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


"Guy Hoelzer" <hoelzer@xxxxxxx> wrote in message news:dmgj6n$2dlp$1@xxxxxxxxxxxxxxxxxxxxxx
> in article dm5vmk$llp$1@xxxxxxxxxxxxxxxxxxx, Perplexed in Peoria at
> jimmenegay@xxxxxxxxxxxxx wrote on 11/24/05 7:16 PM:
>
> > "William Morse" <wdmorse@xxxxxxxxxxxx> wrote in message
> > news:dm4vnr$8j2$1@xxxxxxxxxxxxxxxxxxxxxx
> >> 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.
> >
> > Hooray!!!
> >
> >> 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.
> >
> > I agree. For classical group selection, in which groups DO reproduce, I
> > don't think that Guy comparison to sexual gene flow at the individual
> > level is a good one.
>
> Make your case. I feel pretty confident about my argument here.

Bill Morse already made the case that the analogy is flawed. There is
no gene flow between individuals in sex. That would require a virus vector.
But gene flow between groups (due to migration and/or outbreeding) takes
place during the life of the group.

To have an exact analogy between sex in individual selection and something
in group selection, you would have to postulate that your groups form by
a process consisting of a kind of budding (of a group 'gamete' from the
parent group) followed by a process of fusion (of two 'gametes' from
different parents).

> Dawkins
> makes the same point in arguing that selection cannot work well at the level
> of the individual. Dawkins and I simply draw nearly opposite conclusions
> from the same observation. He argues that selection cannot manifest
> effectively at the level of the individual organism, because they are not
> isolated from genetic recombination (gene flow in my argument). I argue
> that selection works just fine at the level of the individual in sexual
> populations, and that this illustrates the lack of a requirement for genetic
> isolation in the manifestation of natural selection.

Actually, I am not so sure that pure 'individual selection' does work
fine in sexual populations. If you read carefully what Edser writes,
you may conclude, as I have, that the root of his opposition to HR
is that he tries to transfer too many of the lessons of asexual individual
selection to the sexual case. Hence his r^e, etc.

> >> 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?
> >
> > In classical group selection, groups reproduce, and hence they are a unit
> > of selection. In Price or 'trait group' formulations of group selection,
> > groups do not necessarily reproduce and the individual remains the unit of
> > selection. In these formulations, groups are units of fitness calculation,
> > but once a group fitness is established, it is then bestowed upon the member
> > individuals as an element of their own reproductive success.
>
> The bestowing part of this model is a misleading and unnecessary factor,
> IMHO.

'Bestowing' was perhaps a poor choice of words. My main point was that
the ultimate truth is individual fitness, but that a portion of each
individual's fitness is derived from a group fitness.

> This model also makes another assumption that I feel is misleading
> and unnecessary; that is the notion that the identity of a group depends on
> the identities of its components.

Hmmmm. I think I see what you mean, though I would not necessarily have
used those words to describe it. But, yes, it is difficult to model
the migration of one individual from one group to another in the Price
formalism or in the Wilson formalism.

> We don't impose this assumption when
> considering natural selection at the level of the individual organism or
> below. You, for example, have essentially none of the cells of which you
> were comprised when you were born (let alone at conception). Does that
> meant that selection can't work at the individual level for humans?

No, it just means that a different model is called for to handle this
situation as a 'group selection' example. But it seems to me that there
is not necessarily a problem of defining the group as a set of individuals
in this case. Price and Wilson only require that the partition of the
individuals into groups be clear-cut. The set of cells in my body is
finite, and I doubt that there is much confusion as to which body they
belong to. I may be wrong, but I don't think that the fact that some
of my cells are descended from other of my cells is a problem.

> It
> appears to me to be something that gets imposed in the consideration of
> group selection as a sort of straw man helping us to reject an uncomfortable
> idea.

I don't think that Wilson or Price meant to construct a straw man. They
sought to revivify the notion of group selection.

> > It is my impression that the entity that evolves in either kind of group
> > selection is the species. In classical group selection, this is because
> > the species can be seen as a collection of groups, and the groups are
> > variously successful or unsuccessful. In the more modern forms of group
> > selection, the species evolves because it is composed of individuals and
> > individuals remain the unit of selection.
>
> I agree with you that SOME modern group selection models are like this. But
> I would disagree that all (most?) are this way.

Agreed.

> >> 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?
> >
> > Well, if we want to apply the Price approach to this problem, we can make
> > it work. However, as Edser is fond of pointing out, we must somehow define
> > the 'generation' as an organism generation, rather than a cell generation.
> >
> >> 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).
> >> 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.
> >
> > Which means that a single individual or single pair is the ultimate
> > recipient of all altruism. Which means that Hamilton's IBD 'r' is going
> > to be involved, perhaps in addition to various group-selective metrics.
> >
> >> 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. Those
> >> species in which, for whatever reason, individual selection creates
> >> traits that benefit groups, will survive in preference to other species.
> >
> > I am skeptical about 'good of the species' as long as it is the species
> > that is evolving. But I am quite willing to consider traits that are
> > for 'the good of the group', even if it is difficult to identify a benefit
> > to any individual. I strongly suspect that such traits are traits that
> > are 'emergent' at the group level - that is, they can not be attributed
> > to individuals. As examples of such traits, we might have various kinds
> > of balanced polymorphisms or perhaps mating protocols (which involve at
> > least two individuals).
>
> I agree that it can help to keep the arguments more clear by focusing on
> traits that emerge at the group level (e.g., group size, social
> structure...). However, I wouldn't restrict the notion of selection to such
> traits. This way of thinking about selection would, for example, preclude
> the conclusion that individual selection influences the DNA sequences of
> genes.

I disagree. You seem to be suggesting that the rules must be identical
in going between any two levels of a hierarchy. But, the way that groups are
composed of individuals is entirely different from the way that individuals
are 'composed of' genes. You can't necessarily carry a lesson from one
level to another level.


.

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