No ark required. Animals survived just fine when a flood of lava erupted from the Toba supervolcano 74,000 years, plunging Earth into a volcanic winter. At least that's what a new gene study suggests.
The new analysis casts doubt on a theory that humans were almost wiped out by the fall-out from the eruption. This comes from a pattern in genetic data called a bottleneck, which suggests that a population has rapidly expanded after recently collapsing.
If Toba caused such a collapse, humans would not have been the only ones affected by the bottleneck, reasoned Geoffrey Hayes of Northwestern University in Chicago.
His team examined the mitochondrial DNA of 19 mammal species from every continent, comparing genetic diversity in different individuals of the same species, looking for similar patterns. The bottleneck showed up in seven of the species, but only coincided with Toba in two – the Siberian roe deer and Chinese black snub-nosed monkey.
Hayes adds that because the volcanic winter would have been most severe around Indonesia where Toba is situated, so species in that area should have been more affected. But his analysis shows some species living near or on the archipelago didn't go through a bottleneck.
The new study is not proof: Toba might still have devastated the human population, Hayes says, but it is another piece of evidence against it. Others have suggested that the population growth spurt could have been prompted by our ancestors' movement out of Africa at this time.
"This is an interesting and welcome study," says Michael Petraglia of the University of Oxford. He cautions that pinpointing the date of genetic events is very imprecise but says the findings fit with archaeological data that suggests humans in India lived through the eruption.
But Stanley Ambrose of the University of Illinois in Urbana-Champaign, who was among the first to formulate the Toba theory, says other species may tell a different tale. He says fossil evidence suggests that macaques and tigers bottlenecked at the right time, and other animals such as such as orang-utans went extinct throughout most of south-east Asia around the time of the eruption, while others – gorillas and chimpanzees, for example – split into different lineages. Ambrose suggests surviving populations may have been larger, better adapted, or affected differently by climatic change as a result of the eruption.
Hayes, who presented the work at the Society for Molecular Biology and Evolution meeting in Chicago this month, says he intends to examine more animal species, as well as the chloroplasts of plants that would have been affected by the darkened skies after the eruption.
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