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Statisticians say that intelligent life evolution is “exceptionally rare” and that human-like civilizations are extremely unlikely to exist on other planets.
In a new paper, Oxford researchers theorize that for life to evolve the same way in other parts of the universe it would take longer than Earth’s entire predicted lifespan.
Evolution on Earth from the Big Bang to the present day has involved a series of what they call “evolutionary transitions” that have been aided by chance.
These include the emergence of primitive life from nonliving matter (known as abiogenesis) and eukaryotic life (with cells that have an enclosed nucleus), the evolution of sexual reproduction, multicellularity and intelligence itself.
If intelligent life exists on other planets, it should have gone through a series of comparable evolutionary transitions.
The research is based on the Fermi paradox, which is the apparent contradiction between the lack of evidence for extraterrestrial civilizations and various high estimates for their probability.
“It took about 4.5 billion years for a series of evolutionary transitions that led to intelligent life to take place on Earth,” experts from the Future of Humanity Institute at Oxford University say in their paper.
‘In another billion years, the rising brightness of the Sun will make the Earth uninhabitable for a complex life.
“Together with the scattered times of key evolutionary transitions and plausible precedents, it can be concluded that the predicted transition times are likely to exceed the lifespan of the Earth, perhaps by many orders of magnitude.
“In turn, this suggests that intelligent life is likely to be exceptionally rare.”
The researchers used a special statistical technique called “Bayesian analysis” to determine the likelihood of events in Earth’s history – a “chain of multiple evolutionary transitions” – happening elsewhere.
“Our methods were basically statistical,” Dr. Anders Sandberg of the Future of Humanity Institute.
“We used the hypothesis that what happened on Earth is typical of what happens on other planets, not the exact timing, but that there are some complicated steps that life has to take in sequence to produce intelligent observers.”
For example, eukaryotes – organisms with a nucleus – needed more than a billion years ago to emerge from their coreless prokaryotic predecessors.
This was a much less likely event than the development of multicellular life, which is thought to have originated independently over 40 times in nature.
The fact that some transitions have only occurred once in Earth’s history suggests a remarkable stroke of luck that brought intelligent Earthlings today.
The team cites American evolutionary biologist Stephen Jay Gould, who said that if the “tape of life” were to be repeated, “the chance becomes incredibly small that something similar to human intelligence will occur.”
“What we added was a statistical approach that allows us to get estimates of how unlikely the steps might be,” said Dr. Sandberg at MailOnline.
“We provide data on when things happened on Earth and a hypothesis of how many steps there have been, and in return we get the most likely difficulty levels.
‘[These] turn out to indicate that, yes, we are an unlikely planet. ‘
Coming to the opposite conclusion – that life in the universe is by no means uncommon – would require evidence for transitions much earlier than those on Earth, or more instances of transitions.
The classic version of this argument comes from the work of Australian theoretical physicist Brandon Carter, who sought to explain why intelligent life emerged so late in Earth’s history.
The Earth is 4.5 billion years old, and in another billion years, the rising brightness of the Sun will likely destroy the Earth’s ability to support complex life, due to rising surface temperatures.
But humans, including our ape-like ancestors who walked on two legs, have only existed on Earth for about 6 million years.
Homo sapiens, meanwhile, arrived about 200,000 years ago.
‘[Carter] pointed out that there is no reason to think that complicated passages on average may take much longer than planets remain habitable, “said Dr.
“There may be completely different kinds of life and minds, but they are likely to evolve just as (or harder) as we do.”
Dr. Sandberg added that the new study fits into what might be called “chairside astrobiology” as it deals with probability.
“Just because we got our results doesn’t mean it’s a waste of time looking at the real universe,” he said.
“The data will always win over such accurate reasoning and statistics.”
This article has been adapted from its original source.
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