By James Horton and Tiffany Taylor
What would happen if the hands of time were turned back to an arbitrary point in our evolutionary history and we restarted the clock? American palaeontologist Stephen Jay Gould proposed this famous thought experiment in the late 1980s – and it still grips the imagination of evolutionary biologists today.
Gould reckoned that if time was rewound, then evolution would drive life down a completely different path and humans would never re-evolve. In fact, he felt humanity’s evolution was so rare that we could replay the tape of life a million times and we wouldn’t see anything like Homo sapiens arise again.
His reasoning was that chance events play a huge role in evolution. These include enormous mass extinction events – such as cataclysmic asteroid impacts and volcanic eruptions. But chance events also operate at the molecular scale. Genetic mutation, which forms the basis of evolutionary adaptation, is reliant on chance events.
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