So, this problem is kind of a two-in-one; arguably two different issues but very closely related, so I'm posting them as one question.

I'm designing a lineup of fantasy races for a roleplaying setting, and I think I want to have two single-gender player races. My favorite idea for how is to have Half-Giants for the masculine and Witches for the feminine, but I'm not certain how this works genetically.

EDIT for clarity: More specifically the so-called Giant race has male and female members, with the men being significantly larger than the vast majority of Humans - 8' tall on average, more broadly built, thick-boned and muscular. Giantesses on the other hand are just noticeably larger (6' on average and more robust) than the average Human man. Half Giants, who are intermediary in size, exist only in male form; there are no female Half Giants either as a playable option or in lore.

The Witch race (men and women) mostly resemble normal humans, but the women are more naturally attuned to magic. The men (Warlocks) lack this magical affinity and so are ostensibly identical to Mundane Human men, except in the fact that they can produce Witch daughters. So a player might play as a Warlock for lore reasons, but they have the same stats as Human players.

Since both the races of Giants and Humans are comprised of both males and females, that implies that in the case of Human-Giant mating, female zygotes are formed as often as male, but only the males come to term. I can't remember where I heard this, but supposedly all first-generation sapiens-neanderthal hybrids were female because of some minor genetic incompatibility, and that would seem to imply that the Y chromosome is the cause of the incompatibility; but could the inverse be the case, where the Y chromosome causes compatibility where otherwise hybridization is not feasible? I'm not aware of any real-world precedent for that.

Witches on the other hand are always female, and best I can figure for how this works is that one needs two X chromosomes with the witch gene in order to be a "full-blooded" Witch; females with only one are "Half-Witches" who are functionally identical to Mundane Humans, as are male "Warlocks" who are required to produce more full-blooded Witches. I like the logic of this as it applies to potential plotlines, but I don't think the two-X requirement works that way. From what I understand, only one of the X chromosomes in biological females is active, with the other being dormant; and if all it takes to go full Witch is one Witch gene, that means all Warlocks have the same functional witchy traits as the other Witches, which means Witches would have to be a standard two-gender player race, and I would prefer just one.

Easy solutions I don't prefer:

  • Female Half-Giants and male Witches; this is a lot easier to explain, with the Human and Giant genomes being incompatible at the Y chromosome and the Witch genome being entirely on the Y, but it lacks aesthetic appeal for me and I suspect most potential players on several levels. It has its ups too, but not enough compared to the other way.
  • Asexual Witches; this is boring. I like the premise of arcane creatures whose bloodline is interwoven with humanity rather than completely separate; there's a lot more story potential there.
  • Female Half-Giants do exist but might as well be full-blooded Humans, like Warlocks; I considered this, but I much prefer the premise of Half-Giants being sort of uncanny mulish men produced by two species barely chemically compatible, always male and always sterile, giving Half-Giants more potential conflict and reminding the audience that Giants really are a different type of creature rather than just big dumb cavemen.
  • Y chromosome somehow suppresses Witch traits, the same way male hormones suppress the growth of breasts, uterus etc.; this is a clean explanation, but it removes a potential story element of the Lost Bloodline, where characters don't know that they have Witch blood; if there are no dormant female Witches but rather all females with the potential to pass on the Witch gene are proper Witches themselves, it's extremely implausible that any family would not know that they are Witches. If this is the only way all-female Witches makes sense, I'll settle for it, but I'd prefer to have the potential for dormant females.

So, in brief: Is it plausible to have two species to whom hybrids are always or at least overwhelmingly male, and a distinct genetic trait that is only expressed in females who have the trait on both X chromosomes?

  • 1
    $\begingroup$ What makes a warlock different from a witch? Since so far to me they just sound like the male/female sides of a spell casting humanoid, unless you mean that despite being 'full-blooded' they can't actually do anything magic-wise. $\endgroup$
    – Lemming
    Commented Dec 11, 2021 at 13:02
  • $\begingroup$ After some thought I realize now you may have meant warlocks are simply males with a witch parent or X gene, same as a half-witch who is functionally equivalent to a mundane human, but suffice to say if I were a player of your game I'd be rather confused initially that despite being called warlocks they might not be able to do any magic, if that is your intention for them. $\endgroup$
    – Lemming
    Commented Dec 11, 2021 at 13:07
  • $\begingroup$ @Lemming The gameplay mechanic of playing a Witch is that she is potentially better at magic but also more vulnerable to hostile magic. I want normal Humans by contrast to be resistant to magic, though not unable to use it, as opposed to the usual "Humans are average" generic stuff in most fantasy RPGs. Warlocks, not expressing the iconic Witch traits, would be resistant to magic like the Mundane, instead of more receptive to it. There may also be Witch-specific cosmetic options like purple eyes or green skin, not seen in normal Humans and Warlocks. Does that clear it up? $\endgroup$ Commented Dec 11, 2021 at 13:09
  • $\begingroup$ And yes, genetically a Warlock is a male, XY, wherein the X contains Witch genes as opposed to Mundane genes. $\endgroup$ Commented Dec 11, 2021 at 13:11
  • $\begingroup$ That makes things easier, yes. Would you be satisfied with a tigon/liger situation with a female half-giant? I'm thinking that female half-giants might experience dwarfism, being smaller instead of being larger than humans, at least, I'd think half-giants are at least a bit larger than regular humans(I don't recall heights and such being given, just an assumption) $\endgroup$
    – Lemming
    Commented Dec 11, 2021 at 13:47

2 Answers 2


These aren't hard to handle.

The Half-Giants are a straightforward case of Haldane's rule. Note that the male Half-Giants could still be the equivalent of a mule or hinny, depending on whether the Giant parent was male or female, with different characteristics. (You may need a midwife witch to get one of those possibilities to work out in the end)

The Witches and Warlocks are similar to a garden variety sex-linked recessive trait. A normal human X chromosome, if present, represses it; otherwise not. You add the wrinkle that a normal Y chromosome also represses it. That is plausible if, say, the trait is located in the pseudoautosomal region (PAR) of the Y chromosome, which is a piece of the Y that is similar to the X and recombines with it. But since you don't have any male Witches, the recombination can't be allowed - but there are low recombination regions within the PAR where that is plausible. However, this approach doesn't rule out the existence of some other population with active Warlocks with an active witch gene on the Y chromosome after some rare recombination event.

You correctly recall that there is such a thing as X-inactivation - but that happens at a mosaic level throughout the woman, so both X chromosomes still have genetic effects. Presumably if you have microscopic patches of Witch and Whatever tissues throughout your body, they don't all pull together as a team when it comes time to turn somebody into a frog.

One idea that might prevent active Warlocks in any population encountered is if the witch gene is only expressed from an inactivated chromosome, like Xist, and it is still repressed in normal people by some companion transcript (whatever) that is active on non-inactivated X and Y. You have to suppose the X-inactivation dependence of witch is somehow integral to its function in a way that won't change with a simple mutation; whereas loss of the repressing transcript whatever is simply a new mutation matching those of your existing witches. That is a bit elaborate, but by no means the strangest genetics you can encounter.

  • $\begingroup$ Firstly, yes there are full-blooded Giants. They are a separate species which will almost certainly not be playable because 1, they're too big and strong to be balanced to the point where you would have to make a whole game built around just playing a giant, and 2, their different psychology/intelligence would make accurate RP more difficult and less likely. Half-Giants are the result of a Man and Giantess or Woman and Giant mating. I thought that was implicit in my OP. Also I did say that Half-Giants are sterile, like mules. That adds some potential drama and conflict. $\endgroup$ Commented Dec 11, 2021 at 13:55
  • $\begingroup$ Also, I like the bit about genetic mosaics. I'll need to re-read and do a bit of research to understand some of this answer, but this might be what I'm looking for in regards to Witches. $\endgroup$ Commented Dec 11, 2021 at 13:56
  • $\begingroup$ Oh phooey. I fouled that whole section up because I read "Human-Giant" as "Half-Giant" without thinking. $\endgroup$ Commented Dec 12, 2021 at 13:19

Giants are Protogynous

The giants in your setting could be protogynous, where they are born female, and only turn male later in life. This explains why female giants are smaller, and can also give reason for your idea

These giant's gender shift could be caused by a subtle hormonal change. However in half-giants, some genetic issue causes an overproduction of these hormones, which means that they always turn male right at puberty


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