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Comment by JumpCrisscross | Hacker News Reader

> why couldn't multicellular life still exist?

We don't know the fundamental energy requirements of complex life. The threshold may be 2%. It may be 19.995%. If non-mitochondrial metabolism is common, the Earth would still be rare in that we'd be the "fast" biosphere. The high-octane species. Given how power-intensive intelligence is, that might be material. (Or it might not.)

More fundamentally: we have no plausible alternate chemistries that don't bootstrap on mitochondrial life. (We do for photosynthesis.)

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> Given how power-intensive intelligence is

I’m not convinced there’s a reason to think intelligence is inherently power-intensive. Based on our limited samples, it’s certainly energy intensive, but there’s no reason it couldn’t be slowed down. In a world with less power available to life, one would expect speeds of e.g. predators and prey to be slower, allowing a slower intelligence to still provide an advantage.

> not convinced there’s a reason to think intelligence is inherently power-intensive

Sure. But we know it empirically is. Our brains are expensive.

> Sure. But we know it empirically is. Our brains are expensive.

But our brains have mitochondria. As do our prey, and our predators. Is there any reason to suppose that the absence of mitochondria implies less potential for intelligence, instead of the potential for equal but slower intelligence? Mitochondria are about power production, not energy production -- they are a very dense source of ATP, but the reactions they use would provide equal energy even if less concentrated.

I think that's a little farfetched since a lot of prokaryotes show the beginning stages of complex multi-cellularity.

I don't understand why anyone would commit to so adhering to a speculative hypothesis H as to call themselves an "H-er", especially one so pointless and vague as "Rare Earth". There is some probability that a random star has intelligent life on orbiting planets, but we have no idea what that probability is. The original "Rare Earth" proposal suggested that the Earth may be the only such planet in the galaxy, but at that rate there could be hundreds of billions of Earths.

> There is some probability that a random star has intelligent life on orbiting planets, but we have no idea what that probability is.

100%. The evolutionary pattern of our solar systems formation and earth ending up, temporarily, in just the right spot isn't rare but (was) a matter of time/timing.

Now one could argue that the stellar objects carrying specific components necessary for life did not hit every or many solar systems but every single simulation (in my head) of the big bang's aftermath reveals that it's at least multiple hundreds of thousands, given how much the observable universe has revealed so far in the places that we looked.

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