Re: EVOLUTION: Stress needed for diversity?

Date: Sat Mar 18 2000 - 20:58:14 MST

Robert J. Bradbury, <>, writes:
> For those of you who didn't catch it, the January 2K issue of Scientific
> American had an interesting article on "Snowball Earth":
> The snowball earth events where the CO2 recycler got jammed by the
> continents clustering around the equator (maybe), causing the earth to go
> through freezings (-50C) followed by heat waves (+50C) lasting tens of
> millions of years. During the ice periods all of the continents and oceans
> would have been buried in several km of ice. There is no evaporation
> from the oceans covered in ice and even if they weren't, the cold would
> produce low evaporation rates.

The more I hear about these catastrophic behavior patterns of the earth,
the less I hear about James Lovelock's Gaia hypothesis. His idea was
that the earth was a single, global super-organism, which regulated its
own temperature and "internal" environment just like other organisms.
This is why the earth has been so "mild".

Now that it appears that earth may not have always been so congenial,
it makes Lovelock's already-tenuous hypothesis look even more unlikely.

The big problem I always had with the Gaia idea is that organisms can
control their internal environmens only because they have evolved this
ability over many generations. Early organisms were probably bad at it,
but those which were slightly better survived and reproduced, and over
time the ability improved.

I don't see any way such a mechanism can operate at the level of the
single global super-organism, if we choose to look at life that way.
It is a single immortal living entity; it does not reproduce, it
does not compete with other organisms, hence it cannot evolve in
the Darwinian sense. An incompetent Gaia simply dies. A successful
one lives until something happens that it can't handle, then it dies.
There are no progeny to carry on the genes, no sources of variation and
selection to evolve ever more successful generations of Gaia organisms.

Of course some people choose to interpret out own technologies as
developing Gaia's reproductive organs, our eventual interplanetary
colonization efforts being Gaia's production of ova and sperm to go out
and fertilize the universe. Even if this view has some validity, it
doesn't shed any light on why or how Gaia has survived as long as she has.

I find myself leaning towards the view that we simply got very,
very lucky. Life's survival on earth was an incredible fluke, a one
in a trillion chance. Most planets kill off their life before it gets
this far. It's an optimistic approach, explaining the Fermi paradox by
putting most of Robin Hanson's "great filter" behind us.


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