Re: A question about the theory of Kin Selection

On or about Fri, 20 Jun 2008 03:51:36 -0700 (PDT) did Kippers
<robin@xxxxxxxxxxxxxxxxxxxxxxxxx> dribble thusly:

There is something I don?t understand about this idea which I hope
someone can explain to me. I think my confusion comes from the
explanation of how genes are passed on by sexually reproducing
organisms.

As I understand it offspring of a sexually reproducing couple receive
50% of each parents DNA but surely this cannot equate to the offspring
having just 50% of the genes of each parent given that each parents
genome will contain more than 50% of the genes of the other parent.

Would I be correct in thinking that the offspring of a sexually
reproducing couple would actually contain more than 99% of the genes
of each parent even though it inherits 50% of the DNA from each
parent?

Forget quantity of genes. Think probability.

For any given gene, there's a base probability that it will be in any random
organism of the gene pool. Some genes are fixed species-wide, making that
base probability 100%. That makes such a gene irrelevant for evolution, since
there are no different options to select (not that a fixed gene can't cause
extinction, eventually).

Others have lower base probabilities, going right down to 0% for a brand new
mutation never before seen.

The relatedness figures represent the probability above and beyond the base
probability.

So when you say the gene in a child has a 50% chance of being in either
parent, you're saying 50% over and above the baseline chance of it being in
any random human.

Another reason to use the language of probability is that it helps make clear
that there's nothing special about actual descendants. Grandparents have a
25% degree of relatedness with grandchildren, from their direct gene
contributions. But aunts and uncles, despite not donating any DNA, also have
a 25% degree of relatedness. And let's not forget that full siblings are at
50%, just like parents and children.

So long as there are other alleles in the gene pool, that gene can potentially
increase in frequency from behavior that benefits close kin as well as the
immediate host organism.

There's nothing special about parent/offspring relatedness beyond the fact
that it's much easier for an organism to "know" its degree of relatedness (if
it's the mother, anyway - the mother's brother is often more nurturing than
the putative father, since a solid 25% is sometimes better than from 0% to
50%).

The upshot is, if the probability of a gene being in another organism is 100%,
there's no benefit (in the form of a higher frequency in the gene pool) for a
gene to gain by being altruistic. That's why your cabbage doesn't make the
grade.

.

Relevant Pages

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