Are we alone in the universe? It comes down to whether intelligence is a probable outcome of natural selection, or an improbable fluke. By definition, probable events occur frequently, improbable events occur rarely—or once. Our evolutionary history shows that many key adaptations—not just intelligence, but complex animals, complex cells, photosynthesis, and life itself—were unique, one-off events, and therefore highly improbable. Our evolution may have been like winning the lottery … only far less likely.
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Source: Phys.org