Re: virus: What makes memes compete?

Lee Daniel Crocker (
Fri, 11 Apr 1997 16:01:27 -0700 (PDT)

> Tim Rhodes wrote:
> > is in the interest of your genes
> >to protect your brother until the risk is greater than 50-50 that you,
> >yourself, will die (for half of your genes can survive through him).
> Rubbish! This is one of the most common "scientific" canards.
> How many genes do siblings share? Well, I'm led to believe
> that humans and chimpanzees share about 98%. Just think
> about it, OK?

Think about it more clearly: percentage of shared DNA is irrelevant.
It makes the mistaken assumption of equating "genes" with their
physical expression. Genes are the words, not the paper. A piece
of DNA at the same locus on the same chromosome and the same coding
sequence in a human and a chimp are not the same gene, because that
human gene has no power to affect the chances of success of its
sister in the chimp. And at any rate, a selfish gene cares not
about any other gene in the whole set when it comes to altruism--
it cares only about the probability of itself existing in the other.

What happens over evolutionary time is that genes whose influence
on their hosts cause them to more successfully replicate those
genes are the ones who find themselves in the next generation. But
it is only when there are two or more alternatives that such selection
is even possible. A gene that is the same in every member of a
species cannot evolve until a mutation occurs to cause differential
selection. When that happens, the success of that gene will depend
upon the effect it has on its host's success. Let's say that the
mutant caused a behavioral difference: the "normal" gene at that
locus caused a behavior that would make you sacrifice your life for
one child; the mutant made you more reluctant, and so you'd only
sacrifice your life for two children. Which gene is likely to find
itself in future generations? Set up the computer simulation and
watch. The mutant will spread, because those with the new gene will
not sacrifice themselves for a single child that has a 50% chance
of having its allele, but those with the old gene will. The gene
closer to 50% will always spread better than any allele that might
come up with a different percentage.

Of course, that's a simplicifcation, because you really have to
count the amount of parental resources invested in each child, and
the reproductive chances of the child matter as well. But as a
general approximation, the amount of altruism one should give to
a cospecific from any one gene's point of view is proportional to
the odds of that gene--and only that same gene with the same
effects--being in the other organism. Whatever other genes might
be shared are completely irrelevant. A final complication is your
ability to estimate those odds. In a species like Bonobos, who
have sex more than they eat, a father has no idea which children
might be his, so Bonobo males tend to care for their siblings and
for their sister's children, who they know share their genes, but
have no interest in the chilren of those they mate with.

Lee Daniel Crocker <>  <>
"All inventions or works of authorship original to me, herein and past,
are placed irrevocably in the public domain, and may be used or modified
for any purpose, without permission, attribution, or notification."--LDC