The Great Filter

Robin Hanson (
Fri, 23 Aug 96 10:34:42 PDT

John K Clark writes:
>About stage 1: Although organisms that used only RNA would be much simpler
>than modern creatures that make use of DNA, RNA and proteins, some think
>they would still be too sophisticated to be the first forms of life.

Yes. I didn't put this other step on the list because I don't know of
a good neutral name for it.

>On earth life seems to have started as soon as it possibly could, as
>soon as the planet cooled enough to allow liquid water.

I'm not sure we know that. There was a billion years (a long time
really) between the time the Earth formed and the oldest known life

>Having got to this stage it was not easy to leave it, life stayed
>stuck here for over 2 billion years.

Only 1.7 billion years, actually.

>About stage 3: It must be hard to make a multicellular life form that is good
>enough to compete with single cell life, it took a long time to figure out
>how to do it. Live was stuck here for about 700 million years.

For Great Filter issues, "hard" would be expected times of a trillion
years or more. An expected times 700my is far from hard enough to matter.

>sense would indicate that a large brain must come first because a hand is of
>no use if you don't have a big brain to direct it, but common sense is wrong

Good point. List has been changed accordingly.

>About stage 6: If we ever get out of this stage we'll do it in less than a
>thousand years, probably a lot less. It appears that each stage is shorter
>than the one before.

This is likely to be a New Yorker's view of the world phenomena. The
really hard stages, I think, do not cluster near us in time.

Robin Hanson