When the volcano blows

Nobel Prize-winning physicist Richard Feynman once said, "I would rather have questions that cannot be answered than answers that cannot be questioned."

The strength of science is in its ability to self-correct, but this does engender a problem; it may well be that some of the questions we're asking will never be satisfactorily answered.  There are sometimes when we must admit ignorance, and hold our determination to have everything figured out in abeyance -- possibly indefinitely.

That may be the situation we're in with regards to an interesting question surrounding the largest volcanic eruption in modern times, the eruption of Toba in the Indonesian archipelago.  This eruption dwarfed Mount Saint Helens, the 1883 eruption of Krakatoa, and even the catastrophic eruption of Tambora (also in Indonesia) in 1815, that threw so much in the way of debris up into the atmosphere that it caused the "Year Without a Summer," in which Quebec City got a foot of snow -- in mid-July.

The Toba eruption, 74,000 years ago, was bigger than all of the above; by some estimates, it threw a hundred times more in the way of pulverized rock into the air than Tambora did.  It is certain that it caused not only localized devastation, but worldwide climate change.  And the conventional wisdom is that it nearly wiped out the human species -- that we were driven into a genetic bottleneck, in which only a few survivors became the ancestors of everyone currently alive today.

The Toba caldera [image courtesy of the Wikimedia Commons]

Michael Rampino and Stanley Ambrose, of New York University, were amongst the first proponents of the Toba bottleneck theory.  In their paper "Volcanic Winter in the Garden of Eden: The Toba Supereruption and the Late Pleistocene Human Population Crash," published in 2000 in the Papers of the Geological Society of America, they write:

Genetic studies indicate that sometime prior to ca. 60,000 yr ago humans suffered a severe population bottleneck (possibly only 3,000-10,000 individuals), followed eventually by rapid population increase, technological innovations, and migrations.  The climatic effects of the paroxysmal Toba eruption could have caused the bottleneck, and the event might have been a catalyst for the technological innovations and migrations that followed.  The present results as to the predicted environmental and ecological effects of the eruption lend support to a possible connection between the Toba event and the human population bottleneck, and suggest that similar bottlenecks among other organisms might be expected at about the same time. 

However, it appears that the question is far from settled.  A paper by Eugene Smith et al. that came out last week in Nature, "Humans Thrived in South Africa Through the Toba Eruption about 74,000 Years Ago," completely counters the conventional wisdom -- and suggests that if the bottleneck did occur, it may not have been the fault of the volcano:

Approximately 74 thousand years ago (ka), the Toba caldera erupted in Sumatra.  Since the magnitude of this eruption was first established, its effects on climate, environment and humans have been debated.  Here we describe the discovery of microscopic glass shards characteristic of the Youngest Toba Tuff—ashfall from the Toba eruption—in two archaeological sites on the south coast of South Africa, a region in which there is evidence for early human behavioural complexity.  An independently derived dating model supports a date of approximately 74 ka for the sediments containing the Youngest Toba Tuff glass shards.  By defining the input of shards at both sites, which are located nine kilometres apart, we are able to establish a close temporal correlation between them.  Our high-resolution excavation and sampling technique enable exact comparisons between the input of Youngest Toba Tuff glass shards and the evidence for human occupation.  Humans in this region thrived through the Toba event and the ensuing full glacial conditions, perhaps as a combined result of the uniquely rich resource base of the region and fully evolved modern human adaptation.

The reason I bring this up -- besides the fact that I'm interested in human population genetics, and it's cool -- is that this may be a question that we simply don't have the data to answer.  It's possible that the "thriving" population that Smith et al. found was a localized group of lucky people, and elsewhere, humanity got clobbered.  On the other hand, it could be that the Rampino and Ambrose paper was simply wrong -- that the population genetics studies, which are not without their a priori assumptions, overestimated the extent of the Toba bottleneck (or the whatever-caused-it bottleneck).

But -- and this is the most critical point -- you keep looking.  If there's no definitive solution, you are forced to admit it, but the research doesn't stop there.  Ignorance is the beginning, not the end, of the scientific process.

So we may never know exactly how close humanity came to extinction 74,000 years ago.  The important thing is that we've asked the question -- and that science gives us a means to evaluate the evidence, and determine if a particular answer is supported.  And what we learn along the way will open up further avenues for exploration, enough to keep the scientific world occupied for a long, long time.

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All in the family

Racists have cast about for years for some sort of scientific basis for their horrible worldview.  Evidence that their race is the superior one in intelligence, physical strength, or vigor, or simply support for their contention that interracial marriages are bad in a biological sense.

Of course, the problem for people who turn to science is that science often provides answers whether you end up liking them or not.  And inquiries into a biological basis for race have shown that any real genetic variations between different ethnic groups are tenuous at best.  Luigi Luca Cavalli-Sforza, one of the leading specialists in human population genetics, says:

Human races are still extremely unstable entities in the bands of modern taxonomists…  As one goes down the scale of the taxonomic hierarchy toward the lower and lower partitions, the boundaries between clusters become even less clear.  There is great genetic variation in all populations, even in small ones. 

From a scientific point of view, the concept of race has failed to obtain any consensus… the major stereotypes, all based on skin color, hair color and form, and facial traits, reflect superficial differences that are not confirmed by deeper analysis with more reliable genetic traits and whose origin dates from recent evolution mostly under the effect of climate and perhaps sexual selection.

Now, let me make it clear that this doesn't mean that there are no differences between racial groups.  It's just that those differences are primarily social and cultural, not biological, which neatly kicks the legs out from underneath some of the racists' primary arguments.

[image courtesy of the Wikimedia Commons]

And it's been known for years that lumping together all dark-skinned Africans as "black" is ignoring the fact that there's more genetic variability on the African continent than there is in the entire rest of the world put together.  The Zulu and the !Kung people of southern Africa, for example, are more distantly related to each other than a typical white American is...

... to a person from Japan.

And just last month, Iain Mathieson of Harvard University punched another hole in racist genetics when he released his research team's findings that the genes for white skin are only about 8,000 years old.

According to Mathieson et al.:

(M)odern humans who came out of Africa to originally settle Europe about 40,000 years are presumed to have had dark skin, which is advantageous in sunny latitudes.  And the new data confirm that about 8500 years ago, early hunter-gatherers in Spain, Luxembourg, and Hungary also had darker skin:  They lacked versions of two genes—SLC24A5 and SLC45A2—that lead to depigmentation and, therefore, pale skin in Europeans today... 

Then, the first farmers from the Near East arrived in Europe; they carried both genes for light skin. As they interbred with the indigenous hunter-gatherers, one of their light-skin genes swept through Europe, so that central and southern Europeans also began to have lighter skin.  The other gene variant, SLC45A2, was at low levels until about 5800 years ago when it swept up to high frequency.

The reason the two light-skin genes took hold in northern latitudes is thought to be vitamin D synthesis -- while having dark skin is an advantage in equatorial regions, from the standpoint of protection from ultraviolet skin damage, dark skin inhibits endogenous vitamin D production in areas with low incident sunlight.  So once the mutations occurred, they spread rapidly, but only in regions at high latitude.  This explains why even distantly-related equatorial groups have dark skin (such as the Bantu and the Australian Aborigines), and even distantly-related high-latitude group have light skin (such as the Swedes and the Inuit).

And apparently the gene for blue eyes is of equally recent vintage.  The earliest genetic evidence for the gene HERC2/OCA2, which causes blue eyes, is in southern Sweden from about 7,700 years ago.  The gene's provenance might date back to 10,000 years ago, but certainly not much before that.

So all of us descend from dark-skinned, brown-eyed people.  Sorry, white supremacists.

Of course, given that there is good evidence that around 70,000 years ago, an eruption of the Toba Volcano in Indonesia caused climate shifts that killed nearly all of our ancestors -- best estimates are that there were only 10,000 humans left on Earth after the bottleneck occurred -- we're all cousins anyway.  After that event, those 10,000-odd survivors can be put into two groups; the ones who left no descendants at all, and the ones who are the ancestors of everyone on Earth.

It'd be nice if we could count on people using science to inform their behavior, but we don't have a very good track record in that regard, do we?  I mean, think about it; we're still pushing the fossil fuel industry as the world warms up and the climate destabilizes around us.  So unfortunately, even when we have direct and incontrovertible evidence that what we're doing isn't reasonable, we usually continue doing it.

And I guess the argument that the genes for white skin are 8,000 years old is going to gain no traction whatsoever with the people who believe that the Earth is 6,000 years old.

But still, it'd be nice, wouldn't it?  Just as the first photographs of the Earth taken from the Moon changed a lot of folks' perspective on our place in the universe, it'd be wonderful if research like this could alter us from "those people... they're not like us" to "we're all one family, and we're all in this together."