's paper by Petraglia and colleagues (2007) appears to have sunk the Toba bottleneck entirely. Very simply, they found a Toba ash horizon in India, and found very similar archaeology both below and above the eruption."
Petraglia's results were widely reported in the media in much the same terms, as though the mere fact that more or less the same type of tools were found above as below the ash meant that the effects of the Toba eruption could be discounted. Thus Hawks concluded: "In the meantime, we can forget about the cataclysmic effect of Toba on the poor hominids."
What was all but ignored in such reports was a far more significant finding:
these pre- and post-Toba industries suggest closer affinities to African Middle Stone Age traditions (such as Howieson's Poort) than to contemporaneous Eurasian Middle Paleolithic ones that are typically based on discoidal and Levallois techniques. . . This interpretation would be consistent with a southern route of dispersal of modern humans from the Horn of Africa (24); the latter, however, will remain speculative until other Middle Paleolithic sites in the Indian subcontinent and Arabian Peninsula are excavated and dated (my emphasis).
In other words, what Petraglia found that went almost unnoticed was evidence that the Out of Africa migrants may have been in southern India at the time of the Toba eruption after all. This was a finding of major importance, the first archaeological evidence consistent with the presence of modern humans in Asia at such an early date, but it got lost in all the hoopla surrounding the apparent debunking of the Toba "myth."
Petraglia may have had second thoughts, as he went out of his way to clarify the meaning of his results in a subsequent interview (Modern Humans Lived in India Earlier Than Thought, Study Finds, by Chris Dolmetsch, Bloomberg):
"This is some of the earliest evidence for the spread of modern humans out of Africa towards Australia,'' Petraglia said in a telephone interview from New York.Oh and by the way, the artifacts in question were found "under a 2.5 meter (8.4-foot) thick ash deposit . . . " If anyone really believes the effects of an accumulation of over 8 feet of ash on human survival can be discounted, I hear that John Hawks has a bridge over in Brooklyn he can sell you real cheap. (No offense, John. :-) )The study says the relics, made of limestone, quartzite, chert and other minerals, are likely from a variety of stone tools from the Indian Middle Paleolithic era that lasted from about 150,000 to 38,000 B.C.
Yet the characteristics of the artifacts are more typical of the African Middle Stone Age that ended about 40,000 years ago than they are of younger artifacts found elsewhere in Europe and Asia, the study says. That finding suggests that modern humans had migrated out of Africa and were already in southern India when the Toba Tuff eruption blanketed the region in ash.
"It will be very much debated," Petraglia said. "There are people that are wedded to their theories and won't like it at all, and there are others who will welcome our study because this part of the world is very understudied."
In another interview (National Geographic) Petraglia makes clear that his results do not mean Toba was a piece of cake:
"The fact that we have this ash is just icing on the cake, because it tells us that if it's modern humans, then they were able to persist through a major eruptive event," he said. "But they would have had a very, very difficult time."What Petraglia's findings suggest to me is that the Toba blast was not sufficient to have had much of an effect on Africa, as Ambrose has argued, or Europe either -- but it would certainly have had a very significant effect on any modern humans living in South Asia, and could certainly have had lasting consequences for human history.
(to be continued . . . )
"What was all but ignored in such reports was a far more significant finding:
ReplyDeletethese pre- and post-Toba industries suggest closer affinities to African Middle Stone Age traditions (such as Howieson's Poort) than to contemporaneous Eurasian Middle Paleolithic ones that are typically based on discoidal and Levallois techniques. . . This interpretation would be consistent with a southern route of dispersal of modern humans from the Horn of Africa (24); the latter, however, will remain speculative until other Middle Paleolithic sites in the Indian subcontinent and Arabian Peninsula are excavated and dated (my emphasis)."
I interpret it as a migration of "AMH" out of Africa before the Toba eruption, followed by a migration of Homo sapiens sapiens into South Asia from East Asia, Southeast Asia or South Siberia after the Toba eruption. It means there's no genetic continuity between pre-Toba and post-Toba occupants of South India. Since Australian Mungo man was re-dated to 40K, there's no evidence that Australia had been peopled prior to that. Otherwise, one could argue that the "southern route" was the one "AMH," which, IMO, don't have anything to do with Homo sapiens sapiens, took out of Africa all the way to Australia. Most likely, the migration of AMH out of Africa was stopped by Toba in South India. However, this has nothing to do with Homo sapiens sapiens who are entirely unaffected by Toba, which is the present-day consensus.