The Great Filter

John K Clark (
Thu, 22 Aug 1996 22:01:05 -0700 (PDT)


I thought I'd talk a little more about Robin Hanson's 7 stages life must go
through before it can change the universe on a Cosmological scale.
Robin's 7 stages are:

1. Reproductive something (e.g. RNA)
2. Simple single-cell life
3. Complex single-cell life
4. Multi-cell life
5. Animals with big brains
6. Where we are now
7. Explosion

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.
If you define life as information that changes by natural selection then
chemist Graham Cairns-Smith says that the first life was not made of RNA but
of clay (oxides of silicon and aluminum). It's well known that clay can act
as a catalyst and store energy, it also has the most complicated chemistry of
any non biological substance. Cairns-Smith thinks clay may be able to store
information as patterns of ions or defects in the crystal lattice of large
2 dimensional sheets. As the crystals grow the patterns might be duplicated
in new layers. He wrote a book about this "Genetic Takeover And The Mineral
Origins Of Life". Also in note that in the August 8 issue of Nature is an
article about peptides acting as a self catalyst.

About stage 2 : I think simple life forms are probably easy to make, at least
on Earth it was, although I wish my reasoning was based on more than one
example. Induction certainly works better if you have more than one instance,
but that's all I have to work with. On earth life seems to have started as
soon as it possibly could, as soon as the planet cooled enough to allow
liquid water. Having got to this stage it was not easy to leave it, life
stayed stuck here for over 2 billion years.

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.

About stage 4: For long while Evolution didn't have much interest in large
brains ("Brains? We don't need no stinking brains!"). It took nature almost
570 million years to change it's mind.

About stage 5: If you went back just 3.5 million years, the time our most
famous ancestor "Lucy" was alive, the largest brain on Earth and probably the
most powerful, was not on the earth, it was in the sea. Even today the
largest brain on the planet is possessed by the Sperm Whale. I don't think
a brain, regardless of how big, is enough to get you out of this stage,
you need a hand too, and that may be even more difficult to evolve. Common
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
and it's not at all clear why. Nobody knows why bipedalism was developed,
it seems like a dumb form of locomotion, but Lucy (Australopithecus Afarensis)
could walk upright as well as you or me, and like modern humans, she had short
fingers and a fully opposable thumb. This was not very good for climbing
trees but it's great for precision gripping. From the neck down Lucy was
pretty modern, but her brain was only about as big as a modern day chimp.
After Lucy the brain increased in size at an enormous rate, and I don't think
that would have happened if Lucy didn't have such a good hand, and nobody
understands why Evolution gave her that good hand.

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.

John K Clark

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