Re: Bet Hedging, Risk Aversion, Sex, and the Unit of Selection

"Perplexed in Peoria" <jimmenegay@xxxxxxxxxxxxx> wrote in
news:drgc5j$896$1@xxxxxxxxxxxxxxxxxxx: 
 
> "William Morse" <wdmorse@xxxxxxxxxxxx> wrote in message
> news:drccbo$1ko0$1@xxxxxxxxxxxxxxxxxxxxxx 

>> You will need to explain this further for me to understand your
>> argument. I would have thought that bet hedging only makes sense if
>> the unit of selection is the organism, or better yet the species. The
>> organism "tries" different combinations of genes to see which ones
>> will work out. The species maintains polymorphism so that it can
>> respond to environmental changes, even though this sacrifices some
>> individual fitness - The Selfish Gene Pool.
> 
> I agree that the species level might be the best viewpoint, and
> disagree that it makes sense at the individual level.  But here is the
> thinking behind my claim that it also makes sense at the gene clone
> level: 
> 
> Consider a sexual species with several loci with alleles A and a at
> one, B and b at another, etc.  Consider NS from the viewpoint of our
> focal allele A, which is engaged in a long term struggle for world
> domination (well, at least domination of the species) with its enemy,
> the allele a. Any individual gene (DNA molecule segment) in any
> organismic individual is merely a foot soldier in this epic struggle. 
> The antagonists are the entire A clone and the entire a clone - each
> distributed among many individuals.
> 
> For simplicity, we will assume that the species undergoes selection
> in haploid form.  Now neither A nor a care much about the environment.
> But alleles B and b DO care about the environment - in fact, each is
> adapted to a different environment.  The question is, should our
> protagonist A prefer to have its 'troops' billeted with B or b.  My
> claim is that if bet hedging makes sense in this situation, then A
> should want to have a mix of AB and Ab individual organisms.
> 
> How does A accomplish this laudable goal?  Well, it does what it can.
> It firmly opposes any conspiracy at other loci to switch individual
> reproduction from sexual to asexual.  And, it attempts to locate
> itself on a different chromosome than the B locus.
> 
> The situation is more interesting if there are epistatic interactions
> between the two loci.  Now it may be the case that it makes sense for
> A to try to be linked with the B locus on the same chromosome.  It
> may be that the AB combination is fitter than Ab.  If so, selection
> will lead to a deviation from multi-locus HW equilibrium.  And that
> deviation must be viewed as a good thing from the standpoint of a
> non-hedging optimizer who is only interested in maximizing ln(E(W)). 
> But it may not be a completely good thing from the standpoint of a bet
> hedging optimizer who is interested in maximizing E(ln W).  Hence
> recombination (which reshuffles genes in a way that LOWERS average
> individual fitness). Hence sex is useful only if the optimizer is a
> bet hedger. 

Ah So Deska! 

The problem I have always had with the selfish gene (Dawkins notes this as 
a problem himself) is explaining how to reconcile this with the ubiquitous 
honesty of meiosis. Yes there are segregation distorters, but they are 
rare, and even with the famous drosophila example there is a mitigating 
selective explanation. OTOH, there are numerous other genetic effects, e.g. 
transposons,that are easy to understand from the gene's eye view but make 
little sense at the level of the phenotype. Your argument may help me with 
the reconciliation.

Now I may still have a problem with a mechanism for A to accomplish its 
goal of maintaining sexual reproduction. I can forgive teleological speech 
for the most part, and tend to agree with Dennett in his use of "the 
intentional stance", but there are times when even though an allele might 
be at a selective advantage if it "opposes a conspiracy", there is simply 
no way it can do this, in which case the intentional stance leads us 
astray. 

But assuming there is a way, I am intrigued by your argument. 

Yours,

Bill Morse 

 

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