Erland Gadde  wrote or quoted:

> To explain altruism among animals, these critics instead propose the
> idea of "kin selection".

....and of course, reciprocal altruism.

> 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!

This bit isn't right.  Individuals are only altruistic to their relatives
if the benefits to the relatives (adjusted according to relatedness) 
outweigh the costs to themselves.

An egoist would be have *reduced* inclusive fitness - compared to the
altrust - since they would fail to make sensible investments in their
relatives when appropriate.

The egoist gene would benefit from its own effects while it was rare -
but none of the other nuclear genes would benefit - so they would act
to supress the gene causing the egoism.
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