Text 85, 72 rader
Skriven 2004-09-17 16:37:00 av Erland Gadde (1:278/230)
Ärende: Kin altruism
====================


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?


Regards,

Erland Gadde
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