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Alex Fink, On 11/09/2014 13:11:
> 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.

Must the assumption be not only that the cost of bearing and raising a male and a female are equal but also that, independent of the numbers of each sex, males and females have an equal chance of attracting a mate? If not, then one can quite easily imagine a scenario in which the game-theoretic optimum is far from 50--50: for example, if one male can impregnate many females, and is happy to do so, then from the point at which there are enough males to impregnate all females, one is better off having female offspring, since females need not compete with one another as much as males, it being easier for a female to get impregnated than for a male to be an impregnator; the female--male ratio could, say, be 9--1, and with a harem-based bonding structure. (Or has my reasoning been betrayed by wishful thinking?)

I do like Pete's idea, I must say. For 54% of the population the pool of potential [reproductive] mates is 100% of the population and for the other 46% the pool of potential mates is 77% of the population, so on average the pool of one's potential mates is 89.5% of the population. Much better than the 50% that humans must endure. I wonder how heterosexuality would work in Peteworld: if hermaphrodites had mixed sexual traits then the heterosexual (MM, FF) would have to be attracted to the sexual ingredient they lack -- Fness/Mness -- but not repelled by the ingredient they have (for if repelled by hermaphrodites, the pool of potential mates would shrink by two thirds). If people in Peteworld aren't repelled by the sexual ingredient they have, and sexual congress is partly hedonic, then everybody would be at least Kinsey 1--5 (or 2--4, but certainly without the extremes of 0--6), which would mean that for everybody the pool of potential hedonic sexual partners would, paradisiacally, b
e about 100% of the population.

--And.