I'm at the very early world building for a potential story where I have a sort of humanoid feline species that I need to have been known as expansionist and/or war-like in the past but not be aggressive in the world's present.

I'm toying with the idea that the species has regular heat cycles, which were strong enough to make it hard for a female to resist reproducing. Once society and technology developed enough that infant mortality had dropped the inability to resist reproducing started to lead to difficulty with over population. Thus the species ended up being involved in a number of expansionist campaigns trying to grab up enough territory to support their rapidly growing population, and of course the war's themselves helped to 'thin out' the excess population by removing a decent number of the young males. The species eventually discovered a way to produce a heat suppressant that is now commonly used to prevent heat, so the 'modern day' species no longer struggles from excess population and without that issue no longer needs to expand.

I'm trying to determine what the introduction of such strong heat cycles may do to the species as a whole, both in the past and in modern culture influenced by the past struggle with heat cycles. How would a culture adapt to the recognized issue that excess reproduction caused by regular heat cycles would often strain the nations ability to support it's population? Obviously I intend for expansionist conflicts to be one result, but what other impacts would there be? During times of peace, between wars, what would the species do, both on an individual level and on a governmental level, to deal with the risk of over population? Are there any implication to how this would affect more modern culture of the species?

The time during which over population was an issue would have a roughly Tolkien Lord of the rings feel, both in terms of technology and how the various species interacted with each other. Magic does exist in this world, but is relatively limited and is unlikely to provide a solution for over population.

  • $\begingroup$ What's "'Tolken' era"? Did you mean Tolkien? And if so, do you mean "like in LotR", or like Earth at the time Tolkien was writing? $\endgroup$ – Matthew Jun 3 '20 at 18:29
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    $\begingroup$ Birth control has a very very long history. It seems like contraception would become a major focus of this population. en.wikipedia.org/wiki/History_of_birth_control $\endgroup$ – Andrew Brēza Jun 3 '20 at 18:45
  • $\begingroup$ @Matthew corrected that, but yes I meant LoTR $\endgroup$ – dsollen Jun 3 '20 at 18:51

Your species would likely have an easier time dealing with overpopulation issues than humanity

Humans are unusual among animals in that they have a combination of two physiological traits which by themselves already are uncommon among animals.

  • Concealed ovulation: Human females do not produce any visible signals of high fertility or ovulation. In most animals, females produce very visible signs that they are close to ovulating to advertise to males that they are the best choice of mate because they are most likely to bear offspring. In extreme cases you have things such as the sexual swellings of baboons and many primates, but the ovulation of most species can be easily detected by things such as the scent of certain hormones in the urine. Humans don't, and this has been suggested to be a feature, not a bug, because it encourages males to stay around females and assist in the care of offspring (which increases survivorship in such a K-selected species as humans). For all the studies of humans suggesting that exposure to pheromones put out during ovulation might subconsciously affect human behavior, there is no evidence that humans can consciously detect if another human is ovulating and modify their behavior accordingly.
  • Lack of a constrained mating season: Unlike most animals, humans do not have a strict timetable for breeding. Humans may be more likely to breed at certain periods of time, but our species has sex throughout the year as can be evidenced by the fact that birthdays span all 12 months. So it is not like other species where desire to mate peaks in a set period during the year and then dwindles to nothing later.

The combination of these two features makes human reproduction in general a Russian roulette among animals. Whenever humans mate, we have no way of knowing whether it will result in pregnancy or not because there is no set season when humans are fertile and there is no way of knowing whether the female is at peak fertility. Women often track their ovulation cycles to avoid peak fertility, but the fact they have to chart it and can't just tell they are fertile demonstrates how hard it is to keep track of these things.

This is how you get things like teen pregnancies, unplanned babies, and a huge market for contraceptives in humans. Our breeding system is extremely chaotic and hard to control or plan for. If human beings had a visible estrus cycle or a set breeding season population control would be exceedingly simple, just don't have sex during the extremely forecasted breeding season. Even if the females had a hard time controlling a desire to mate during the breeding season, males would be able to easily determine whether or not they wanted offspring by taking one look at the female and going "this female is in heat. I do not want/cannot support a child right now, so I'll just wait the few weeks until she is out of heat and there is no risk of producing a child". If human reproduction were as predictable as your species we wouldn't be in an overpopulation crisis right now.

If you want there to be an overpopulation crisis but keep the distinct heat season, the best way to do it is to have severe negative side effect for not reproducing during the breeding season. This exists in nature. Female ferrets will get very sick if they do not mate during the breeding season, and this cannot be cured except by having sex. The rump of baboons swells during estrous, and there is evidence that in addition to individual genetics the degree of swelling is correlated to how long they have gone without mating. If they don't mate the swellings get worse and worse until they negatively affect the health of the female.

Of course, the question then becomes why doesn't the species, if they are sapient, just invent methods of contraception early given how big of an issue controlling reproduction is for their society. To go back to the ferret example, it is the act of mating that resolves the sickness, so male ferrets with vasectomies work just fine. Things like this (or less extreme forms of barrier or hormonal contraceptives) would probably work in other species with similar mating habits. This is the kind of species that would invent the morning-after pill before the printing press.

  • $\begingroup$ You're assuming that the males are able to control their urges. One could argue whether this is true for humans. For a species with a definite estrus cycle, it's not implausible that males in the presence of a female "in heat" would be akin to watching porn while thoroughly inebriated. The OP didn't specify if this is the case, but you're attempting a Frame Challenge that is plausible but not inevitable. OTOH, it's not that hard to create devices that will prevent copulation, especially if the parties using them are doing so willingly (when sober). $\endgroup$ – Matthew Jun 4 '20 at 13:58

Humans also struggle with a hard-to-control urge to reproduce.


And not just sometimes. Having children is a biological imperative and also makes economic sense in many situations. Entire disciplines could be dedicated to the topic. My summary:

  1. Decrease infant mortality. You do not need to get pregnant over and over to have 1 child who will support you in your old age.

  2. Long term economic viability of the family less dependent on numbers. If your subsistence farm (or whatever cat people have) works just as well with 5 family members as with 25, you will go with 5 all other things being equal. Improved food production tech can help with this.

  3. Social safety net. You do not need loads of kids to support you in your old age because the state will help.

  4. Put reproduction under intelligent control. Females choose when they get pregnant, both as regards biology and reproductive hormones as well as sociology and the right to choose when they copulate.

  5. Educate the citizenry about how pregnancy occurs, and various ways it can be avoided. Still a controversial subject in the US.

  6. Additional measure: the state could disincentivize excess offspring. The Chinese are the model for this with their one child per couple policy. There are other ways this could go too.


a state backed contraceptive campaign should do nicely. or have contraceptives be mandatory by law once an individual of this species reaches a certain age.

the solutions to this problem are very simple.


If chemical or barrier contraceptives are not readily available...

Infanticide, and/or abortion. It's not nice, but infanticide does solve the problem, and has been practiced by humans.


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