>
>BH>First let me say that I agree with Glenn in spirit. The probability
>>argument against abiogenesis, as usually presented, is bad bad bad :),
>>and the sooner it disappears the better. The reason its bad is not
>>because a functional protein has a chance of forming in the hypothetical
>>soup, but rather that the "chance scenario" for the origin of life
>>met its demise some thirty odd years ago. To talk about the improbability
>>of life forming purely by chance is to completely ignore all the
>>modern scenarios for the origin of life. Nobody working in the field
>>today believes in the "chance scenario", so what's the point in
>>refuting it?
>
>[...]
>
>Because it is still the official creation story of blind watchmaker
>Darwinism:
>
Well, as much as I hate it <:-I, I have to agree with a lot of
what Stephen says here. I spent a lot of time looking at the
abiogenesis literature and am convinced that what I said was
correct, the "chance scenario" for the origin of life is dead.
Remember that Bradley concludes the same:
Such improbabilities have led essentially all scientists who
work in the field to reject random, accidental aasembly or
fortuitous good luck as an explanation for how life began.
-- Bradley, p. 190 of <The Creation Hypothesis>
But yet the "chance scenario" does live on, as does the soup,
in popular level writings. For me this is an outrage.
I recall reading a piece on the origin of life in the _Smithsonian_.
At first I was delighted to find the author mention the atmosphere
"problem". Unfortunately he didn't go into the details of just
why this is a problem, (a) drop in production rate of amino acids by
at least 3 orders of magnitude (probably more like 4 or 5) (b) of
this small yield one gets essentially only Lysine. But that's OK,
I thought, at least its a start. Later in the article, the author
was summarizing the successes of research and made a comment something
like "we no longer have to wonder where the building blocks came
from .... Miller etc.". I nearly fell out of my chair. Of course
we have to wonder if the atmosphere was neutral.
What's the best course of action against this?
My objection to the probability argument is when it is used as
an argument against abiogenesis rather than against one scenario
for abiogenesis. I don't know how many times I've seen this on
talk.origins. Someone gives the probability against a cell forming
spontaneously [a calculation originally performed by Morrowitz,
BTW :)] and then concludes that abiogenesis is impossible.
However, if someone still believes in the origin of
life purely by chance in a primeval soup, then of course the
probability calculations are entirely appropriate. Note in the
post that you responded to that I was using some probability
calculations myself in an attempt to thwart Glenn's attempted
rescuscitation of the chance scenario.
I think I should also try to clarify a point here. When I say
"chance scenario" I mean a scenario involving the chance formation
of something like a protein in a primeval soup. Most modern views
on the origin of life still contain an element of chance. The idea
being to reduce the amount of chance necessary to get things going.
In the RNA world, for example, the first RNA replicator would still
likely have to arise by chance. Perhaps this is what Dawkins
is getting at when he keeps asking this question "how much luck
do we need?" over and over ;-). To get a short RNA replicator
would require less luck than getting a funtional protein, presumably
anyway. As indicated previously, its not quite as simple as this
due to the so-called "error catastrophe".
I think that Dawkins and other ultra-Darwinians would like,
for metaphysical reasons, to have as much chance as possible
without it being too lucky (i.e. without it looking too much
like a miracle).
The self-orgs, however, are trying to remove luck altogether.
Stuart Kauffman would like very much to show that the origin
of life has a probability near 1, i.e. that it was for all
practical purposes inevitable. I think Dawkins would be very
uncomfortable with this.
Anyway, I think the way to handle the portrayal of the origin
of life at the popular level is to learn what the literature
really says soas to be able to answer with the facts.
I'll illustrate with some replies to Dawkins:
>"We can accept a certain amount of luck in our explanations, but not
>too much. The question is, how much? The immensity of geological
>time entitles us to postulate more improbable coincidences than a
>court of law would allow but, even so, there are limits.
according to Miller, the allowable time for the origin of life
is probably 10 million years or less. I think somewhere Dawkins
gives the old number of a billion years. Hey, he's only off by
two orders of magnitude.
[...]
>..So, there are some levels of sheer luck, not only too great for
>puny human imaginations, but too great to be allowed in our
>hard-headed calculations about the origin of life. But, to repeat the
>question, how great a level of luck, how much of a miracle, are we
>allowed to postulate?...The answer to our question - of how much luck
>we are allowed to postulate - depends upon whether our planet is the
>only one that has life, or whether life abounds all around the
>universe....There are probably at least 10^20 (i.e. 100 billion
>billion) roughly suitable planets in the universe.
>
A good answer to this is some of the fine tuning anthropic principle
stuff. Its hard to justify anything more optimistic than "There are
probably at least 10^0 (i.e. 1) roughly suitable planets in the
universe." ;-)
>..It is entirely possible that our backwater of a planet is literally
>the only one that has ever borne life....If the origin of life is such
>an improbable event that it happened on only one planet in the
>universe, then our planet has to be that planet.
>
Ah, the weak anthropic principle.
>..Our question was, how much luck are we allowed to assume in a
>theory of the origin of life on Earth?...Begin by giving a name to the
>probability, however low it is, that life will originate on any
>randomly designated planet of some particular type. Call this number
>the spontaneous generation probability or SGP. It is the SGP that we
>shall arrive at if we sit down with our chemistry textbooks, or strike
>sparks through plausible mixtures of atmospheric gases in our
>laboratory, and calculate the odds of replicating molecules springing
>spontaneously into existence in a typical planetary atmosphere.
>Suppose that our best guess of the SGP is some very very small number,
>say one in a billion....if we assume, as we are perfectly entitled to
>do for the sake of argument, that life has originated only once in the
>universe, it follows that we are allowed to postulate a very large
>amount of luck in a theory, because there are so many planets in the
>universe where life could have originated.
Dawkins states what is in fact pure speculation as if it were a
fact.
> If, as one estimate has
>it, there are 100 billion billion planets, this is 100 billion times
>greater than even the very low SGP that we postulated. To conclude
>this argument, the maximum amount of luck that we are allowed to
>assume, before we reject a particular theory of the origin of life,
>has odds of one in N, where N is the number of suitable planets in the
>universe. There is a lot hidden in that word 'suitable', but let us
>put an upper limit of 1 in 100 billion billion for the maximum amount
>of luck that this argument entitles us to assume
>
>...We go to a chemist and say...fill your head with formulae, and
>your flasks with methane and ammonia and hydrogen and carbon dioxide
>and all the other gases that a primeval nonliving planet can be
>expected to have;
I guess Dawkins hasn't heard the good news yet about the Earth's
early atmosphere. :-).
>cook them all up together; pass strokes of lightning
>through your simulated atmospheres,
yes let's do, and if we use the right atmosphere, we'll get a
yield of about 0.01% amino acids, almost all Lysine. ;-)
>and strokes of inspiration through
>your brain; bring all your clever chemist's methods to bear, and give
>us your best chemist's estimate of the probability that a typical
>planet will spontaneously generate a self-replicating molecule. Or,
>to put it another way, how long would we have to wait before random
>chemical events on the planet, random thermal jostling of atoms and
>molecules, resulted in a self- replicating molecule?...we'd have to
>wait a long time by the standards of a human lifetime, but perhaps not
>all that long by the standards of cosmological time....even if the
>chemist said that we'd have to wait for a 'miracle', have to wait a
>billion billion years - far longer than the universe has existed, we
>can still accept this verdict with equanimity. There are probably
>more than a billion billion available planets in the universe.
probably not.
> If
>each of them lasts as long as Earth, that gives us about a billion
>billion billion planet-years to play with. That will do nicely! A
>miracle is translated into practical politics by a multiplication
>sum."
>
>(Dawkins R., "The Blind Watchmaker", Penguin: London, 1991, p139-145)
>
Hey, I feel a lot better now, I've always wanted to talk back to
Dawkins. :-)
========================
Brian Harper |
Associate Professor | "It is not certain that all is uncertain,
Applied Mechanics | to the glory of skepticism" -- Pascal
Ohio State University |
========================