richard_dawkins_-_the_god_delusion

138 MM: «. o n i) !•;
the spontaneous arising of something equivalent to DNA, really
was a quite staggeringly improbable event. Suppose it was so
improbable as to occur on only one in a billion planets. A grantgiving
body would laugh at any chemist who admitted that the
chance of his proposed research succeeding was only one in a
hundred. But here we are talking about odds of one in a billion.
And yet . . . even with such absurdly long odds, life will still have
arisen on a billion planets - of which Earth, of course, is one. 69
This conclusion is so surprising, I'll say it again. If the odds of
life originating spontaneously on a planet were a billion to one
against, nevertheless that stupefyingly improbable event would still
happen on a billion planets. The chance of finding any one of those
billion life-bearing planets recalls the proverbial needle in a
haystack. But we don't have to go out of our way to find a needle
because (back to the anthropic principle) any beings capable of
looking must necessarily be sitting on one of those prodigiously
rare needles before they even start the search.
Any probability statement is made in the context of a certain
level of ignorance. If we know nothing about a planet, we may
postulate the odds of life's arising on it as, say, one in a billion. But
if we now import some new assumptions into our estimate, things
change. A particular planet may have some peculiar properties,
perhaps a special profile of element abundances in its rocks, which
shift the odds in favour of life's emerging. Some planets, in other
words, are more 'Earth-like' than others. Earth itself, of course, is
especially Earth-like! This should give encouragement to our chemists
trying to recreate the event in the lab, for it could shorten the odds
against their success. But my earlier calculation demonstrated that even
a chemical model with odds of success as low as one in a billion would
still predict that life would arise on a billion planets in the universe.
And the beauty of the anthropic principle is that it tells us, against
all intuition, that a chemical model need only predict that life will
arise on one planet in a billion billion to give us a good and entirely
satisfying explanation for the presence of life here. I do not for a
moment believe the origin of life was anywhere near so improbable
in practice. I think it is definitely worth spending money on trying
to duplicate the event in the lab and - by the same token, on SETI,
because I think it is likely that there is intelligent life elsewhere.