I stumbled across the tropes page from "A Brother's Price" the other day. Basically, the novel takes place on an alternate Earth in a country called Queensland, where only around one in every ten births is male, all the rest being female. What could cause such an imbalance in the human male/female birth rate?
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3$\begingroup$ Ask on scifi.stackexchange.com if the book ever says why. $\endgroup$– wetcircuitJan 31, 2018 at 21:44
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3$\begingroup$ See the planet Grayson in David Weber's Honor Harrington series. In mammals, the default body plan is female; switching the development of the embryo so that it develops into a boy and then into a functional male adult is a complicated process. When the colonists first arrived, they had to do some emergency genetic engineering under time pressure and with limited resources. Mistakes were made. $\endgroup$– AlexPJan 31, 2018 at 21:44
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$\begingroup$ A lot of hive insects have this tendency. $\endgroup$– A. C. A. C.Jan 31, 2018 at 22:03
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$\begingroup$ the Y chromosome is a delicate thing... $\endgroup$– Erin ThursbyJan 31, 2018 at 23:28
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4$\begingroup$ You have got to stop asking duplicates of your own questions. $\endgroup$– kingledionFeb 1, 2018 at 1:08
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4 Answers
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It can be antibodies in the mother's vagina that target Y-carrying sperm. This is easy to comprehend and there are anecdotal stories of this sort of thing.
It can be down to something similar to Rh factor, if blood types and gender are genetically linked. This is not known to occur, but a little genetic shuffling in a fictional world can make it a realistic outcome. You'd also need to play with family size; Rh effects impact later-born children more than first children.
It can be down to a fictional physiological response in men: Consider, as population declines, men start producing far more X sperm ... because we need more women than men to get the population load back up.
It can be down to when intercourse occurs during the menstrual cycle (X sperm out-survive Y sperm in the woman's reproductive tract, so intercourse days before ovulation is more likely to result in a female baby.)
Here is a science article that looks at gender selection of offspring in mammals.
It can be many other things; these are for starters.
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$\begingroup$ Please copy your answer over to the question this is a duplicate of. $\endgroup$ Feb 1, 2018 at 4:01
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Perhaps a fatal mutation on the Y chromosome affects the child's development such that only 1 in 10 make it to birth. Or perhaps a disease evolves that targets a trait that only exists on the Y chromosome so that the disease only affects males.
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$\begingroup$ This has the beginnings of a good answer but needs to be fleshed out more. Maybe explain how that would cause the imbalance and go into more detail as to why it would be a good method. $\endgroup$ Jan 31, 2018 at 22:44
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You have two choices
Evolutionary, natural selection favored women who birth females, perhaps a matriarchal society where females are highly valued and a women with that rep has a lot of husbands. Or some other reason leading to the same result.
Environmental, take your pick, temperature, light levels, air pollution, purposely taken drugs... it's a story.
You could merge the two, there is a drug available that will 90% of the time ensure a pregnancy is female. Female offspring are highly prized in society and provide a women with status and power. So women take this drug.
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$\begingroup$ Wait, that's backwards... If evolutionary natural selection favors women by numbers, you could either end up with a super patriarchal society where the men have many wives, a matriarchal society where the men are a shared resource of the community - but still probably have status. The more common women (or men) are the lower their relative status, and the opposite is true. The matriarchal case where the top women are able to hoard access to the few men is definitely interesting, but seems unstable. Like it would lead to violence. Great for plot, but not sustainable as an evolutionary pressure $\endgroup$– MParmFeb 1, 2018 at 5:23
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$\begingroup$ @MParm all societies lead to violence eventually, but glad you understand the fine details of evolution so well $\endgroup$– KilisiFeb 1, 2018 at 6:19
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$\begingroup$ me too ; ) In all seriousness, I will nit pick at the idea that any society where one sex is common and one is uncommon that the uncommon sex has a low status. Now the nature of that high status might not be nice (a lot of the patriarchy is based on the fact that women have historically been a critically valuable resource for the continuation of any civilization). I guess your idea of concentrating all the males in a harem with access to very few females, and 99% of the population being unable to breed just strikes me as counter intuitive and I can't figure out where you're coming from. $\endgroup$– MParmFeb 1, 2018 at 21:20
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Temperature, because they are a reptile species with temperature-dependent sex determination.
The eggs that are too warm or too cold become males. Eggs in the goldilocks zone become female.
Because the species no longer lays eggs in the ground, inconsistent incubation temperature is no longer an issue and so most children are female.
answered Jan 31, 2018 at 21:57
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$\begingroup$ I will specify that the Earth is still populated by HUMANS. $\endgroup$– Preg-FanJan 31, 2018 at 22:17
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1$\begingroup$ You said "Alternate Earth", not "Earth". $\endgroup$ Jan 31, 2018 at 22:21
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1$\begingroup$ I meant like an alternate history type of thing, not a scenario where humans never evolved at all. $\endgroup$– Preg-FanJan 31, 2018 at 22:23
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$\begingroup$ Please copy your answer over to the question this is a duplicate of. $\endgroup$ Feb 1, 2018 at 4:02