The Toba Catastrophe
Dave Price
Is this why humans have relatively little genetic variance compared to most species?
Geneticists Lynn Jorde and Henry Harpending of the University of Utah proposed that the variation in human DNA is minute compared to that of other species. They also propose that during the Late Pleistocene, the human population was reduced to a small number of breeding pairs — no more than 10,000 and possibly as few as 1,000 — resulting in a very small residual gene pool. Various reasons for this hypothetical bottleneck have been postulated, one of those is the Toba catastrophe theory.When I read theories like this, it always brings to mind the Drake equation and the weak anthropic principle, and makes me wonder just how incredibly unlikely a chain of coincidences we rode on the path to intelligence.
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According to the Toba catastrophe theory, 70,000 to 75,000 years ago a supervolcanic event at Lake Toba... The theory was proposed in 1998 by Stanley H. Ambrose of the University of Illinois at Urbana-Champaign.
Within the last three to five million years, after human and other ape lineages diverged from the hominid stem-line, the human line produced a variety of species.
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According to the Toba catastrophe theory, a massive volcanic eruption severely reduced the human population. This may have occurred around 70–75,000 years ago when the Toba caldera in Indonesia underwent an eruption of category 8 (or "mega-colossal") on the Volcanic Explosivity Index. This released energy equivalent to about one gigaton of TNT, which is three thousand times greater than the 1980 eruption of Mount St. Helens. According to Ambrose, this reduced the average global temperature by 5 degrees Celsius for several years and may have triggered an ice age.
Interestingly, the authors think that microbrial life should be relatively common, but that getting beyond that point for any significant period may be virtually impossible (lone exception being present company, of course).
The weak anthropic principle is pretty frightening when you really think about it. It says that everything, no matter how unlikely, required to happen in order for intelligent life to exist has to have happened, because we are in fact here -- but makes zero guarantees we will survive even another minute.
I've read of the Toba hypothesis a few years ago, and it makes a lot of sense. One part that the scientists, at least the anthropologists are afraid to talk about is how it affects the "out of africa" theory.
The OOF theory assumes that all current humans descended from a single source in Africa based upon mitochondrial DNA results and comparisons. However, if the human near-extinction due to Toba's eruption is correct, it may well indicate that the survivors on earth are related through being descended from that one bloodline, NOT that all humans came from it. Serious consequences there.
The problem with current human-development theories is that they depend purely upon discovered data, much of it, imho quite over-analysed and with too much extrapolation, and they automatically ignore any other possibilities out of hand, based upon lack of physical evidence.
Just because physical specimens do not exist currently doesn't mean they don't, well, exist. It may well mean that we simply haven't found them yet.
Anyway, it's nice to see others interested in the Toba event. If you want a similarly frightening scenario that may be in our near future, then read up on the super-volcano that is Yellowstone Park.
Sobering. We really need to be a space faring civilization.
I have two interpretations of the Great flood. One - for a while humanity lived on the big river valleys and rivers flood. Two, rising water levels from the end of the ice age, possibly the Black Sea deluge.
As I seem to be in a a book recommending mood, I also enjoyed Before the Dawn by Wade. It postulated waves of migration out of Africa (ok postulated is probably too strong as Wade is a pop-sci writer for the NYT and is mostly repackaging/synthesizing others' hypotheses, but you get the point). It's very good at synthesizing antrhopology with genetics. I would be interested in hearing Tim's thoughts on it if he's read it.
I haven't read "Before the Dawn" but I'll certainly get hold of a copy in the near future.
My whole interest in this subject comes from the point of an amateur archeologist and historian. I always question hypothoses, as we all should, because there have been times when certain conclusions were drawn based upon a single point of data, or a very small sample, and then presented to the world as established fact. this in turn led others to discard alternative explanations that miht have been a better example.
Here's one small example. Historians researching the American Civil War have for years accepted as fact that bayonets were rarely used in combat, and much ink has been expended in all sorts of tactical journals and dissertaions about ACW tactics where the bayonet was eliminated from discussion.
This comes from an examination of the Surgeon General's reports to Congress after the war. In compiling his report, the SG listed many tables showing types of wounds treated, diseases, etc. He noted that fewer than 1000 bayonet wounds were treated in Union Army Hospitals. Historians used that fact as the basis for their claims.
How then to square that figure with the many accounts of how "we pitched into the enemy with clubbed muskets and bayonets" reports from the field of "bayonet charges", etc. The answer was simple. Bayonet wounds are almost always fatal or so slight that they were treated on the field and the soldier went back to duty. Those bayonet wounds listed by th SG were those serious enough to require treatment in hospital, and nothing more.
Historians failed to examine other data sets, took a simple fact which supported their pre-conceived beliefs, disregarded other sources, and ran with it. As a result many history books have this error which is compounded by repeat printings of it by other authors, thus it gets the mantle of proven fact.
I think the same might well be said of the "out of Africa" theory. It might well be true, insofar as it represents the survivors of the Toba event. Yet, what about all the tens of thousands of humans elsewhere upon the globe? We might have lost their remains due to the Toba event, We don't know.
Anyway, it's a facinating subject, and one that's fun to speculate upon.
Of course we all lose our tempers now and then. Dean freely admits to being imperfect in this regard, which is why regulars to this establishment will generally be cut more slack than people who we don't know very well.
Still: behave like an adult, or go find somewhere else to play. Thanks.