AstrobiologyAhead of PrintResearch ArticleOpen Access
Open Access license
https://www.liebertpub.com/doi/10.1089/ast.2019.2149
The Timing of Evolutionary Transitions Suggests Intelligent Life Is Rare
Andrew E. Snyder-Beattie, Anders Sandberg, K. Eric Drexler, and Michael B. Bonsall
Published Online:19 Nov 2020https://doi.org/10.1089/ast.2019.2149
Astract
It is unknown how abundant extraterrestrial life is, or whether such life might be complex or intelligent. On Earth, the emergence of complex intelligent life required a preceding series of evolutionary transitions such as abiogenesis, eukaryogenesis, and the evolution of sexual reproduction, multicellularity, and intelligence itself. Some of these transitions could have been extraordinarily improbable, even in conducive environments. The emergence of intelligent life late in Earth's lifetime is thought to be evidence for a handful of rare evolutionary transitions, but the timing of other evolutionary transitions in the fossil record is yet to be analyzed in a similar framework. Using a simplified Bayesian model that combines uninformative priors and the timing of evolutionary transitions, we demonstrate that expected evolutionary transition times likely exceed the lifetime of Earth, perhaps by many orders of magnitude. Our results corroborate the original argument suggested by Brandon Carter that intelligent life in the Universe is exceptionally rare, assuming that intelligent life elsewhere requires analogous evolutionary transitions. Arriving at the opposite conclusion would require exceptionally conservative priors, evidence for much earlier transitions, multiple instances of transitions, or an alternative model that can explain why evolutionary transitions took hundreds of millions of years without appealing to rare chance events. Although the model is simple, it provides an initial basis for evaluating how varying biological assumptions and fossil record data impact the probability of evolving intelligent life, and also provides a number of testable predictions, such as that some biological paradoxes will remain unresolved and that planets orbiting M dwarf stars are uninhabitable.
7. Conclusions
It took approximately 4.5 billion years for a series of evolutionary transitions resulting in intelligent life to unfold on Earth. In another billion years, the increasing luminosity of the Sun will make Earth uninhabitable for complex life. Intelligence therefore emerged late in Earth's lifetime. 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. In turn, this suggests that intelligent life is likely to be exceptionally rare. Arriving at an alternative conclusion would require either exceptionally conservative priors, finding additional instances of evolutionary transitions, or adopting an alternative model that can explain why evolutionary transitions took so long on Earth without appealing to rare stochastic occurrences. The model provides a number of other testable predictions, including that M dwarf stars are uninhabitable, that many biological paradoxes will remain unsolved without allowing for extremely unlikely events, and that, counterintuitively, we might be slightly more likely to find simple life on Mars.
Intelligent Life Really Can't Exist Anywhere Else
Hell, our own evolution on Earth was pure luck.
https://www.popularmechanics.com/science/a34771475/does-intelligent-life-exist-elsewhere/
NOV 24, 2020
In newly published research from Oxford University's Future of Humanity Institute, scientists study the likelihood of key times for evolution of life on Earth and conclude that it would be virtually impossible for that life to evolve the same way somewhere else.
Life has come a very long way in a very short time on Earth, relatively speaking—and scientists say that represents even more improbable luck for intelligent life that is rare to begin with.
For decades, scientists and even philosophers have chased many explanations for the Fermi paradox. How, in an infinitely big universe, can we be the only intelligent life we’ve ever encountered? Even on Earth itself, they wonder, how are we the only species that ever has evolved advanced intelligence?
There are countless naturally occurring, but extremely lucky ways in which Earth is special, sheltered, protected, and encouraged to have evolved life. And some key moments of emerging life seem much more likely than others, based on what really did happen.
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“The fact that eukaryotic life took over a billion years to emerge from prokaryotic precursors suggests it is a far less probable event than the development of multicellular life, which is thought to have originated independently over 40 times,” the researchers explain. They continue:
“The early emergence of abiogenesis is one example that is frequently cited as evidence that simple life must be fairly common throughout the Universe. By using the timing of evolutionary transitions to estimate the rates of transition, we can derive information about the likelihood of a given transition even if it occurred only once in Earth's history.”
In this paper, researchers from Oxford University’s illustrious Future of Humanity Institute continue to wonder how all this can be and what it means. The researchers include mathematical ecologists, who do a kind of forensic mathematics of Earth’s history.
In this case, they’ve used a Bayesian model of factors related to evolutionary transitions, which are the key points where life on Earth has turned from ooze to eukaryotes, for example, and from fission and other asexual reproduction to sexual reproduction, which greatly accelerates the rate of mutation and development of species by mixing DNA as a matter of course.
Most of these “evolutionary transitions” are poorly understood and have not been very well studied by the scientists of likelihoods. And using their model, these scientists say that Earth’s series of Goldilocks lottery tickets are more likely to have taken far longer than they really did on Earth.
There’s an iconic scene in the 2001 movie Ocean’s Eleven where George Clooney explains the series of escalating improbabilities of his planned crime. After several hugely unlikely outcomes, he says, “Then it's a piece of cake: just three more guards with Uzis, and the most elaborate vault door conceived by man.” In a way, the unlikely hurdles to the rapid flourishing of complex life on Earth are the same way.
First, we win the lottery for surface temperature and protection from spaceborne dangers. Second, we win the lottery for the presence of building blocks of life. Third, we win the lottery for the right location for the right building blocks. That’s before anything like the most primitive single cell has even emerged.
Using some information we do know, like the age of Earth and the expected end of its habitable lifetime due to the expanding heat radius of our sun, these researchers have turned evolutionary transitions into a series of existential scratch-off tickets. Read the whole fascinating study here.
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