[extropy-chat] Re: Intelligent Design and Irriducible Complexity

[Hal Finney]

Another problem with this Bayesian argument is, why did the Intelligent
Designer only choose to create life on Earth?  If we assume that he has
no limits to his power (as suggested by p(L|ID)=1, i.e. he could not
fail to achieve his goal), then why would he not create life on every
planet in the solar system?

And this illustrates the flaw in assuming p(ID)=0.5.  If ID specifically
means "Intelligent Design directed towards creating life on Earth",
imagine IDm as "Intelligent Design directed towards creating life on
Earth and Mars".  And IDmj is "Intelligent Design directed towards
creating life on Earth, Mars and Jupiter".  We can conceive of a whole
series of ID variants.  Each of them is more restrictive or encompassing
than the others.

We have no idea what the probability of each one is.  But we surely
cannot set the probability for all of ID, IDm, IDmj, and all of the
others, to 0.5.  Some include the others, so the probabilities have to
be different.  We can't set every unknown probability to 0.5.

The correct solution is to think harder about ID and come up with a better
estimate for p(ID).  You have to think about his likely motivations and
power.  This may seem difficult, but if you are seriously considering ID
as an explanation for life on Earth, you have to have some conception
of how exactly that happened, what the circumstances were, how the ID
happened to choose Earth and how it performed the creation.  Even if
you can make only imperfect guesses at these details, they will guide
you to an estimate of the probability of the overall situation.

And of course you need to estimate the probability that the Intelligent
Designer exists and came to Earth in the first place, as part of the
probability estimate.  This requires you to consider how the ID itself
may have arisen, consider a mechanism for it to have been created,
and estimate a probability for that mechanism.

Only once you have done this analysis can you come up with an a priori
probability estimate for p(ID), and p(L|ID).  I don't think you actually
should set the latter to 1, unless your ID is by definition omnipotent in
which case you should lower p(ID) correspondingly.  But we can certainly
imagine less than omnipotent intelligences who struggled to seed Earth
with a life form that could survive in early conditions and yet eventually
evolve into a highly diverse environment.

It's also worth keeping in mind that in fact, life on Earth did not
evolve much until quite recently in geological terms.  For 80% of its
tenure life was restricted to the simplest forms.  Something happened
then and we had an explosion of multicellular diversity, leading to
colonization of the land and air.  This argues against an ID hypothesis
for biogenesis, because it is unlikely that an ID would seed the planet
with a life form so limited that it would be unable to evolve diversity
for three billion years.  An ID would probably rather see immediate and
more certain results, in my opinion.

Hal