On 13/07/2006, at 3:23 PM, Alberto Monteiro 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 - even in the situation
you're alluding to, it's still an advantage to females to produce
sons as well as daughters - 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.
I am still waiting for the Hardy-Weinberg equilibrium models!
http://en.wikipedia.org/wiki/Hardy_weinberg
Wikipedia, the Borg of all Knowledge :-)
It's not bad in some areas, certainly. Can be a great gateway to some
real sources.
More likely, IMO, are Baxter's "coalescents",
populations of eusocial humans, but even they'd require some
special conditions to evolve.
I am not aware of those groups.
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
There's one mammal group that has eusociality - the mole rat. 2
species, of which the weirdest is the naked mole rat (it's even
poikilothermic, which is very unusual for a mammal...). Baxter
postulates a human group that becomes eusocial and undergoes rapid
evolution in his novel Coalescent. But even mole rats are only
slightly skewed, and actually biased towards males (1.4:1, or 58%
male) where you'd think that eusociality would cause female bias.
Males evolved *because* they were required to cause genetic
variation.
Or, more correctly, sex may have evolved to promote genetic
variation. Sexual dimorphism came later. It's not as cut and dried
as you seem to think, it's still one of the great issues in biology.
I know it's not so simple. Before males appeared as a separate
subspecies, all creatures were hermaphrodites.
Or asexual.
Maybe there's a genetic advantage for the species, or to form
new species, in having two sexes over hermaphroditism.
Advantages to the individual.
Mutations are genetic changes at points in the genotype, not
phenotypic changes to population. Assuming you actually mean
"evolve" not "mutate", then, well, it's inevitable. Even the
changes you're talking about are evolution.
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.
Charlie.
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