My inner geek thinks about the BSG idea of reducing a population to very few survivors. Or the Lord of the Rings idea that Middle Earth existed in our far past. Or the idea that we came to the level of swords and sandals inside of 10,000 of discoveries. Could the populations and species of pre-Toba Earth lived together in a wild dynamic (savage Homo Erectus infested lands vs. Neanderthal and Homo Sapien tribes or villages)? With almost all of the genetic diversity still intact, what did these Homo Sapiens look like after millenia of diversification before their lines were cut short? What social organizations did they form? Our models have been handed down from small pools of survivors-- did these pre-Toba people have something better that was wiped out by a mega-volcano?
I can't believe I didn't hear about this theory until I read this Wikipedia article.
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, including Homo habilis, H. ergaster, H. erectus, H. neanderthalensis, H. sapiens, and possibly H. floresiensis.
According to the Toba catastrophe theory, the consequences of a massive volcanic eruption drove the world's human population to the brink of extinction between 70,000–75,000 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 1 gigaton of TNT (4.2 EJ), about three thousand times greater than the 1980 eruption of Mount St. Helens, and forty times greater than the largest human-made explosion, the October 30, 1961 detonation of the Soviet Union's Tsar Bomba thermonuclear device. It is hypothesized that the Toba explosion may have reduced the average global temperature by 3–5 °C (5–9 °F) for several years and triggered an ice age. According to Alan Robock et al., the Toba incident did not initiate an ice age, but rather exacerbated an ice age that had already been underway. The simulations demonstrated a maximum global cooling down of around 15 °C, approximately 3 years after the eruption (6 Gt SO2/ 300 × 1991 Mount Pinatubo eruption). As the saturated adiabatic lapse rate is 4.9 °C/ 1,000 m for temperatures above freezing, this means that the Tree line and the Snow line were around 3,000 m (9,000 ft) lower at this time. Nevertheless, the climate recovered over a few decades.
Ambrose proposes that this massive environmental change created population bottlenecks in the species that existed at the time; this in turn accelerated differentiation of the isolated human populations, eventually leading to the extinction of all the other human species except for the two branches that became Neanderthals (Homo neanderthalensis) and modern humans (Homo sapiens). More recently several geneticists, including Lynn Jorde and Henry Harpending have proposed that the human race was reduced to approximately five to ten thousand people.
Some geological evidence and computed models support the plausibility of the Toba catastrophe theory. Ashes from this eruption of Lake Toba, located near the equator, should have spread all over the world. While the Greenland ice core data displays an abrupt change around this time, changes in the corresponding Antarctic data are not easily discernible.
Genetic evidence suggests that all humans alive today, despite apparent variety, are descended from a very small population, perhaps between 1,000 to 10,000 breeding pairs about 70,000 years ago.
Gene analysis of some genes shows divergence anywhere from 60,000 to 2 million years ago, but this does not contradict the Toba theory, once again because Toba is not conjectured to be an extreme bottleneck event. The complete picture of gene lineages (including present-day levels of human genetic variation) allows the theory of a Toba-induced human population bottleneck.
Analysis of louse genes
Alan Rogers, a co-author of this study and professor of anthropology at the University of Utah, says: “The record of our past is written in our parasites.” Rogers and others have proposed the bottleneck may have occurred because of a mass die-off of early humans due to a globally catastrophic volcanic eruption. The analysis of louse genes confirmed that the population of Homo sapiens mushroomed after a small band of early humans left Africa sometime between 150,000 and 50,000 years ago.
Analysis of Helicobacter pylori genes
Recent research states that genetic diversity in the pathogenic bacterium Helicobacter pylori decreases with geographic distance from East Africa, the birthplace of modern humans. Using the genetic diversity data, the researchers have created simulations that indicate the bacteria seems to have spread from East Africa around 58,000 years ago. Their results indicate modern humans were already infected by H. pylori before their migrations out of Africa, and H. pylori remained associated with human hosts since that time.
Migration after Toba
It is currently not known where human populations were living at the time of the eruption. The simplest scenario would be that all the survivors were populations living in Africa, whose descendants would go on to populate the world. However, recent archeological finds, mentioned above, have suggested that a human population may have survived in India. Dating of early human migrations cannot yet give a conclusive answer to this question. Recent analyses of mitochondrial DNA have set the estimate for the major migration from Africa to 60–70,000 years ago, whereas the Toba eruption has been dated to 67,500–75,500 years ago. Either from Africa or from South Asia, during the next tens of thousands of years the surviving populations would populate Australia, East Asia, Europe and the Americas.