On 13/07/2006, at 5:44 PM, Alberto Monteiro wrote:
Charlie Bell wrote:
....example please? Of a natural diploid population with a highly
skewed male/female ratio. Haplodiploidy causes sex ratio bias, as I
discussed previously.
This ratio can come after a fierce and deadly competition among
males. Those males that are excluded are, darwinially, dead.
That a large proportion of the males might not go on to breed
actually says nothing about the sex ration in the next generation.
The ratio continues to be close to 50-50. You are theorising away
merrily, but there are in reality very few examples of skewed bias
in diploids, as I've said. If you'd like to give an example of one
you've found, we can analyse it, but I am telling you now that it's
very rare because of stabilising selection -
Ok, but competition among males creates an opportunity for
a polygamous society.
Absolutely. Harems aren't uncommon - many deer, antelopes, monkeys
and apes, cattle, and obviously lions. It is interesting that nearly
every social setup we can imagine does seem to appear - even
polyandry, most spectacularly amongst deep-sea angler fish where one
large female is "wed" to several males, who are essentially parasitic
sperm balls attached to her skin.
even in the situation
you're alluding to, it's still an advantage to females to produce
sons as well as daughters -
Not if we accept technological advances.
I'm saying that no matter the technology, it's inherently unstable,
and a perturbation, for example wild-type genes invading the
population, would be likely to cause the system to fall apart.
a skewed sex ratio will make it
advantageous to have more sons, and so equilibrium is restored. It
might be "wasteful" in terms of males, but evolution doesn't care,
it's just success that matters.
That's what must be carefully modelled before we jump to conclusions.
Intuitively, it seems that males have no advantage over lesbian
females in a society where there are as many males as heterosexual
females, and where lesbians can reproduce sexually with other
lesbians.
However, lesbians _may_ have some advantages over heterosexual
females, and this will slightly push the lesbian:hetero ratio
in the population towards a lesbian dominance.
I am still waiting for the Hardy-Weinberg equilibrium models!
Ok, I saw that, but it's specifically designed for non-sexual
genes.
It can be used to model ratios of the frequency of the sex
chromosomes, iirc, but not allelic frequencies of alleles on the sex
chromosomes.
Spoilers for those who haven't read Stephen Baxter's current trilogy,
so I'll link to Ye Olde Wikipedia again... ;)
First you need to understand eusociality - http://en.wikipedia.org/
wiki/Eusociality
Ok - I won't read it now.
I know it's not so simple. Before males appeared as a separate
subspecies, all creatures were hermaphrodites.
Or asexual.
Yes, of course. I think you could get what I intended to say :-)
A sentient species can stop evolution of itself, even if the
evolution would produce a "better" [to their sentient criteria]
species
Only by eliminating all variation (and all sources of variation), or
by only breeding through cloning vats. If there is *any* variation
at all, the *slightest* selective advantage will eventually prevail.
No - taking back to Science Fiction, did you read the "Foundation
and Robots" Trilogy? If not, I will not spoil :-)
Tell me the principle, without spoiling the story, if possible. But
what non-biologists often fail to fully appreciate is just how
powerful the selective force is.
I once saw a sf short movie where kids had to do an intelligence
test when they became teens, and the State _eliminated_ those
students that were too smart. It seems that most societies
are just doing that right now, and trying to eliminate those
members that raise above the mud of the population.
Based on a short story I have, but I can't remember the author.
Isn't this what bullies in schools systematically do?
It's a pity that Sentient Species usually use the Sentience
to make sure that Sentience does not increase too much :-/
Yeah.
Charlie
_______________________________________________
http://www.mccmedia.com/mailman/listinfo/brin-l
