On Fri, Apr 20, 2001 at 06:36:55PM -0400, James Tauber wrote:
> One thing that has always fascinated me is the number of genotypic mutations
> that need to take place for the phenotype to have a beneficial change. It's
> not as if a single change to the DNA has an immediate benefit. You really
> need somehow to built change-upon-change, each of which has no individual
> benefit, but the whole sequence of changes leads to a benefit. Survival of
> the fittest can't kick in until the benefit does and so a partial sequence
> of changes leading to a benefit would be have no greater chance that one
> that doesn't lead to a benefit.
>
This is pretty much an "FAQ" as far as evolutionary biology goes. The
canonical example is - how do you evolve an eye or a wing, given that "half an
eye" or "half a wing" confers no advantage until the entire mechanism is in
place?
http://www.cs.colorado.edu/~lindsay/creation/eye.html has a good summary of
standard answer. In short, it's possible to describe scenarios of transitional
features that lead to the systems we see today, and do confer individually
advantage. In the case of an eye, a set of stages that move from a
photo-sensitive "eye spot" (based on the photochemistry of single-cell
organisms), to a fully-fledged eye, have been described. Each stage confers an
advantage: the stages roughly reflect what we see in the fossil record. None
of the stages is particularly unlikely.
> James
>
> > Three decades ago, Frank Salisbury of Utah State University described the
> > odds this way: "Imagine one hundred million trillion planets, each with an
> > ocean with lots of DNA fragments that reproduce one million times per
> > second, with a mutation occurring each time. In four billion years, it
> > would still take trillions of universes to produce a single gene -- if
> > they got lucky."
>
Let's include this with the proceeding paragraph:
Hoyle's best-known analogy has a tornado in a junkyard taking all the
pieces of metal lying there and turning them into a Boeing 747. It
would be amazing, but possible, for two pieces to be naturally welded
together, and then two pieces more in a later whirlwind, but
production of even a simple organic molecule would require all of the
pieces to come together at one time.
Again, this is a pretty old objection (as John says, even Salisbury's piece,
in the American Biology Teacher is three decades old). The last thirty years
have been mostly filled by evolutionary scientists trying to explain the
misconception about the nature of chance that this argument is based upon.
Again, in a nutshell, you don't *need* to have all the pieces to come together
at one time. You just need a chain of events, each of which, *at that stage*
is not unlikely.
This is the argument that Dawkins' first book, The Blind Watchmaker, set out
to answer. He explains it a lot better than I ever could.
d.
>
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