Re: Haldane's Dilemma - clarifications - and Felsenstein [LONG]

Perplexed in Peoria wrote:
More interesting to me is whether unsuccessful
substitutions really impose a cost (or, to use
your terminology, whether this cost is 'limited').

You appear to be mis-using my terminology. A cost is a *requirement*
of a given evolutionary scenario. If the species cannot 'pay the
cost', then the scenario is not plausible. That is a basic cost
argument.

But cost arguments are not the ONLY arguments that limit the
substitution rate. The substitution rate is ALSO limited by
mutation-rate arguments. WHICHEVER LIMIT IS LOWER.

Briefly, the substitution rate will tend to be mutation-rate-limited in
small populations, and cost-limited in large populations. That is how
my term "limited" is used.

Since the mechanism by which unsuccessful substitutions
fail is the same random sampling error that causes some
neutral mutations to be fixed, I would think that these would
have no effect on the limit.

I will give a simple example of the cost of unsuccessful substitutions.
Keep it simple, focus on a single substitution. Suppose there is a
beneficial mutation that gives a one-percent selective advantage by
increasing the reproduction rate . Now suppose -- as ALMOST ALWAYS
occurs -- that the beneficial mutation substitutes part way, then is
overcome by genetic drift and eliminated. How does that generate a
cost of unsuccessful substitution? It is given within the scenario.
The scenario REQUIRES an increased reproduction rate (i.e., an
increased cost), even though the substitution is unsuccessful. Now
multiply that by all the unsuccessful substitutions. The requirement
exists for other scenarios too. I just gave a simple example so you can
see it.

This *requirement* -- this cost -- adds to all the other costs the
species must pay. The larger this cost, the less payment remains for
paying the other costs of evolution -- and that will slow the
substitution rate.

The amount of that cost will depend on the scenario, and on the degree
of dominance (or recessivity) of the beneficial mutation.

-- Walter ReMine
The Biotic Message
http://SaintPaulScience.com


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Relevant Pages

  • Re: The Cost of Substitution
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  • RE: The Cost of Substitution
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  • Re: Haldanes Dilemma - clarifications - and Felsenstein
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