The statistical chances of their being other intelligent life in the universe are “exceptionally rare,” according to a new study from the University of Oxford.
In the paper, scientists from Oxford’s Future of Humanity Institute, theorize that as life evolved on earth, in many cases it depended on a series of unlikely “revolutionary transitions.” Given how late intelligent life evolved on this planet, the chances of similar developments happening on other planets, before they are no longer able to sustain life, were highly unlikely, they said.
“It took approximately 4.5 billion years for a series of evolutionary transitions resulting in intelligent life to unfold on Earth,” they wrote in the paper published last month. “In another billion years, the increasing luminosity of the Sun will make Earth uninhabitable for complex life.
“Together with the dispersed timing of key evolutionary transitions and plausible priors, one can conclude that the expected transition times likely exceed the lifetime of Earth, perhaps by many orders of magnitude,” the wrote. “In turn, this suggests that intelligent life is likely to be exceptionally rare.”
To reach their conclusions, the scientist looked at statistical models to determine the probability that the sequence of evolutionary transitions that occurred on Earth, could occur elsewhere.
“We made use of the assumption that what happened on Earth is typical for what happens on other planets – not the exact times, but that there are some tricky steps life needs to get through in sequence to produce intelligent observers,” Oxford’s Anders Sandberg told the Daily Mail.
The paper points to the fact that it took more than a billion years for life to advance from prokaryotic (single-cell organisms) to eukaryotes (organisms with a nucleus) means that such a step is highly unlikely.
It also notes that humans have only existed on Earth for about the last 6 million years, with homo sapiens, only arriving some 200,000 years ago.
“Some transitions seem to have occurred only once in Earth’s history, suggesting a hypothesis reminiscent of Gould’s remark that if the ‘tape of life’ were to be rerun, ‘the chance becomes vanishingly small that anything like human intelligence’ would occur,” the paper says referring to the quote from evolutionary biologist Stephen Jay Gould.
“What we added was a statistical approach that allows us to get estimates of just how unlikely the steps could be,” Sandberg said. “We feed in data about when things happened on Earth and a guess of how many steps there were, and in return we get the most likely levels of difficulty.”
“[These] turn out to indicate that, yes, we are an unlikely planet,” he said.
However, Sandberg noted that just because scenarios of intelligent life on other plants were improbable, doesn’t mean humans should stop searching.
“Just because we got our results doesn’t mean it is a waste of time to look at the actual universe,” he said. “Data will always trump ever so careful reasoning and statistics.”