[Dragaera] Breaking the Cycle - Genetic Purity

[Maximilian Wilson]

On 8/28/06, Gaertk at aol.com <Gaertk at aol.com> wrote:
> "Maximilian Wilson" <wilson.max at gmail.com> writes:
>
> >[Cochran's idea is that if you take evolution seriously, not many
> >diseases can be genetic in origin because they'd quickly get bred out
> >of the gene pool; therefore we should be looking for environmental
> >causes like pathogens, which are transmitted independently of host DNA
> >and therefore not subject to evolutionary pressure in the same way.]
>
> That only works if the disease is the sort that would prevent you
> from reproducing.  My parents lived 60+ years and had three kids
> before finding out Dad was born with a defective heart valve and Mom
> had a cyst growing in her brain.


Well, it only has to have an effect on reproductive fitness. Even if a
defective heart valve is fatal in early childhood only 1% of the time,
or a cyst in the brain makes you only slightly less likely to provide
well for your offspring, over 1000 generations it will get bred out
fairly quickly, and therefore cannot be purely genetic in origin. Or
so one would expect. And sometimes one would be right:

"Although this sounds like science fiction, it is a logical outcome of
how natural selection leads to effective strategies for parasites to
get from host to host, said Lafferty. Toxoplasma gondii is a parasite
of cats, both domestic and wild. While modern humans are a dead-end
host for the parasite, Toxoplasma appears to manipulate personality by
the same adaptations that normally help it complete its life cycle.
The typical journey of the parasite involves a cat and its prey,
starting as eggs shed in an infected cat's feces, inadvertently eaten
by a warm-blooded animal, such as a rat. The infected rat's behavior
alters so that it becomes more active, less cautious and more likely
to be eaten by a cat, where the parasite completes its life cycle.
Many other warm-blooded vertebrates may be infected by this pathogen.
After producing usually mild flu-like symptoms in humans, the parasite
tends to remain in a dormant state in the brain and other tissues."

It forms cysts in the brain, which have been linked (in one study) to
an increased incidence of neuroticism in humans.

http://www.eurekalert.org/pub_releases/2006-08/uoc--cpm080206.php
http://www.livescience.com/othernews/060803_tgondii_culture.html

ObBrust: Yendi-ism could work like Toxoplasma gondii, if you go for
the cuckoo theory.

-Maximilian

-- 
Be pretty if you are,
Be witty if you can,
But be cheerful if it kills you.