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 Earth-like, 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 the 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 the Earth formed). Within at most 1 billion years, this will raise the average temperature of the Earth to 50 degrees C, rendering the planet uninhabitable.
Four major steps
Applying 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 archeological record.
Watson estimates the overall probability that intelligent life will evolve as the product of the probabilities of each of the necessary steps. In his model, the probability of each evolutionary step occurring in any given epoch is 10 percent or less, so the total probability that intelligent life will emerge is quite low (less than 0.01 percent over 4 billion years). Even if intelligent life eventually emerges, the model suggests its persistence will be relatively short by comparison to the lifespan of the planet on which it developed.
The mathematical methods Watson used assume that each evolutionary step is independent of the others, though they must occur in sequence. Watson considers this "a reasonable first approximation for what is, after all, a very idealized sort of model, deliberately simplified enough that the math can be solved analytically."
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 the 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 the Earth formed). Within at most 1 billion years, this will raise the average temperature of the Earth to 50 degrees C, rendering the planet uninhabitable.
Four major steps
Applying 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 archeological record.
Watson estimates the overall probability that intelligent life will evolve as the product of the probabilities of each of the necessary steps. In his model, the probability of each evolutionary step occurring in any given epoch is 10 percent or less, so the total probability that intelligent life will emerge is quite low (less than 0.01 percent over 4 billion years). Even if intelligent life eventually emerges, the model suggests its persistence will be relatively short by comparison to the lifespan of the planet on which it developed.
The mathematical methods Watson used assume that each evolutionary step is independent of the others, though they must occur in sequence. Watson considers this "a reasonable first approximation for what is, after all, a very idealized sort of model, deliberately simplified enough that the math can be solved analytically."
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