Why Intelligent Life Might Be Extremely Rare In the Universe

Are we alone in the universe? The Fermi Paradox is the contradiction between the apparent probability of extraterrestrial life, given the vast number of stars and planets in the universe, and the absence of strong evidence for extraterrestrial intelligence. If we are alone, why? A survey of evolutionary history suggests that a series of unique one-off events- the evolution of photosynthesis, sex, complex cells, complex animals, the bony skeleton, and human intelligence- were unique, one-off events that only happened once in Earth's 4.5 billion year history. The evolution of life itself was also a unique event. The fact that each event happened only once in our history suggests that the big steps that led to our evolution were highly improbable- and that they might not happen on all planets where life appears.