Ejaculation is the discharge of semen from the male reproductory tract, usually accompanied by orgasm. It is the final stage and natural objective of male sexual stimulation, and an essential component of natural conception. Despite this, "dry" orgasms do occasionally happen. This occurs when the final stage is reached with no actual discharge due to the testes having run out of juice.

This species of humanoid is similar to baseline homo sapiens, with a few key differences. I would like to design a mechanism for voluntary control over the discharge of semen, like an on or off switch that can be activated at will. This would be meant to be a natural and foolproof form of birth control and eliminate the occurrence of unwanted conceptions.

How can I make this possible?

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    $\begingroup$ fullproof Any number of medical conditions would likely make your mechanism fail. There would still be a need for contraception. Also note that sex (if done correctly) is distracting, and relying on a conscious thought to activate or deactivate the production or non-production of semen would be hopelessly prone to error. $\endgroup$ – StephenG Nov 18 '18 at 13:04
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    $\begingroup$ Human sexuality is fundamental to the perpetuation and survival of the species. From a remarkably sociopathic point of view, who would want the hassle of raising children if the drive to create them were not to great and (*cough*) entertaining? Though you'll get answers without this request for clarification, what is the evolutionary drive for perpetuation in your species, since that appears at this point to be replaced with the word, "meh"? $\endgroup$ – JBH Nov 18 '18 at 15:17
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    $\begingroup$ @StephenG, I'm not an evolutionary biologist, but I wouldn't be surprised if one explained that our perception of entertainment is a natural consequence of the evolutionary drive toward reproduction. In other words, we interpret the action as entertaining when in reality we're driven (forced, wired) to it in the same way we find food enjoyable because we're driven to eat. After all, what is pleasure but a reaction to doing what we're wired to do and pain a reaction to doing things we're wired not to do? (And if that answer isn't a 250-page PhD dissertation, I don't know what is.) $\endgroup$ – JBH Nov 18 '18 at 16:24
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    $\begingroup$ Evolution is going to undermine any attempt, any malewho accidentally inseminates a female is going to have a distinct evolutionary advantage. $\endgroup$ – John Nov 18 '18 at 20:18
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    $\begingroup$ If you are just concerned with population control has you considered having an real estrus period unlike the 24/7 system human use. This is one of the things keeping chimp populations low. Its an easily lost adaptation however. $\endgroup$ – John Nov 18 '18 at 23:44

10 Answers 10


You can you go two ways, I think.

Way 1:

Sperm production follow a periodic cycle, roughly like egg production in the female does. This means that only intercourse during the right moment will be fertile, any other time will be non fertile. To prevent extinction of course you need a synchronization of female and male periods.

Way 2:

The male has to consciously decide for emitting semen, something along the line of the western interpretation of tantric sex. A muscular contraction at the right moment can simply stop the seminal emission.



Not having sex is a "voluntary control over the discharge of semen." It is also a "natural and foolproof form of birth control and eliminate[s] the occurrence of unwanted conceptions." If you don't have sex, you won't have kids.

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    $\begingroup$ This answers the letter of the question, but not the spirit. It should be a comment, not an Answer. $\endgroup$ – Beta Nov 18 '18 at 15:20
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    $\begingroup$ @Beta, I disagree. Frame challenges are a time-honored tradition on this site, and Kingledion is a master at answering the letter of the question while challenging its spirit. I could wish that all answers were this elegant. $\endgroup$ – JBH Nov 18 '18 at 16:28
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    $\begingroup$ @Beta I think this answer points out that the mechanism requested by the OP is highly redundant. From a science-based basis, there is no need to develop a biologically expensive mechanism to reproduce (pun!) something that is already a feature of all creatures that reproduce sexually. $\endgroup$ – kingledion Nov 18 '18 at 17:19
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    $\begingroup$ Of course you can't be using humans, or even likely primates, abstinence fails horribly in humans because the human brain is built to as incompatible with abstinence as possible. $\endgroup$ – John Nov 18 '18 at 23:42
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    $\begingroup$ @Rekesoft The point is, the smallest baseline change is to make abstinence more effective, not to introduce some other biologically expensive mechanism. But, effective abstinence would not make much sense evolutionarily, neither would a mechanism in the testes to prevent ejaculation. $\endgroup$ – kingledion Nov 19 '18 at 15:11

Retrograde ejaculation

Retrograde ejaculation occurs when semen which would, in most cases, be ejaculated via the urethra is redirected to the urinary bladder. Normally, the sphincter of the bladder contracts before ejaculation forcing the semen to exit via the urethra, the path of least resistance. When the bladder sphincter does not function properly, retrograde ejaculation may occur. It can also be induced deliberately by a male as a primitive form of male birth control (known as coitus saxonicus) or as part of certain alternative medicine practices.

You want some deal where the men can fulfill their culturo-evolutionary imperative to have lots of sex, but shortcircuit the fitness benefit that it historically provided. That will work until mutant men who can't do the short-circuit overwhelm the population with their progeny.

But in the short term, your men can be yogi masters (if that was not already the case) with conscious control over the bladder sphincter. Sex occurs normally, with the ejaculate captured in the bladder to be voided against a tree at some later time. Out of distaste for banality, I hope you make these men and their partners be capable of all sorts of other yoga sex tricks too.

  • $\begingroup$ Exactly how was this consciously achieved $\endgroup$ – anon Nov 19 '18 at 19:32

These are humanoids so we don't have to modify human men.

In their society males, like seahorses raise young.

Male seahorse giving birth https://youtu.be/MsHCqrrU-Gk

This is very energy expensive so males don't want to be having offspring all the time.

However females will wander if they don't get regular sex. Therefore, through evolution, the males have a mechanism for ejaculating only when their previous brood is self-sufficient.

  • $\begingroup$ +1: This is the answer I came to add. Make the young depend on the father for a long stretch of time (e.g. have the father breast feed, or have it that neither mother or father can feed the child alone). natural selection will do the rest, and build in a mechanism that ensures the parents aren't over burdened with children. $\endgroup$ – Binary Worrier Nov 19 '18 at 17:52

Intelligence has allowed mankind to thrive, and your humanoids might have evolved it out of a necessity.

First option: disease. We already have a common disease that has a ludicrous chance to kill an unborn child. Biology found a solution: kissing. By kissing you exchange saliva and if the man has the disease he'll infect the woman. By the time the disease becomes dangerous to the baby the woman has created an immune response and the baby is safe. Now imagine a disease that primarily lives in the reproductive organs and the man will have an idea when he's infected during sex. The disease works like the flu and changes each year, so you dont stay immune. If the disease survives long enough to have a high chance of killing the child the man can choose not to ejaculate but continue sex normally to both increase the chance of infecting the woman and give her time to become immune and for the social benefits of sex.

The second and more elaborate option: Imagine a world where there are large stretches of time where unborn children and babies have almost 100% chance of dying. Its a waste of time, energy and potential children as you need to recover after a failed attempt. If these stretches of time are happening at predictable intervals biology would simply adapt the cycles to those intervals. If they arent predictable only two solutions remain: Make sure your biology can create children at a rapid pace or become intelligent enough to learn all the signs when children wont be viable. For potenial comments like "biology would learn the signs of the event and not need intelligence" there would need to be several events that seperately may not cause death in the babies but combined would cause that death.

Sex would still be used as a social interaction between the man and woman in those times children shouldnt be born, but to ensure no babies are born the man would prevent ejaculation.

  • $\begingroup$ In the second scenario, there would be more selection pressure on females than males. So the females would adapt to be infertile during the dangerous seasons (with or without conscious volition), and the selection pressure on the males would vanish. $\endgroup$ – Beta Nov 18 '18 at 18:36
  • $\begingroup$ @Beta that would be assuming that these are actual seasons rather than events of different time length and unpredictable starting periods. Otherwise you would be absolutely right. Even so evolution isnt "smart", and having something develop on the males is completely possible especially if some muscle cluster or similar is in the right position. This would unburden the evolutionary pressure on the females: pick a man who has more control during bad periods and you get more children during good periods, and with that the men without control die out. $\endgroup$ – Demigan Nov 18 '18 at 21:20
  • $\begingroup$ I made no such assumption. Such an adaptation will arise more quickly in females than in males... Unless you are assuming that females aren't intelligent. $\endgroup$ – Beta Nov 19 '18 at 1:41
  • $\begingroup$ @Beta Considering that ejaculation is a more timed procedure compared to ovulation which is a long cycle of hormonal maturation, transportation and evacuation of the eggs it's far easier to stop the ejaculation through a conscious effort. $\endgroup$ – Demigan Nov 19 '18 at 9:06
  • $\begingroup$ @Demigan Your comments are unclear (or at least inconsistent with your answer). Any such periods of stillbirth or whatnot would be pressure on the females - not the males, whose contribution is done prior to conception. Females would then adapt to unpredictably changing circumstances. You would be relying upon males somehow predicting the unpredictable unhealthy periods well in advance. Psychic sperm are less likely than women not ovulating (a limited resource) or miscarrying when circumstances change to being unlikely to produce viable offspring (exactly as we see in reality). $\endgroup$ – pluckedkiwi Nov 19 '18 at 16:11

We humans are capable of doing it.

Millenia ago the people in India developed some traditiond which are called Tantra. Among such traditions, there is tantric sex. Search on Google or Amazon... There are thousands of books on it written just this century.

Central to tantric sex for men is developing the ability to have dry orgasms without being dry. This is done through breathing and muscle control, akin to (or including, depending on the view) yoga practices. It is said to become second nature once you achieve it, and allows for a man to have multiple orgasms.

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    $\begingroup$ I have heard of it. But I thought it was just bullshit and a marketing tool to get people's money, such as the 1 hour extended orgasm. $\endgroup$ – Incognito Nov 18 '18 at 13:55
  • $\begingroup$ Even if there is no ejaculation, this is far from foolproof. $\endgroup$ – Sulthan Nov 18 '18 at 16:46
  • $\begingroup$ @Sulthan What dangers are there? $\endgroup$ – Orphevs Nov 18 '18 at 16:49
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    $\begingroup$ @Orphevs Living sperm can be present in precum, even if it's a rare case. It's why "pulling out" is not a safe method to avoid pregnancy. $\endgroup$ – Sulthan Nov 18 '18 at 17:03
  • $\begingroup$ @Sulthan tantric sex prevents precum as well. The risk is more in poor skill. $\endgroup$ – The Square-Cube Law Nov 18 '18 at 18:01

Proceptive (?) medication - Males have to take a drug to produce sperm/gametes or one of the other necessary components of semen.

I'm envisioning something plant- or fungus-based...

Your early hominids live in an area where this organism is plentiful--so plentiful that they never really have to think about actively producing sperm. Some males don't like the taste, so they rarely eat it and maybe never have children or have very few. Groups that splinter off and leave the home area only reproduce if they move to an area where the same plant grows or if they take the dried fruit with them. Maybe they aren't consciously aware of it, but there's definitely a connection between the fruit and reproduction. They might even have a sex/harvest festival when the fruit ripens.

Over time, as agriculture improves and your hominids explore their planet, their diet becomes more varied, the sperm fruit is less of a staple, and the birthrate slows down. It has become a cultural tradition for explorers to always carry a potted sperm plant with them. Sailors have been known to mutiny and force their captains to turn home whenever the potted plant dies. Horticulturalists attempt to create sperm fruit hybrids and succeed, introducing more variety into both the plant and the hominid species.

Perhaps the sperm fruit plant is very climate-sensitive. That could be a form of natural population control. In lean times, the plant and the population don't grow as much, so there are fewer new mouths to feed. And it could lead to developing trade between groups that live in areas where the plant will grow and the areas where it won't. This sets up a few different scenarios.

  1. A global climate catastrophe wipes out 90% of the world's population. Maybe only half of that is wiped out by the actual disaster. The rest simply live their lives and die without the ability to reproduce. Only those isolated areas where the plant can grow have thriving populations. This could lead to development of cultural variations.

  2. Politics vs. Science - Your hominids have established a clear link between the sperm fruit and reproduction. Now there's a race to create a shelf-stable synthetic version so that they're no longer dependent on the fruit. The government tries to control growth and distribution of the sperm fruit, causing groups of rebels to periodically attempt to steal the plants and/or overthrow the government.

  3. Space drama - Your scientists haven't yet succeeded in developing alternatives to the sperm fruit. Or they have, but the synthetic version has a short shelf life/is costly to produce. Space colonists must take living sperm fruit plants (either in stasis or specialized terrariums) with them on their colony ships. An alien attacks! A meteor strikes the ship! All but one of the plants are destroyed, and that one is damaged! What will they do? Will the colony survive? The ships's horticulturalist was captured in the attack--will they be able to get him back? Can his daughter, who's angry at being ripped away from all her friend back home, decode his notes and heal the plant? Watch the drama unfold!!!


The testes have a muscle called the cremaster, that pulls them up whenever it's too cold to maintain the right temperature for spermatogenesis (the process which sperm cell are produced), or relaxes to cool the testes whenever it's too hot. Have this process be a lot more temperature dependent, working only when the testes are around the temperature of the body.

The cremaster muscle should not be an independent muscle, or involuntary. It should be a voluntary act to contract or relax it, depending if you want to be fertile or not. In this system, you need to pull the testes in advance, maybe some hours prior to sex, in order to have functioning sperm cells.

Although you'll have no chance of conception, semen will be produced normally, as the majority of its components is not produced in the testes, but on different locations of male genital tract.


Look to the bladder.

The male urethra has two purposes: the ejaculation of semen and the elimination of urine. For most men, these two functions are mutually exclusive; it is difficult to maintain an erection with an extremely full bladder, and urination becomes very difficult when a man has an erection.

Brief anatomy lesson: the urinary and reproductive tracts meet inside the prostate gland, which surrounds the urethra and rests directly below the bladder. The vas deferens carry sperm from the testicles to the prostate, where they merge with the seminal vesicles and join with the urethra via the ejaculatory ducts.

Downstream of the prostate lies the smaller bulbourethral gland. Human urine is acidic and poses a threat to the health of sperm. The bulbourethral gland secretes a slightly alkaline fluid, often colloquially referred to as "precum", which neutralizes the urethra prior to ejaculation. Semen itself is also slightly alkaline in order to neutralize the natural acidity of the vagina.

I can think of two ways that we utilize the confluence of these two systems to achieve the desired effect:

  1. Males of your species are capable of urinating and ejaculating simultaneously. If the urine of your species is sufficiently acidic, it will kill the sperm before or shortly after they leave the penis.
  2. Males cannot urinate and ejaculate simultaneously, but can choose to urinate at any time and the act of urinating forcibly closes the ejaculatory ducts. In my opinion, this is the more reliable and realistic solution, since the closing of the ducts would prevent urine from entering the vas deferens where it might damage future sperm. However, the sperm would probably leak out afterwards, so caution would need to be exercised in order for this to be truly effective.

Just rewire the brain.

Ejaculation requires muscles to move. Remove those muscles from autonomic control based on emotional state. Provide that control to the motor cortex in a similar fashion to moving a finger.

To explain why:

  • Moral, it is unseemly for a man to not control this. Those that can't are shamed. Many young boys undergo the therapy/procedure as babies/children because there parents wish to avoid future shame.
  • Political, an edict by the government forcing boys without the genetic mutation to be killed. Maintained for numerous generations has left the population mostly/entirely in this state.
  • Evolution, controlling this provides a cost/benefit. Perhaps the smell attracts the wrong kind of predator, or disease. Perhaps the capacity to remain virile reduces quickly with proportion to ejaculation.

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