"Brian Berns"  wrote in
message > I have read
many explanations of kin selection that are based on
> the "fact" that I share 1/2 of my genes with each of my parents and
> siblings, 1/8 of my genes with each of my first cousins, etc.
>
> I have also seen it stated many times that each human shares a
> very large fraction of his/her genes (90%? 95%? 99%? -- I forget
> the exact number) with every other human.
>
> These two claims are obviously contradictory. Can anyone resolve > this
problem for me? Thanks.
>
The technical term used is "identical by descent", which maybe doesn't help
much.

Imagine we have a new mutation which has been going for only five or six
generations and is thus still very rare. The chance of this new mutation
being in a relative is obviously given by the 1/2, 1/8 metric and not the
99% one.

The point is that every new allele starts off as just such a rare mutation,
so we use the more restricted definition of "related" when calculating
whether altruism is adaptive.
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