Re: Cost of natural selection revisited

Graham Jones wrote:
Selection intensity is the log of (children born) / (children that
survive). For a species to maintain its numbers (as the simulated ones
do) two children must survive per female on average, in the long term.
The genes of females that only have 0.5 surviving children will die out.
Those that have 3 surviving children will become the norm and population
pressure will reduce the number to 2.


OK, that's clear enough, but I don't think you are using Haldane's
definition of 'selection intensity'. He defines it as log(optimum survival
rate/some other survival rate). This number directly affects how quickly
substitution happens.
True, but in this simulation these numbers will be the same, noting that
in this simulation the only cause of juvenile death is genetic fitness
or lack of it. Here, all children with the optimal genome survive;
deaths are among those with lesser genomes.
A real species would need a higher fecundity to make up for background
death rates and general bad luck.


I'm not sure how much sense it makes to compare Haldane's substitution rate
with Nunney's anyway. They are looking at quite different situations.

Actually, I think they are pretty similar. Haldane considered a
situation where an environmental change made a previously harmful
mutation beneficial, and selected it from "background count" to
"everybody". Nunney considers what happens when this process is continuous.


How are you implementing 'typically the fittest individuals mate with
each
other'?
Sort all the males by fitness; sort all the females by fitness. Match
them one-one all the way down. There will be some leftovers of one sex
or the other; these fail to find mates. Just like real life.


That's not like real life at all. You are giving the organisms supernatural
powers to determine fitness in their mates, and it is not surprising that
this speeds up substitution a lot.
Fair comment, and one way I'm thinking of investigating this is by
adding a random number to the sexual fitness before sorting. That way
you could investigate how big the random number needs to be to affect
the results. I have no idea what that random number is like in real
life, and it probably depends on which genes are varying.


I don't mean to sound too critical. You seem to have done a lot of useful
work!
Criticism is the lifeblood of science :). I'm waiting for someone to
point out that this is old news (see paper A) and/or thoroughly refuted
(see paper B).

Andrew


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