Humans evolved as an invasive species

 

australopithecus_afarensis2

Until this prehistoric hominid changed its diet to meat-centered,
expanding its brain to enable complex tool and weapon-making,
it was easy prey for the saber-toothed tiger.

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How Homo sapiens Became the Ultimate Invasive Species

Many human species have inhabited Earth. But ours is the only one that colonized the entire planet. A new hypothesis explains why

By Curtis W. Marean | Jul 14, 2015, Scientific American

Sometime after 70,000 years ago our species, Homo sapiens, left Africa to begin its inexorable spread across the globe. Other human species had established themselves in Europe and Asia, but only our H. sapiens ancestors ultimately managed to push out into all the major continents and many island chains. Theirs was no ordinary dispersal. Everywhere H. sapiens went, massive ecological changes followed. The archaic humans they encountered went extinct, as did vast numbers of animal species. It was, without a doubt, the most consequential migration event in the history of our planet.

Paleoanthropologists have long debated how and why modern humans alone accomplished this astonishing feat of dissemination and dominion. Some experts argue that the evolution of a larger, more sophisticated brain allowed our ancestors to push into new lands and cope with the unfamiliar challenges they faced there.

Others contend that novel technology drove the expansion of our species out of Africa by allowing early modern humans to hunt prey —and dispatch enemies—with unprecedented efficiency. A third scenario holds that climate change weakened the populations of Neandertals and other archaic human species that were occupying the territories outside Africa, allowing modern humans to get the upper hand and take over their turf. Yet none of these hypotheses provides a comprehensive theory that can explain the full extent of H. sapiens‘ reach. Indeed, these theories have mostly been proffered as explanations for records of H. sapiens activity in particular regions, such as western Europe. This piecemeal approach to studying H. sapiens‘ colonization of the earth has misled scientists. The great human diaspora was one event with several phases and therefore needs to be investigated as a single research question.

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