[ExI] The 'Rare Earth' theory might not be rare after all

[BillK]

We Might Not Be So Strange
Philip Ball    Fri, October 24, 2025

<https://www.yahoo.com/news/articles/might-not-strange-095000194.html>
Quote:
Lucky how? Carter argued that, in order to reach human-like intelligence,
life here had to clear several hurdles that involve rare, chance events: a
gauntlet of “hard steps” along the way.
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A new proposal argues that these "hard steps" may not be unusual after all.
I asked Claude Sonnet 4.5 to summarise this long article.
BillK

Claude Sonnet 4,5

This article challenges a long-standing argument about why intelligent life
might be extremely rare in the universe.

*The Original Puzzle*

In 1983, physicist Brandon Carter noted a curious coincidence: humans
evolved roughly halfway through Earth's habitable lifespan (about 4.6
billion years in, with another 5 billion before the sun dies). He argued
this timing suggests intelligence requires clearing several extremely rare
"hard steps" - evolutionary breakthroughs so unlikely they might happen
only once per planet, if at all. Examples include the origin of life,
oxygen-producing photosynthesis, complex cells (eukaryotes), and
human-level cognition.

*The New Challenge*

Geomicrobiologist Daniel Mills and colleagues now argue these "hard steps"
might not be inherently rare or difficult at all. Instead, they propose two
key insights:

   1. *Winner-takes-all evolution*: Once a lineage achieves a breakthrough,
   it dominates its niche so completely that other attempts never get a
   foothold - making transitions appear unique when they weren't necessarily
   unlikely.
   2. *Environmental pacing*: Life had to wait for Earth itself to become
   ready. For instance, complex life needed oxygen levels that only stabilized
   400 million years ago - meaning for 90% of Earth's history, humans
   physically couldn't exist regardless of evolutionary progress.

*The Implications*

If Mills is correct, intelligent life might be common but simply takes
billions of years to emerge anywhere because planets themselves need time
to become habitable. We could test this by examining exoplanet atmospheres
- if we find many with oxygen or other biosignatures, it would support the
idea that life develops readily given the right conditions. The debate may
be resolved this century as telescope technology improves.

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