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Topic: Several questions on evolution, and mutation (rate)
Replies: 52   Last Post: Sep 8, 1996 9:44 PM

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 Mary K. Kuhner Posts: 1 Registered: 12/12/04
Re: Several questions on evolution, and mutation (rate)
Posted: Aug 22, 1996 5:46 PM

In article <Pine.A32.3.91.960815144016.39360B-100000@flute.aix.calpoly.edu> Andrew Singer <asinger@flute.aix.calpoly.edu> writes:
> "..the mathematician D.S. Ulam argued that it was highly
>improbable that the eye could have evolved by the accumulation of small
>mutations, because the number of mutations would have to be so large and
>the time available was not nearly long enough for them to appear..."

>1- How does someone determine how long it would take for a series of
>mutations to occur (all being presumably favorable mutations)?

In my opinion we are nowhere near being able to pose this question for a
structure such as the vertebrate eye. How many mutations *does* it take
to make an eye? It depends, critically, on how much of the code was
created more or less *de novo* and how much was cribbed from other
applications. If a lot of the stuff needed to make an eye is already
implicit in the genome, serving other functions, you might be able to
make an eye very easily indeed. Need a muscle to focus the lens? Just
tweak the muscle that closes the eyelid.

To know how probable the eye is, we would have to know how many
different ways you could use a reasonable number of mutations to
adapt the pre-existing code into an eye. But since we don't know
how many ways there are to make an eye (at least three, as another
poster points out) or what the details of the pre-existing code were,
there is no way to make a meaningful probability estimate.

You could get a start by identifying all the eye genes, and then asking
where they seemed to have come from--do they have close relatives in
other systems, or are they new genes? How different are they from their
neighbors? We have not done this yet, except for a very few genes.
The genes that make human red-detecting and green-detecting pigment
are siblings--about half a dozen mutations were needed to change from
bichromatic to trichromatic vision. But eyes are old, and some of the
evidence may be lost in history.

It's also worth noting that not all successful mutations are favorable
mutations; many mutations occur and persist by chance because they are
not harmful, or not too harmful. I suspect that the genetic quirk which
makes my lineage blonde as children and brunette as adults has no
use at the moment, but it's available for subsequent mutations that
would *give* it a use (for example, the control sequences that let the
hair-color gene tell a child from an adult could be attached to
something else).

In my opinion we cannot make meaningful estimates of the probability
of evolution for any complex structure, much less all of life; we
just don't know enough. We certainly can't say with any confidence that
it was too improbable to happen.

Followups might well go to talk.origins.

Mary Kuhner mkkuhner@genetics.washington.edu

Date Subject Author
8/15/96 Andrew Singer
8/16/96 Lluis Ribas
8/16/96 Doug Yanega
8/17/96 Leonard Evens
8/16/96 KIRKX L AUGUSTIN
8/17/96 Leonard Evens
8/28/96 Brian Williams
8/29/96 Lauren Owens
8/18/96 Felix J. Thibault
8/20/96 Vincent R. Johns
8/23/96 Richard M Kliman
8/25/96 David Beorn
8/26/96 Vincent R. Johns
8/27/96 Steve McGrew
8/27/96 James Foster
8/29/96 David Beorn
8/30/96 James Foster
8/31/96 L.A. Moran
9/3/96 James Foster
9/4/96 L.A. Moran
9/4/96 James Foster
9/4/96 Ram Samudrala
9/4/96 James Foster
9/4/96 Ram Samudrala
9/5/96 James Foster
9/5/96 Ram Samudrala
9/6/96 James Foster
8/27/96 Joan Shields
8/28/96 Steve McGrew
8/29/96 David Beorn
8/30/96 Jerry Learn
8/31/96 Doug Easton
8/30/96 Larry Edwards
8/30/96 Doug Yanega
9/7/96 David Beorn
8/27/96 David Dixon
8/28/96 Dana Gourley
8/30/96 Herman Helmuth
9/6/96 Jerry Clark
8/22/96 Truett L Smith
8/28/96 Brian Williams
8/23/96 Karl
8/24/96 Steve McGrew
8/25/96 Arthur Chandler
8/21/96 vorsterd@iafrica.com
8/22/96 Anthony Campbell
8/22/96 Mary K. Kuhner
8/31/96 Arthur Chandler
9/4/96 David Wilson
9/6/96 Ram Samudrala
9/8/96 David Wilson