[ExI] New paper from Anders on rarity of intelligent life

[Dylan Distasio]

Abstract
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.

https://www.liebertpub.com/doi/10.1089/ast.2019.2149
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