Re: Most important paper in evolutionary biology
- From: "Perplexed in Peoria" <jimmenegay@xxxxxxxxxxxxx>
- Date: Thu, 22 Sep 2005 17:25:02 -0400 (EDT)
"aj" <aj@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message news:dgst1d$tat$1@xxxxxxxxxxxxxxxxxxxxxx
> In article <dgpit7$2mgg$1@xxxxxxxxxxxxxxxxxxx>, Perplexed in Peoria
> <jimmenegay@xxxxxxxxxxxxx> wrote:
>
> > I think that the heart of your confusion is an important distinction in
> > the definition of OFA. I will offer two definitions of OFA. Under one
> > of these definitions, I will agree that Darwin and Wallace would say that
> > it is prohibited - that it can't evolve. The thing is, I claim that
> > Hamilton would agree with them. He would also say that that kind of OFA
> > can't evolve.
> >
> > But there is another kind of OFA (a second definition) which Hamilton would
> > say can evolve. I claim that Darwin and Wallace never really thought about
> > this kind of OFA (except maybe as applied to parental care). But if they
> > had thought of it, they would agree with Hamilton.
> >
> > Here is the first definition:
> > A gene is said to cause OFA if, on average, having the gene decreases
> > the fitness of the bearer (called the donor), and increases the fitness
> > of some other individual (called the recipient).
> >
> > I suppose we need to define fitness here - I am happy to accept your
> > usual definition of TDF.
> >
> > I suppose I also have to defend those words 'on average'. I put them there
> > because sometimes organisms do really stupid things. The important issue
> > for evolution is not whether an organism ALWAYS acts to maximize its TDF -
> > it is whether its traits tend to increase TDF on average.
> >
> > Ok, given this definition, does Hamilton say that OFA can evolve? I claim
> > he does not. It is pretty much obvious that a gene causing OFA using
> > this definition is headed for extinction. The gene has no way of getting
> > into the next generation except by its bearers having fertile offspring,
> > and the OFA gene BY DEFINITION causes its bearers to have fewer children
> > on average. Hamilton was not stupid enough to say that this gene could
> > be favored by evolution. Obviously, it can't.
> >
> > Alright, here is the second definition:
> > A gene is said to cause OFA if it causes a behavior which, on average,
> > decreases the fitness of the bearer (called the actor or donor), and
> > increases the fitness of some other individual (called the recipient).
> >
> > Hamilton says that OFA, under this definition, can be favored by selection
> > under some circumstances. The right circumstances are when rb>c.
> > The reason why this kind of OFA can increase is that bearers also
> > have their fitnesses increased by the behaviors of other bearers.
> > But if you are using definition #1, you wouldn't count this situation
> > as OFA. You would call it OFM.
> >
>
>
> I'm having trouble following your argument, and was wondering whether
> you could clarify it. As I understand it, the gains to inclusive
> fitness under kin selection in no way depend upon the original donor
> subsequently becoming a recipient.
That is correct. Nor does it require that the donor have been a recipient
BEFORE becoming a donor. Before is the more likely case, but neither
is absolutely required.
> In fact, the donor's inclusive
> fitness can increase if the first time it exhibits the behavior, such
> behavior causes its death.
That is also correct.
> The only condition that necessary is that rb>c.
> This being the case, I don't see a difference in your two
> definitions. The only difference appears to be that you've added
> "causes a behavior" to the second definition, but in the first
> definition, as long as rb>c, the result is the same.
>
> Perhaps I'm missing something here; I'd be grateful if you pointed it
> out.
Well, the main thing that you seem to be missing is the distinction between
bearers of the gene and donors. The donor's ACTION increases his *inclusive*
fitness if (on average) he is helping other bearers of the gene more than
he is himself being hurt. And also proportionately more than he is helping
non-bearers. But that means that, averaged over the entire population,
bearers are both giving and receiving. Non-bearers only receive, but they
receive less frequently than do bearers. When you do the math, you will
see that if rb>c, the bearers get more net benefit from the altruism than
the gross benefit received by non-bearers.
Your example where the donor dies if he acts altruistically can be made to
work, if b is particularly large. But it can't be made to work if EVERY
organism that bears the gene acts altruistically and dies childless. You
need some bearers of the gene that don't express the extreme altruism.
For example, the queen bee carries the same altruistic 'gene for sterility
in workers' that the workers do. But she doesn't express it, and she receives
enough of a benefit from her altruistic daughters and siblings to make up
for their sacrifices. The average bearer of the gene (including the queen
in the calculation of the average) does very well from this arrangement.
Having the gene does not, on average, decrease the fitness of the bearer.
It may bring with it the burden of acting altruistically, but it also tends
to appear mostly in those 'lucky' individuals who are born with lots of
helpful relatives.
.
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- Re: Most important paper in evolutionary biology
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- Re: Most important paper in evolutionary biology
- From: Perplexed in Peoria
- Re: Most important paper in evolutionary biology
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