Re: Group selected altruism - (was: Hamilton's rule)

in article dm4vnr$8j2$1@xxxxxxxxxxxxxxxxxxx, William Morse at
wdmorse@xxxxxxxxxxxx wrote on 11/24/05 10:11 AM:

> Guy Hoelzer <hoelzer@xxxxxxx> wrote in
> news:dm0r0a$1fmf$1@xxxxxxxxxxxxxxxxxxx:
>
>> in article dlvnf0$mco$1@xxxxxxxxxxxxxxxxxxx, Jim McGinn at
>> jimmcginn@xxxxxxxxx wrote on 11/22/05 10:19 AM:
>>
>>> All that is necessary for group selection is that there situational
>>> factors that prevent or reduce gene flow between groups, as Catherine
>>> described, and situational factors that cause differential
>>> survival/reproduction between the groups, as Catherine also
>>> described.
>>
>> Jim,
>>
>> I am surprised that you of all people have advocated an unrealistic
>> constraint on the potential for group selection. What difference
>> could it possibly make to group selection to "prevent or reduce gene
>> flow between groups"? Isn't that analogous to arguing that it is
>> necessary for individual selection that gene flow between individuals
>> (sex) is prevented or reduced? IMHO, gene flow is utterly irrelevant
>> in both instances.
>>
>> Guy
>>
>>
>
> Well perhaps it is time to stop flogging Hamilton's rule and start
> flogging the unit of selection again.

Thanks Bill. That is a much more interesting topic IMHO.

> The analogy between individuals and groups will not be exact, but let's
> look at it. If we limit our discussion to eukaryotes, gene flow between
> individuals does not occur _during the lifespan of the individual_. It
> only occurs when the individual reproduces. So if we are trying to make
> group selection an analog of individual selection, then we should not
> expect gene flow between groups until the groups reproduce. The analogy
> should work if groups do tend to reproduce - but do they? In this groups
> are perhaps more like species, which may give rise to other species but
> do not per se reproduce. But the standard view is that individuals
> reproduce, it is species that evolve - Dawkins perhaps would say the
> genes reproduce and species evolve. So where do groups fit in to this? Do
> they evolve or reproduce, or both, or neither?

A species is just one kind of group composed of individual organisms, so
anything said about group selection MUST apply to selection at the level of
species, IMHO. I also think it is safe to say that groups can both
reproduce and evolve.

> And while we are looking at analogies that may not work too well, why
> shouldn't multicellular "individuals" be looked at as groups of cells, or
> why shouldn't cells be looked at as individuals? With some exceptions, we
> typically discuss genes as the unit selection or organisms as the unit of
> selection, but we ignore cells as the unit of selection. Why is that? Yes
> in multicellular organisms most cells don't reproduce, but the germ line
> cells do. Why aren't they the unit of selection, or at least a unit of
> selection?

I agree completely that individuals at any level (e.g., individual gene
copies, individual genes, individual cells, individual organisms, individual
social groups, individual species...) ARE populations of smaller entities.
This is an important reason for at least a serious consideration of
extending Darwinian selection theory to multilevel selection theory.

> Now if we prefer the viewpoint that for multicellular organisms it is the
> individual organism that is the primary unit of selection (this is my
> personal prejudice), shouldn't we then allow that since a multicellular
> organism in in fact a group, that therefore a multiindividual group can
> be similarly selected? (I think that is Guy's and JimMcGinn's belief).

I'm happy with that statement.

> The requirements (if we are still arguing by analogy) are that a single
> individual of the group is responsible for reproducing the group as a
> whole. This is largely true of the social insects, and approximately true
> of naked mole rats. To a much rougher approximation it may be true of
> wolfpacks and a few other mammal groups.

I think you have pushed the analogy too far here, because you are too
wrapped up in mechanistic details when I think you should focus on the key
factors involved with the process. For example, it may be a single cell,
the gamete, that represents a whole organism in reproduction, but it does
not represent the whole population of organisms, which is level within which
we traditionally recognize the manifestation of evolutionary processes. If
we discovered a species tomorrow in which two gametes from each individual
contributed to fertilization, I doubt any evolutionary biologists would jump
to the conclusion that this lineage could not evolve or be the target of
natural selection. If we are to focus on the process of selection, then I
think we should be clear about the necessary and sufficient conditions for
natural selection to happen, without getting caught up in mechanistic
particulars. I would argue that natural selection happens whenever there is
heritable variation for fitness. Anything less is insufficient, and
anything more is too restrictive, IMHO.

> For most other groups (e.g. human tribal groups) there is no single
> individual that reproduces the group as a whole, and the analogy with
> individual selection is probably not particularly helpful in
> understanding whatever group selection may or may not occur. In this case
> I think Jim McGinn's argument for group selection is on rather differnt
> lines.
>
> This thought process should perhaps be followed a bit as to the question
> of evolution of traits that are "for the good of the species". Since
> selection operates on individuals but species evolve, it would seem that
> the evolution of traits that enhance species survival might still be
> expected, especially if we take into account neutral processes.

Sexual selection, the aspect of natural selection that maximizes
reproductive success as opposed to viability, can result in evolution that
puts a species at risk of extinction. This is an example illustrating that
selection does not always make the population more robust. It generates
future generations in which individuals are more fit (assuming the
environment doesn't change). [Please note that I am using the words
"individual" and "population" generically here, with the intent of covering
any level at which selection might act.] Individual selection makes for
populations of better individuals. Group selection would make for
populations of better groups. Better components of populations do not
guarantee better populations.

> Those
> species in which, for whatever reason, individual selection creates
> traits that benefit groups, will survive in preference to other species.

This would probably be true most of the time, but I don't think it would be
universally true.

Guy


.

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