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Primate evolution has led to the loss of a heat cycle. This has allowed us to have children at any time of the year. But imagine a world where humans never gained that ability, perhaps even evolving more effective heat cycle depending on climate, temperature and environmental pressures.

Human culture is very intertwined with mating. It's difficult to conceive of a world where people could only become pregnant at certain times a year. I imagine that a civilized society would still have sex during other times of the year but we would not be able to conceive.

But I'm wondering more about the larger impacts in a society without the ability to breed for most of the year. What new businesses would appear? Why would they be successful. Assume that this kind of reproduction rate is sufficient for most environments on earth, allowing humans to maintain a stable number.

What would the major, most notable, differences in a world where humans have a heat cycle?

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    $\begingroup$ It's difficult to conceive of a world where people could only become pregnant at certain times a year. Women can only become pregnant at certain times a month, though. $\endgroup$ – Nolonar Oct 23 '15 at 21:53
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    $\begingroup$ Do you mean an estrous cycle? $\endgroup$ – HDE 226868 Oct 23 '15 at 21:57
  • $\begingroup$ yes that is what I mean $\endgroup$ – TrEs-2b Oct 23 '15 at 22:05
  • $\begingroup$ Anthropologists have argued that the lack of an estrus cycle is actually critical to the way human society developed. A pop-science version of this is presented in the book "Sex at Dawn", but don't take it as gospel. Certainly herd animals with seasons tend to have males that meet only for violent fights, which kind of prevents the complex cooperation that makes us human. $\endgroup$ – pjc50 Sep 9 '16 at 9:14
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Stable fertility rate

Assume that this kind of reproduction rate is sufficient for most environments on earth, allowing humans to maintain a stable number.

That doesn't work. The reason why our population grows is that the death rate drops before the birth rate does. If you reduce the natural birth rate to match the modern death rate, then we'd have died out back when our death rate was higher. Perhaps during the Black Death or after one of the larger wars.

Our old birth rate was a reasonable match for our natural death rate. What it looks like is that our ability to change from our natural death rate to our modern death rate happens before we switch from our natural birth rate to our modern birth rate. In both cases, the switch comes from interfering with natural processes.

You can't get a stable population by reducing the natural birth rate. There are reasons why it needs to be as high as it is now. To get a stable population, you need a feedback mechanism. Historically this has been starvation. If there are too many humans, enough starve to death to bring things back into balance. And of course the fertility rate drops when women are starved. Our current ability to create food has far outstripped our ability to handle waste. Perhaps you want a waste-based feedback rate--if what is important is a stable population now.

If you were willing to accept a more mystical solution, you could make reproduction require three parts: a mother, a father, and an extra piece. The most mystical version would be something like a soul. Until someone dies, there isn't a soul available to quicken a fetus. Fertility doesn't happen.

You could also make more physical versions, perhaps a gem-like apparatus that appears in a person's forehead. The mother might have to swallow a gem from a corpse to provide a framework for her ovum. The population size would be limited by the number of gems.

Estrous vs. menstrual cycles

I imagine that a civilized society would still have sex during other times of the year but we would not be able to conceive.

This is inconsistent with an estrous cycle, which is normally what being "in heat" means. In an estrous cycle, sexual desire is limited to times of fertility. What you are describing is just a menstrual cycle with a different cycle. Instead of a monthly cycle, you're suggesting more of an annual cycle.

This is much more like the current situation than anything we'd describe as "in-heat". If you want this, then you should stop using the term "in-heat". If you want to use the term "in-heat", you should understand what it means. And what it means is no sex outside of heat, whether natural or artificially induced.

Consequences

Birth control

If women could only get pregnant at one time of year, then birth control would be unnecessary for most of the year. Just don't have sex in June or whenever.

Fooling the cycle

How does the cycle know that it's time? Day/night cycle? Temperature? What? Whatever it may be, they'd explore ways to change the cycle. Much of the effort that we put into birth control might find its way into birth promotion instead.

In-heat

I actually think that it would be more interesting to have a true in-heat scenario. People would only have sex when the female was in-heat. To have intercourse outside the normal cycle, the female would need to be artificially stimulated. Males would respond to the female arousal.

In-heat females would take time off from work and seclude themselves until normal pheromones resumed. Romantic getaways would involve really getting away. Only out-of-heat females would be able to make contact with the couple.

The concept of rape would change. They'd really blame the female, since it would be the female desire that drove sexual encounters. Perhaps they'd have laws against in-heat females exposing males to their pheromones during their in-heat period.

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  • $\begingroup$ "You can't get a stable population by reducing the natural birth rate. There are reasons why it needs to be as high as it is now. " What is this? What would happen if we had some way right now to cut the natural birth rate to match the current death rate? $\endgroup$ – The_Sympathizer Jan 30 '16 at 9:54
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    $\begingroup$ @mike3 If 100 people were born as 100 people died, not all of them would make it to reproduction age, so you would get a declining population as people died of accidents, etc. $\endgroup$ – Azor Ahai Jun 24 '16 at 3:47
  • $\begingroup$ So what happens if you reduced the birth rate to "just the amount above the death rate it has to be in order to match that barrier"? $\endgroup$ – The_Sympathizer Jun 25 '16 at 6:11
  • $\begingroup$ @mike3 That would be fine for that moment, but it would leave things off when the death rate changed. That's why you need a feedback mechanism that adjusts the birth rate to match the current death rate. If you set the birth rate in stone age times to match the modern death rate, humans would have died out in stone age times when the death rate was higher. Note that the current birth rate is artificially low due to the widespread use of contraceptives. In fact, the middle class in modern Japan, Europe, and the US have an average birth rate that is slightly below replacement level. $\endgroup$ – Brythan Jun 25 '16 at 18:12
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Honestly I don't think you would see a huge change.

Assuming males were only interested in "in heat" females then pornography and related industries would be far less profitable. Additionally you may well see a big change in advertising as "sex sells" may also not be the case, or at least only used in targeted advertising to those in a suitable state.

You may see some businesses appear around the artificial pheromone business if it's pheromone driven. Either way no doubt people will come up with ways to stimulate people to go in-heat (whether they actually work or are just a placebo) or to control and reduce it going into heat.

But for the most part people would still need everything that we need, would want most of the things we want, so all the businesses and services around everything except sex would carry on unchanged.

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