Alien Species with 2 Independent Pairs of Sexes

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Alien Species with 2 Independent Pairs of Sexes

Postby arbiteroftruth » Mon Aug 14, 2017 6:23 am UTC

Consider the following premise for the sexual biology of an alien species.

Each typical member of the species has two sets of sexual organs, let's call them type A and type B. Either type of organ is capable of reproducing with the opposite sex of the same type, but is reproductively incompatible with the other type. This species has effectively 4 sexes. A specimen can be a type A male or female, and independent of that, the same specimen is also a type B male or female. So a typical specimen can be MM, MF, FF, or FM.

With rare exceptions, the sex of any offspring is very deterministic. When a couple mates with their type A organs, the sexes of the offspring are determined by the type B genes: the child's A-sex is determined by the father's B-sex, and the child's B-sex is determined by the mother's B-sex. Likewise, when a couple mates with their type B organs, the sexes of the offspring are determined by the type A genes. The child's A-sex is determined by the mother's A-sex, and the child's B-sex is determined by the father's A-sex. In this context, the terms 'mother' and 'father' correspond to the organs involved in the physical mating. Whichever mate used the female organ carries the child through pregnancy and is called the mother, and whichever mate used the male organ does not carry the child through pregnancy and is called the father.

So with rare exceptions, the reproductively viable mating possibilities come out like so. MM + MF can only B-mate, always producing a MM. MM + FF produces MF when they A-mate, or produces FM when they B-mate. MM + FM can only A-mate, always producing a MM. MF + FF can only A-mate, always producing a FF. MF + FM produces FM when they A-mate, or produces MF when they B-mate. Finally, FF + FM can only B-mate, always producing FF.

Each sex can reproduce with any of the other three, but can reproduce in two different ways with the doubly-opposite sex, and in only one way with each of the singly-opposite sexes. This gives a total of eight distinct viable mating combinations, and each of the four sexes is the expected result of 2 of those 8 possibilities.

However, the MF/FM pair is a viable two-sex species, if not for the occasional "error" of taking one sex or the other from the 'wrong' parent. But since such 'errors' do occur with some probability, there will be an expected equilibrium population of each of the four sexes.

If the 'monosex' MMs and FFs are rare, they will almost exclusively mate with the abundant MFs and FMs, producing more MMs and FFs. If the MMs and FFs dominate the population, they will almost exclusively mate with each other, producing more MFs and FMs. So there will be some stable equilibrium of all four sexes, avoiding the "MF and FM only" equilibrium mainly by virtue of occasional 'errors' that guarantee the continued existence of MMs and FFs, until those particular combinations develop evolutionary advantages to perpetuate themselves without reliance on such 'errors'.

I invite the forum to speculate wildly about what social dynamics might arise between the four sexes as a result of this setup. Presumably, there would have been an era of MF + FM dominance before the MMs and FFs developed advantages of their own, and since MFs and FMs have true biological equality in terms of the hardships of pregnancy and nursing, those two sexes in particular seem likely to have developed only superficial differences. How might one expect MMs and FFs to be different, considering the need to attract MF and FM mates, and the guarantee of never/always being the one to carry pregnancy to term?

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Re: Alien Species with 2 Independent Pairs of Sexes

Postby Xanthir » Mon Aug 14, 2017 7:33 pm UTC

Mating schemes distilled into an easier list:

MM+MF = B-mate for MM
MM+FM = A-mate for MM
MM+FF = A-mate for MF, B-mate for FM
MF+FM = A-mate for FM, B-mate for MF
MF+FF = A-mate for FF
FM+FF = B-mate for FF

As you note, the mix sexes are viable on their own, and have the interesting social dynamic that they can decide their child's sex.

The monos dominate mating normally - if they mate with either mix they produce more of their own; only mating with the other mono can produce a mix.

Monos have no way to recover from a crash, tho - a population that for whatever reason loses one of their mono sexes can't produce any new ones, dropping the group to three sexes (ignoring transcription errors). That ends up with some *really* interesting social dynamics, then - the remaining mono-gender always reproduces itself, while the two mix genders always reproduce each other. This can end up collapsing into an interesting take on our 2-sex binary, in different ways depending on which mono is left behind.

For example, if you only have FF monos, the FFs become the "female" sex, with the mixes being the "male" sex; the only twist is that males mating with females always produces females, while males mating with each other always produces males. (There's just two types of males, and you have to mate with the opposite type to produce another male kid; whichever one takes on carrying duties produces another of themselves, which is a nice analog with the FF situation.) Males are thus happy to mate with either sex, as long as they don't have to carry it - females are easy to mate with in this regard, as there's no need to have The Argument over who'll carry.

If you have only MM monos, then MM becomes the "male" sex and mixes the "female". Males mating with females always produces more males, females mating with each other always produces more females. The split in the female sex gives us the *opposite* situation as FF-only; whoever takes on carrying produces more of themselves, while carrying from a male produces more males. This suggests a strong split in the sexes - males and females run separate, overlapping societies, where females deal with each other, and males, free from the burden of child-bearing, can maintain a patriarchy that ensures the continuation of their gender.

Even if we have all four sexes, The Binary might develop - MM forming the "male" sex and the rest forming the "female". MMs mating with two of the female varieties produce males, mating with the third variety produces females; females can mate between themselves to always produce some variety of female. This is actually pretty stable, I think - FF will tend to dominate within the female sex but any sex with males produces mixes. This ends up looking a lot like the MM-only situation, just with more complicated gender dynamics within the female set, and males can choose to produce male or female children depending on who they mate with. This feels unstable tho - it seems to need a mating patriarchy in the same way that MM/mix does, because otherwise the "females" can just shut out the males and continue on their own, changing into the mix/FF binary instead.

Or the other way, with FF being female and the rest being male (with "optional" pregnancy if they mate between each other; only MM/MM pairings being forbidden). Here, males mating within each other always produces males, but if they want to offload the carrying burden, hey, there's females who are guaranteed to carry. The kid's sex depends on the father's sex; mono will produce more males (of one of the mix varieties), while mix males will produce female children. Here mono-male seems like the most "manly" variety - they produce mix males when mating with females, and "pure" males when mating with other males, and they never carry a child. Pair this with the separate social dynamic that females might prefer mating with mix males (because it produces more females), and you get that all-important tension between the sexes! This seems more resistant against collapse into a 3-sex binary, as the males have a reason to keep females in the equation (they're a reliable child carrier, freeing up male resources), and the social dynamics between the sexes ("manly" males seem like they'd get more societal attention and thus be sexy, while "feminine" males have sexy allure arising from selfish-gene dynamics) mean females would reasonably produce both male and female children.

...shit, my fantasy world already has complicated sexual dynamics between the intelligent species, but I think I want to add in one of the 3/1 binaries somehow, they sound really interesting. Probably the MM+MF+FM/FF one, as it has less uncomfortable implications on how society would turn out, and thus seems more stable. In other words, "if you have at least one dick, you're a male".
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Re: Alien Species with 2 Independent Pairs of Sexes

Postby Liri » Mon Aug 14, 2017 9:34 pm UTC

I had typed up a response but I lost it, which is fine cause that's a lot better.

My main thing was that one of the reproductive methods will almost certainly be more onerous or resource-intensive, or like Xanthir said, any individual will try to avoid carrying the child if they have a choice. If the B mating is a real drag, MM-MF mating will occur with less frequency than MM-FF or MM-FM. So you get some tension between wanting to mate vs. not wanting to expend resources carrying the offspring yourself.

If the B mating eventually becomes vestigial, it could still have some societal (assuming these aren't lizards or something) impact as Xanthir said, where having a vestigial B male or B female could lead to some interesting outcomes.
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Re: Alien Species with 2 Independent Pairs of Sexes

Postby arbiteroftruth » Mon Aug 14, 2017 11:16 pm UTC

A binary social split of MM as 'male' and MF/FM/FF as 'female' seems most likely to me. Reproductively, MMs make the least tempting offer of all the sexes. "None of your children will share your sex, but you're always the one that has to carry them anyway. Sound good?" With such a comparatively unappealing reproductive offer, MMs have to sweeten the deal by offering survival benefits in order to be desirable mates, or the other sexes will just shut them out.

That seems likely to push MMs toward only the positive aspects of traditional masculinity. They might develop a sort of hyper-masculine chivalry, in order to advertise themselves in a protector/provider role more so than the other sexes, but since they don't have a monopoly on fatherhood, they wouldn't get away with trying to set up patriarchal domination. If they tried, once again the other sexes would just shut them out. MMs would tend to take on a more servile variety of the protector/provider role.

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