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Probabilities: Intelligence The immediate pressure of necessity has brightened their intellects, enlarged their powers, and hardened their hearts. —H.G. Wells, describing Martians, 1897! Intelligence may be the most controversial factor in the Drake equation. Schilling found that the question of whether intelligence is inevitable is currently what most polarizes the discussion about SETI; there seems to be no middle ground. Some scientists see it as the crucial bottleneck in the Drake equation.” Those who think that intelligence is likely to emerge on other planets emphasize the early appearance of life on Earth, which suggests that life on other worlds may have a long time to evolve intelligent beings. Our planet produced an advanced technological civilization “only” 4 billion years after it formed; the Earth may have a billion good years ahead before life is destroyed by an expanding Sun. Sagan and Drake were more upbeat, claiming that intelligence and tech- nology have developed on the Earth about halfway through the stable period in the life of our star. By contrast, physicist Brandon Carter argued that the time that most home stars remain stable would not be enough to allow the evolution of intelligent beings. Earth, he declared, is not typical, but an exception.* Those optimistic about the emergence of intelligence cite generalized processes such as parallel or convergent evolution, noting that some Earthly species other than Homo sapiens show signs of intelligence. The many biological parallels to those features that define the emergence of humans, Morris argued, suggest that something similar will emerge elsewhere. Some features are so adaptive that they are essentially inevitable—like the ability to see, and the intelligence and self-awareness that characterize us. Given 77 Inevitable, or a Fluke?