Can the 'hard steps' in the evolutionary history of human intelligence be recast with geological thresholds? - Phys.org

What took so long for humans to appear on Earth? The Earth is 4.6 billion years old, and life began about 4 billion years ago, yet humans—the only intelligent, technological species we know of in the universe—have existed only for the last 200,000 years. Ads Links by Easy Branches
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