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2014-09-11 15:57 GMT+02:00 Pete Bleackley <[log in to unmask]>:

> Any mutation that increased the proportion of hermaphrodites would
> probably incur a cost in terms of overall reproductive fitness, and so not
> survive in the population.


Thinking a little more about it, having both masculine and feminine
reproductive systems would increase the number of possible health problems.
Most evident to me is the risk of both prostate and womb cancer. This
increased risk should be balanced by the increased proportion of potential
mates.

Até mais!

Leonardo


> Also, note that even for the single-sexed individuals, potential mates
> make up 77% of the population, as opposed to 50% for species without
> hermaphrodites.
>

> Pete Bleackley
> The Fantastical Devices of Pete The Mad Scientist -
> http://fantasticaldevices.blogspot.com
>
> -----Original Message-----
> From: Alex Fink <[log in to unmask]>
> To: [log in to unmask]
> Sent: Thu, 11 Sep 2014 13:11
> Subject: Re: Alien sexology (was: Native american altlangs)
>
> On Wed, 10 Sep 2014 19:12:21 +0100, Pete Bleackley <
> [log in to unmask]> wrote:
>
> >An idea I had as a result of this discussion is a species with males,
> >females, and hermaphrodites. Genetically, males are MM, females are FF,
> >and hermaphrodites are MF.
> >
> >Single-sexed individuals can breed with either of the other two sexes. A
> >single-sexed individual breeding with a hermaphrodite may produce
> >offspring of the single-sexed parent's sex or hermaphrodites. Two
> >single-sexed parents will always produce hermaphrodite offspring.
> >Hermaphrodites can breed with each other - two hermaphrodite parents can
> >produce offspring of any sex.
> >
> >The population would balance at 23% male, 54% hermaphrodite, 23% female.
>
> Would it?
>
> I assume that's some sort of largest eigenvector of some Markov process.
> But they say (not in a good place to look up a better citation now, sorry)
> that the reason mammalian births are half male and half female is because
> that's the game-theoretic optimum -- at least assuming the cost of bearing
> and raising a male and a female is equal.  Indeed, if the distribution were
> otherwise, say more than half of births were male, then a mutation which
> brought about more female births would be advantageous, as your children
> would be more likely to have a larger pool of potential mates and thus
> spread their genes broaderly; then in the long term this mutation would be
> selected for and tip the balance back towards parity.
>
> In the case of your species, hermaphrodites can mate with anyone, while
> males and females have restricted options.  So a mutation which caused more
> hermaphrodite births would give an advantage and in the long term drive out
> its competitors; and we'd expect the steady state to be where *all* births
> were hermaphrodite, unless hermaphrodites were notably more costly to bear
> or raise than the unmixed sexes.  So if you're right even in general terms
> about the distribution I'd expect such a disparity of costs, however it
> might come about.
>
> Alex
>