Blue Highway Corridor

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News Excerpt:

According to a new study published in the journal Nature, The most recent and widespread migration of humans out of Africa, which occurred less than 1,00,000 years ago, may have taken place during a particularly arid period following the Toba supervolcano eruption in Indonesia.


Important Points:

  • It is typically thought that the dispersals of humans out of Africa occurred during humid periods that created ‘green corridors’ and facilitated the movement of people. 
  • Periods of aridity are thought to have constrained human movement and created food insecurity.

Key observations of the Study:

  • Researchers studied a site in northwest Ethiopia, near the Shinfa River, that holds evidence of a human presence in the form of chipped stone from tool manufacturing and animal remains. 
    • Chemical analysis of glass shards in sediment samples revealed they were from the Toba supereruption, which places the presence of humans at this location at around 74,000 years ago, in the Middle Stone Age (roughly 280,000 to 50,000 thousand years ago). 
    • Oxygen isotopes from ostrich eggshells and fossil mammal teeth indicate that the environment at this time was particularly arid.
  • This increased aridity — paradoxically — explains the increased reliance on fish at the site at this time and suggests that, as the river shrank in the dry season, fish were trapped in waterholes where they could easily be targeted by hunters, perhaps using bows and arrows. 
    • Adaptive foraging along dry-season waterholes would have transformed seasonal rivers into ‘blue highway’ corridors, potentially facilitating an out-of-Africa dispersal and suggesting that the event was not restricted to times of humid climates.
  • The arid conditions might have triggered and necessitated movement, spurred along by the intrinsic attributes of seasonal rivers.
  • As per the author, the behavioural flexibility documented at the site, which helped these humans to survive the aftermath of the supereruption, was probably critical for modern humans to prosper in the diverse climates and habitats that they encountered during their eventual dispersal out of Africa and expansion across the world.

How did humans survive the Mount Toba eruptions?

  • Adapting to adversity: At the Shinfa-Metema 1 site, humans showed remarkable resilience, continuing life despite the eruption's aftermath. They adapted to the drier conditions by altering their diets and exploiting local resources.
  • Clever diet shift: Instead of relying solely on land animals for food, humans turned to fish. As the landscape changed, shallow waterholes formed, making fish easier to catch. This flexibility in diet proved crucial for survival.
  • Migration insights: The study challenges traditional theories of human migration out of Africa. Instead of waiting for hospitable "green corridors," humans might have followed "blue highways," navigating seasonal rivers to new territories.
  • Advanced technology: Excavations uncovered evidence of advanced tools, including stone points believed to be arrowheads. This suggests early humans were adept hunters, capable of innovation even in challenging environments.

Debates and discoveries related to the Toba eruption

  • While the study offers compelling evidence, experts continue to debate the exact impact of the Toba eruption. 
  • Nonetheless, it sheds light on the resourcefulness of early human populations in the face of adversity.

Implications for understanding human history 

  • By understanding how our ancestors survived cataclysmic events, we gain valuable insights into the evolution and migration of our species, Homo sapiens.

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