Smart aliens might not even live on Earthlike planets Advanced ground and space-based telescopes are discovering new planets around other stars almost daily, but an environmental scientist from England believes that even if some of those planets turn out to be Earthlike, the odds are very low they'll have intelligent inhabitants. In a recent paper published in the journal Astrobiology, Professor Andrew Watson of the University of East Anglia describes an improved mathematical model for the evolution of intelligent life as the result of a small number of discrete steps. Evolutionary step models have been used before, but Watson (a Fellow of England's Royal Society who studied under James Lovelock, inventor of the "Gaia hypothesis") sees a limiting factor: The habitability of Earth (and presumably, other living worlds) will end as the sun brightens. Like most stars, as it progresses along the main sequence, the sun's output increases (it is believed to be about 25 percent brighter now than when Earth formed). Within at most 1 billion years, this will raise Earth's average temperature to 122 degrees Fahrenheit (50 degrees Celsius), rendering the planet uninhabitable. Four major stepsApplying the limited lifespan to a stepwise model, Watson finds that approximately four major evolutionary steps were required before an intelligent civilization could develop on Earth. These steps probably included the emergence of single-celled life about half a billion years after the Earth was formed, multicellular life about a billion and a half years later, specialized cells allowing complex life forms with functional organs a billion years after that, and human language a billion years later still. Several of these steps agree with major transitions that have been observed in the geological record.
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