David Leeper wrote:
> Evolution is sneakier (is that a word?) than this. It'll mutate the
> replicators and throw a new beast at the problem. If that doesn't work
> it'll try again with another beast, and another, and another.
>
> Here's the secret. Not all mutation cause a change in the phenotype
> of the replicator. Mutations occur and the beast remains at the same
> spot on the fitness landscape. But _collections_ of "useless" mutations
> can combine to create a valuable mutation (See Gould on this topic).
> This combination creates a big jump that no single mutation can do by
> itself. Evolution can continue this process ad infinitum until it finally
> gets out. Evolution never gets stuck.
Yes, it does. "Get stuck" doesn't mean stop. It doesn't that all
change ceases and organisms become static entities from an evolutionary
perspective. It means that with respect to some physiological structure
they are prevented from acheiving the optimal design because they took a
wrong evolutionary turn early on. There's no going back.Mutations have
to build on what's already there. The human eye is wired screwy the way
it is because cumulative selection built a complex light-focussing and
metering mechanism a step at a time from a much simpler light-sensitve
mechanism. For evolution to back track back to a point where random
mutation could result in a simple eye that could be built up into a
complex eye with nerves running out the back of the light sensitive
cells rather than out the front, there would have to be some selection
pressure that favored eyes that don't see very well. Each mutation that
moved our ancestors' eyes further from the simple clusters of light
sensitive cells towards the complex mechanisms our eyes have become went
from being an oddity to being the norm because it confered a survival
advantage. To trace backwards to the juncture from which reaching the
optimal eye would be possible, generation after generation would have to
have increasingly primitive eyes and increasingly poor vision as the
muttional kluges that once conferred survival value and became the norm
were stripped away. Natural selection doesn't drive evolution
backwards, only forwards. Did you read the Dolo's Law post?
I haven't read Dawkins'new book, Climbing Mount Improbable, but I know
that this is a central topic of that book. You might want to check it
out. Actually, I suspect you won't WANT to, as you have good reason to
think that Dawkins will spend several hundred pages explaining why
you've dug your heels in on the wrong side of this issue. As always, do
as you will.
-KMO