Re: Hamilton's rule

Guy Hoelzer (hoelzer@xxxxxxx) writes:
> in article dj1v9g$1p6k$1@xxxxxxxxxxxxxxxxxxx, Perplexed in Peoria at
> jimmenegay@xxxxxxxxxxxxx wrote on 10/17/05 9:56 PM:
> As we know from Ohta's Nearly
> Neutral Theory, very weak selection pressure is virtually the same as no
> selection pressure at all, leaving alternative alleles free to drift.

(A)
Only if it's really extremely weak. Suppose it's so weak that
in the time it would normally take for genetic drift to wipe out
a gene that started as being in half of a large population, the
weak selection pressure only increases the number of individuals
with the gene by 1. Well! The gene has just greatly increased
its chance of survival, then, hasn't it? Instead of being
completely wiped out, there's still this one individual with
it. It would then have something like a 50% chance of
soon getting completely lost, and a 50% chance of continuing,
with perhaps about as much chance of taking over the whole
population by genetic drift as of being wiped out later.

I consider weak selection pressure to be a very important
factor in evolution. To put it another way: you can neglect
it if you choose to, but I find it quite interesting.

> My
> contention is that the extent of kin selection pressure (the strength of kin
> selection) becomes very weak as the altruism allele becomes common.

(B)
I disagree. Even if 99.99% of the population has the altruism
gene, the individuals who do not have it face a quite significant
probability that their siblings and close relatives don't have
it either: something on the order of 0.5, 0.25 etc., not 0.0001.
This lack of the gene in their siblings can then provide quite a
considerable impact on the fitness of those individuals
without the gene, causing considerable selection pressure against
individuals without the gene.

> In
> fact, I think it would typically become negligible even at intermediate
> frequencies of the altruism allele (say above 20 or 30%).

I completely disagree (see two arguments above).

> To be clear, the validity of the kin selection model is NOT dependent on
> allele frequencies, however the influence of kin selection over the
> evolutionary process IS dependent on allele frequencies. I am not arguing
> that kin selection is an example of a frequency dependent selection model.

To be honest, I don't understand the above paragraph at all.

>> Or are you saying that 'rb>c' remains valid in determining the direction
>> of the evolutionary force, regardless of frequency, but that the
>> magnitude of the force depends upon frequency? If that is your position
>> then I apologize unconditionally.
>
> Oops. I should have read this first. This is indeed my position.
>
> Guy Hoelzer

I would need a quantifiable definition of "evolutionary force"
before I could decide whether I agree with the above.
I suspect I disagree with it (see my argument labelled "(B)" above).
--
Cathy Woodgold
http://www.ncf.ca/~an588/par_home.html
We are all Iraqis now.

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