Text 99, 91 rader
Skriven 2004-09-18 16:52:00 av William Morse (1:278/230)
Ärende: Re: Kin altruism
========================


erland@bredband.net (Erland Gadde) wrote in news:cif7va$19p3$1
@darwin.ediacara.org:

> The idea of "group selection" as an explanation of altruism among
> animals is discredited today among leading evolutionists. This is the
> idea that some altruist behaviour is selected because it's beneficial
> for the group (e.g. the entire species) the animal belongs to. The
> argument against this goes as follows:
> 
> "It is true that a group whose members act altruistically against each
> other might have better chances of survival in the long run than a
> competing group whose members act egoistically against each other. But
> this altruist group won't be genetically stable. As soon as a gene for
> egoism (as a opposed to a gene for altruism) appears in some
> individual, this individual will benefit from the altruism from the
> other group members (who have the altruist gene) and save the cost of
> its own altruism against others. This individual will then have an
> advantage over the other, altruist, group members and produce more
> offspring than they, and this offspring will have the same advantage,
> etc., eventually leading to that the altruism gene becomes outcompeted
> by the egoism gene. Thus, the altruist group will eventually evolve
> into an egoist group."
> 
> To explain altruism among animals, these critics instead propose the
> idea of "kin selection". This means that animals act altruistically
> only against their kin, and more so the closer they are related. The
> reason is that kin, in part, share the same genes, so a gene for "kin
> altruism" might be spread in more copies than a gene for egoism, since
> the loss of gene copies spread to the kin altruist individual's
> offspring, for acting altuistically against kin, might be less than
> the gain in kin altruism gene copies spread to the offspring of the
> individuals benefitting from the kin altruism. This will then lead to
> that the kin altruism gene will be spread in more copies than the
> egoism gene.
> 
> But does this argument really hold? As I see it, kin selection suffers
> from the same weakness as does group selection. For what will happen
> when all the indivduals in the group are kin altruists? This group
> will also be genetically unstable! If, in this group, a gene for
> egoism appears in a single individual, (after a mutation, say) this
> individual will benefit from the altruism of its kin (who didn't get
> the egoism gene), and save the cost of acting altruistically agaist
> its kin. This individual will then get more offspring (with the egoism
> gene) than its kin altruist kin and other (kin altruist) members of
> the group. The egoism gene will therefore, in the long run, outcompete
> the kin altruism gene, ust as it outcompeted the pure altruism gene in
> the previous scenario!
> 
> Or have I overlooked something? After the egoism gene has been spread
> for a few generations, the kin of the individuals bearing the egoism
> gene will also bear that gene, and these individuals then will have no
> kin altruist kin to benefit from. This will give this subgroup
> (family) a disadvantage against other families in the group who
> haven't yet been infected by the egoism gene, and still are kin
> altruists. At this stage, the relative frequency of the egoism gene
> will decrease again. It seems that finally, an equilibrium should be
> reached, where some individuals are  kin altruists and some other are
> egoists, with a stable relative frequencies for these genes during the
> following generations...
> 
> Well, these aren't easy matters. What do you think?

Congratulations! You have just successfully rediscovered the idea of an 
Evolutionary Stable Strategy (ESS), pioneered (I think) by John Maynard 
Smith and discussed by Richard Dawkins in several of his popular works on 
evolution. I do not mean to be flip - I have successfully rediscovered much 
more obvious and basic ideas on several occasions, always after 
considerable thought on my part and considerable reading of the literature. 
If you in fact recognized the possibility of a stable equilibrium between 
competing altruistic and egoistic strategies on your own, you may have a 
great future as an evolutionary theorist.

And to try to further your understanding, the importance of kin selection 
itself is a matter of debate - at best it is probably only a way of 
starting species on the path to altruism, except among the haplodiploid 
social insects.  Reciprocal altruism is probably much more important among 
mammals and birds in maintaining altruism - and in these cases the 
"egoist" is punished.

Yours,

Bill Morse
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