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by Mbioguy
2657 days ago
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Nothing in evolution is inevitable. Granted some things are more likely (oxygen-binding hemoglobin has independently evolved several times from its related non-binding globin family). Brains, nervous systems, even multicellularity are not inevitable. The specific combination of astronomical, geological, and biological features that lead to our development might not lead to similar outcomes if ran a million times. As other responders have pointed out, brains are just one possible substrate for intelligence. We can't account for other systems (biological or otherwise) that could lead to the development of intelligence, so of necessity any probability estimate based on us has to be a lower bound of possibility. One bit of our earth history that is worth noting is that the conditions when life presumably arose are hostile to multicellular life as we know it. Earth's early oceans were hot, anoxic and reducing, and under heavy pressure from far thicker atmospheres. The great oxidation event essentially turned earth's atmosphere into a bacterial waste dump, the waste being oxygen produced by early cyanobacteria. Life had to evolve ways to cope with oxygen or learn to hide. This is still true of our own cells. While we need oxygen to survive, it is still and will always be toxic. Free radical damage such as from reactive oxygen species is a constant threat, and is the ultimate form of irrecoverable information death when we die. Might it be that the conditions under which life can arise, and under which intelligent life can arise, are different? We got lucky that earth traversed from the first to the second. Add this to the list of a million things that had to go right for us to exist at all. The same might well be true of any other intelligences out there. And the odds of two arising close enough in time and space to contact each other would be far less common than lonely civilizations looking out into the dark. |
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It took 2 billion years for the hard-working unicellular cyanobacteria to produce enough oxygen to first oxidize the rocks and minerals on the Earth's surface, and to build up enough oxygen in the atmosphere for the birth of multicellular life to be possible.
But if the planed had only supported one half of the cyanobacterial biomass it did, or if the amount of rocks to oxidize, or the mass of the atmosphere, was larger, that 2 billion years could have as well taken e.g. 4 billion years. And the Sun would have already become too hot, and multicellular life would never have evolved.
https://en.wikipedia.org/wiki/Great_Oxygenation_Event