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78 such rampant convergence on Earth, the emergence of human-level intel- ligence is a near inevitability. Engineer Brian McConnell, reviving the principle of plenitude, took this argument to an extreme. If we can’t prove that it is impossible for intelligent life to evolve elsewhere, then we should assume that it has.* Others strenuously disagree. Many experts in evolutionary biology contend that the evolution of intelligence elsewhere is extremely improb- able, implying that the Earth may be unique in harboring sentient life. There is no central line leading steadily, in a goal-directed way, from a protozoan to man, insisted Simpson. The existence of Homo sapiens depended on a very precise sequence of causative events through some 2 billion years or more; selection has taken place through long chains of nonrepetitive circumstances. It is extremely unlikely that anything enough like us for real communication of thought exists anywhere in our accessible universe.° The trouble with this reasoning is that it neglects alternate routes that converge to similar results. It is not important that the particular sequence of events leading to intelligent life on Earth be repeated elsewhere, accord- ing to the authors of the Cyclops report, but only that some sequence occur that leads to a similar end.° By implication, intelligent life on Earth could have taken a very different form. Gould believed that critics of SETI had conflated two different issues. One treats the detailed repeatability of any particular evolutionary sequence; all evolutionists have vociferously denied this specific claim. As for the general question of whether attributes that we could identify as intelligence might arise, no strong opinion can be entertained. SETI needs only the general argument to be worth doing.’ Later, Gould seemed to harden his position. Humans, he argued, arose as a fortuitous and contingent outcome of thousands of linked events, any one of which could have occurred differently and sent history on an alter- native pathway that would not have led to consciousness. The vast majority of replays would never produce a creature with self-consciousness; the chance that this alternative will contain anything remotely like a human being must be effectively nil.* Arthur Clarke put this in a more positive way. There still might be intel- ligence on this planet if the terrestrial experiment started all over again, but it wouldn’t look like us. In the dance of the DNA spirals, the same partners would never meet again.’ If consciousness is just an insignificant accident, an incidental outcome of random mutational processes, searches for extraterrestrial intelligence are unlikely to succeed. However, posited Davies, if we accept that mind is an emergent phenomenon requiring a certain critical level of complexity, we can imagine that level of complexity being achieved, given long enough and given the inherent self-organizing tendencies that we find in matter and energy. Probabilities: Intelligence