When the humans start mating on my generation ship(so after survival training), there should be at least 100 pregnant women as a result. I mean per 1000 women in the united states that are married there are up to 114.1 pregnancies which is close to my minimum of 100. I mean ideally the majority of the women should become pregnant but even a minority is significant.

Now first, I thought that nocturnal-diurnal pairs shouldn't be allowed to avoid emotional upset from 1 person being tired and the other wide awake. But then my momma told me that I could allow a nocturnal person and a diurnal person to mate during the small overlaps(so twilight).

Now the nocturnal people don't get any less sleep or less quality of sleep so you don't need to comment on that.

What I am trying to decide here is whether or not the people should be monogamous or polygamous.

Case 1: Monogamous

This is what I favor and what my momma favors. Sure you might get a low reproduction rate with monogamy but so what? For one thing, monogamous doesn't mean you can't be with your friends 1 day and your partner the next. As long as you mate with 1 and only 1 person during a given period of time(breeding season or lifetime(so you might mate with 1 male during 1 cycle and a different male the next cycle, that is considered monogamous, it doesn't have to be for life)), you are monogamous.

Another reason I favor monogamy is that the lower reproductive rate means more care per child and it also means that population growth doesn't explode.

I mean let's say that the population is in stage 1 population growth. It does grow and it seems explosive given that the birth rate is super high. But the death rate is also super high. In stage 2 however, death rate dramatically drops while birth rate stays about the same so the population growth truly becomes explosive at this point. This stage 2 population growth is not wanted on a generation ship. But death rate should be low(or is wanted to be low) and birth rate should be higher at all times on a generation ship(after all the purpose of a generation ship is population growth while in space).

Here are a few things that the people and aliens would have to worry about if they are in a stage 2 population situation(medical care is very reliable on a generation ship):

  • Pernicious Anemia(B12 deficiency and Folate deficiency)
  • Iron deficiency Anemia
  • Scurvy
  • Dehydration
  • etc.

Along with the already existing deaths from illness, injury, old age, etc. they would have to worry about people dying from thirst or nutritional deficiencies. This explosive reproduction and worrying about a high death rate would be less likely to occur if the people are monogamous. This is why I favor monogamy. Plus our society forces monogamy and human polygamy is, at least in developed countries like the US, not allowed by the law.

Case 2: Polygamous

This I am against, not only because it is forced out of human society but for several other reasons.

1) The population growth is going to be explosive and there is going to be a really high death rate because of that(lower than birth rate but still high, too high for a generation ship).

2) Inbreeding is going to be super high. In a monogamous population, you have double the action against inbreeding(so in other words, son can't impregnate mom, sister cannot be impregnated by brother etc. in a monogamous population because not only is the mom against it but so is the dad). In a polygamous population however, to keep inbreeding low, the aliens would need to do maternity and paternity tests(in other words a lot of genetic testing) before a MF pair(male female pair) even thinks about having children and if the MF pair has any kind of genetic similarity whether it be sibling type of similarity(both parents the same) or the father being the same or the mom being the same, they wouldn't allow that pair to breed. But there is 1 problem with this. They would have to test all the moms genetically and all the dads genetically as well because there is a chance that 2 moms or 2 dads could be twins. And identical twin moms and identical twin dads would mean testing of the older people past reproductive age to see if any of them had identical twins.

So polygamy is not good from a sociological perspective(monogamy is the norm nowadays in most places) or from a genetics perspective(lots of testing just to see if the MF pair has the same mom, same dad, same parents(both), or whether the similarity is further back at grandparents and great-grandparents etc.) and just too much testing and thus inbreeding will happen and could lead to a massive population decrease if it continues on like this. It also isn't good from a whole "generation ship is for population growth" perspective.

So I think I should keep my starting number at 5000 and starting male:female ratio at 1:1 and have my humans be monogamous.

But are there any benefits to a polygamous population or is it all just risk after risk after risk? And are there any risks with a monogamous population other than the normal causes of death I described earlier(which isn't that big of a risk on a generation ship)


closed as unclear what you're asking by Mołot, Erin Thursby, Hohmannfan, kingledion, Werrf Dec 27 '16 at 17:40

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    $\begingroup$ I'm confused. Your sociological setting is "men and women barely meet to procreate because they're on opposite shifts all the time?" That and it sounds like your monogomists are puritans while your polygamists are just a bunch of horny rabbits. $\endgroup$ – Cort Ammon Dec 26 '16 at 20:39
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    $\begingroup$ There is literally no reason to get genetic testing to determine if you have the same mom. I think she'd remember. Like if two kids came out of her and she raised them. They also might remember that time they grew up together, in the same house. I don't think you understand what polygamy is. $\endgroup$ – Erin Thursby Dec 27 '16 at 0:04
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    $\begingroup$ It's not clear why you think that polygamy leads to inbreeding, except maybe for some videos on youtube. Nor why you think breeding rates would be any different. Results for isolated "clans" in a generally monogamous society won't match up with results for an entire society. But with a 1:1 M/F ratio in a closed environment, monogamy seems the likely structure just to keep the peace overall. $\endgroup$ – user2338816 Dec 27 '16 at 1:25
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    $\begingroup$ @user2338816 The OP needs to do more research on polygamy, for sure. $\endgroup$ – Erin Thursby Dec 27 '16 at 2:41
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    $\begingroup$ Downvote because the question is good but it seems unnecesary long, adds confusion with the diurnal/nocturnal cycles (from other questions) and it's plagued with (I'd say false) assumptions, which bias the answers. Please, edit. KISS :) $\endgroup$ – xDaizu Dec 27 '16 at 12:16

If your people understand that they are in a generation ship, 100% of your population issues will go away unless you suffer mass rebellion. Such mass rebellion will have little to nothing to do with your ship's approach to sex and child rearing.

An excellent example of this is the Aboriginal cultures of Australia. In many of them, while a child was between one man and one woman, the timing of said child was not theirs at all. It was up to the elders to decide when the land could support another mouth to feed. The ability to maintain this had very little to do with monogamy/polygamy and everything to do with their understanding that they were in a fragile little generation ship of their own with very limited resources and a long term goal.

Sex and child rearing is a major factor of societies, so you will typically find the choices made were intimately entwined with their entire social structure. If you're comfortable writing about societies similar to Western culture, stick to monogamy. However, there are plenty of interesting counter examples throughout time. One interesting example comes from the Amazon where a particular tribe had a curious approach to making children. When a woman decided she wanted a child, she would sleep with every strong able-bodied man in the tribe, with the theory that that would make a strong child. Their theory may not hold much water according to modern science, but it had a very important social effect: none of the men knew if the child was theirs. Accordingly, every child was raised as "the tribe's child," and the child was never short on attention because everyone raised the child as their own. Their entire social structure was entwined around this approach!

There are many variants of having multiple partners (I'm assuming you were not only referring to polygyny but also polyandry and the many other variants). Each of which has their own nature. Some center around one man and many women. These are often designed for high birth rates, as you say and are popular when the lifestyle of the culture results in a large number of early male deaths. Others which are more fluid with relationships focus on minimizing jealousy and avoiding the feeling of a partner being "property."

This also highlights the biggest risk for monogamy: a feeling of ownership that often is associated with that approach. If parents are injured or fall ill, it's easy to say "it's not my kid, not my problem." This issue is prevalent enough that it would come as no surprise to see that many cultures have developed solutions to minimize this risk (such as the strong extended family or a religious edict to help orphans in need).

If your generation ship is finding that this concept of ownership is starting to fester in their society, they might look more towards the poly relationships as a way out (or they might take any one of a hundred other solutions, because they're out there). Likewise, a society with gender-specific roles where the male roles are highly dangerous (and lead to large numbers of fatalities) may naturally drift towards polygamy. On the other hand, a poly culture might choose to start going towards monogamy if they find that the looser culture is failing to properly support for the children, letting them slip through the cracks. If the children need 2 concrete parents that they can rely on, the relationships will adapt accordingly.

But, no matter what, these decisions are going to be made with awareness of the fragile bubble surrounding them. Whether they choose monogamy, polygamy, polyandry, or even a pure artificial birth process, they're going to make those decisions with an understanding of the climate around them. You won't see huge ballooning populations like you worry about, because the world they live in is too visibly fragile to make mistakes like that.

  • $\begingroup$ Good answer, but I'm sometimes unsure whether you're using Polygamy (multiple spouses) to mean Polygyny (multiple wives). $\endgroup$ – Pahlavan Dec 15 '17 at 8:02
  • $\begingroup$ @Pahlavan I believe I am using polygamy correctly. Why do you think I am focusing on polygyny? $\endgroup$ – Cort Ammon Dec 15 '17 at 14:29
  • $\begingroup$ I believe it was the "only refering to polygamy but also polyandry and the many other variants" part that triggered the reaction, but going over the post again I was being too sensitive there. Maybe I came with that impression from another post and it carried over. $\endgroup$ – Pahlavan Dec 15 '17 at 18:02
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    $\begingroup$ @Pahlavan You know, you're right. That's a mistake in my word choice. I've edited it to fix that. $\endgroup$ – Cort Ammon Dec 15 '17 at 19:15

There's all kinds of weird coming off this question, as well as lots of extraneous stuff, so that's why folks are having a tough time answering/have voted to close.

Polygamy might not lead to inbreeding. It completely depends on how your system on polygamy works. Because, surprise! There are many different kinds of polygamy. (Multiple wives, husbands, rotations seasonally...)

Also, I don't think you are clear on the definition of polygamy, which is:

po·lyg·a·my pəˈliɡəmē/ noun 1. the practice or custom of having more than one wife or husband at the same time.

The way you are talking about polygamy, it's as though you are talking about open relationships, or no marriage at all. Just willy-nilly sex. You say this of Monogamy:

son can't impregnate mom, sister cannot be impregnated by brother etc. in a monogamous population because not only is the mom against it but so is the dad

Implying that the second you open the door to polygamy, sons will be porking their moms, sisters will be sleeping with brothers AND the dads (aka the husband of the mom) will be all for it. Which means you might not fully understand polygamy.

My suggestion is that you actually research how it works.

If one guy is married to 6 women, all the kids they have are his. That's easy. But if it works the other way--like one lady and multiple gentlemen--that's much harder to track. But yeah, it CAN be tracked, depending on what your rules are (and I would think that it would have to be) and you likely would not need genetic testing as long as you kept records.

At one point you actually say that people would need genetic testing to determine if they came from the same mom. Which...think about that for a second. Most women don't forget having a baby. And most people recall the people they were raised with.

You also seem to be indicating that children will not be well cared for by polygamists. In fact, societies that have practice polygamy will often have an "it takes a village" mentality where everyone helps raise the kids. Really depends on the families.

The question was pretty convoluted and a lot of the premises you're basing things on seem incorrect, incomplete or not understandable (by me anyway).

I am not going to cover the disadvantages, because you didn't ask for those, but here are, in this situation: The Advantages to Polygamy.

It provides a better support system. Because polygamous families will have more wives and more children, members will always have someone to talk to. They will have a shoulder to cry on, someone who they can relate to and a confidant. This can lessen or eliminate the risk of depression among the members, especially the children.

Similarly, when it comes to doing chores, there will be more hands to help around the house. Tasks will be split among members, lowering stress at home.

It guarantees financial stability or pooling of resources . Wives and grown children can earn money by working outside the house. The household will then have more income, which can be shared by everyone. When a bunch of people live to together and pool their resources, it can be a tremendous advantage.

It can help to prevent adultery. Because all spouses will have consent, then there is no extra-marital to hide from your partner. This reduces adultery to a non-issue and prevents the temptation of cheating on your spouse. From the genetic standpoint this is outstanding, because, seriously, your monogamy model assumes that one one will stray. If they do stray, whatever kid they have will not have the correct genetic info attached to them. If Huband X cheats on his wife with Lady Y, who is married to Husband Y, their kid will be recorded as being the kid of Husband Y. Leading to inbreeding. People are people, and although monogamy is nice on paper, cheating is a bit more likely than it is in a polygamy system (not to say polygamists never cheat, just saying it's less likely they'd HAVE to).

If instability is introduced into the system, Polygamy can help keep population numbers up Right now you have a nice, neat 1:1 ratio of M to F. Should that ever change, should the mortality rate go up, polygamy is your best bet. In your premise you say that polygamists/polygamous societies have a high mortality rate. That's true, most do. THERE'S A REASON FOR THE CORRELATION. It's not that polygamy CAUSES a high mortality rate. It's that it's advantageous for humans to be polygamous when there's already a high mortality rate, thus the correlation. Pretty much if things are out of balance ratio-wise, or your death rate spikes, guess what, monogamy loses many of its advantages.

Some men have good genes... some males may have much better genes than others which is particularly important for populations where there is a heavy load of diseases and parasites to which resistance is genetically heritable. In space/the ship there may be other dangers. If one male holds the genetic key to resisting a particular disaster or radiation, then the fact that he had a whole passel of children might be good rather than bad or it could introduce a weakness to a lot of the population. Welcome to the genetic lottery!

Half Siblings Reduce Genetic Relationships See Brythan's answer, this edit/addition is fully inspired by that!! Props! Half sibs are less related than full siblings. And that's going to happen a lot in a polygamous population. With monogamous breeding, full siblings, with genetic material that matches up from both mom AND dad, will happen more often. This means that in a polygamous situation there will be a lot less full cousins, and a lot of 1/2 cousins. Two children born of a poly marriage from two different mothers are actually LESS related than two children born from a monogamous marriage. When those 1/2 sibs each have children of their own, provided they have married different people (and don't have the same husband or wife) their offspring will actually be less related than the offspring of monogamously produced kids. Not to say polygamy will result in less chance of genetic defects overall (it absolutely won't) but it is something to consider.

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    $\begingroup$ Thanks for pointing out the false assumptions, it eliminates the need for me to answer. However, I must point out a few things. Multiple husbands is polyandry, not polygamy. Also, a problem in some polygamous societies is shutting out males. Polygamy works when there is a surplus of women compared to men. The next generation will have a roughly equal female to male distribution. If polygamy then continues, that means that you will have a majority of men who will remain single, and a minority of men with the majority of women. This will reduce the genetic diversity of your generation ship. $\endgroup$ – Xandar The Zenon Dec 27 '16 at 3:44
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    $\begingroup$ @XandarTheZenon Depends on where you go for your definition. Sociologists and many dictionaries refer to polygamy as any multiple spouse situation, but the strict definition is, yes, what you say. Since the OP seems to have some...misinformed ideas on poly in general, I didn't bother with that part of it. $\endgroup$ – Erin Thursby Dec 27 '16 at 4:32
  • $\begingroup$ @ErinThursby Okay. I always preferred denotations anyway. On a different note, my Hawaiian friend uses Poly to mean Polynesian. $\endgroup$ – Xandar The Zenon Dec 27 '16 at 4:56
  • $\begingroup$ @XandarTheZenon LOL. $\endgroup$ – Erin Thursby Dec 27 '16 at 6:26
  • $\begingroup$ @ErinThursby What are the DISadvantages to Polygamy? $\endgroup$ – JohnWDailey Dec 27 '16 at 17:34

Polygamy reduces the founder effect

A problem with a small population from which all mates come is the founder effect. The basic issue is that if each couple only has two children, they will only have some of the parents' genes. Each child has a one in two chance of getting a particular gene (assuming that it only appears once in four opportunities in the parents). So one in four times, neither child gets a particular gene. If that parent is the only carrier, that gene is lost to the population.

You can fix this by having lots of children and mixing and matching breeding partners so as to maximize the chance of good pairings. I.e. two parents may be incompatible at a particular gene. For example, a mother with blood type genes of AO and a BB father. Half the time the children will be BO, which will cause problems with an AO mother. Blood type is of course easy to check, but other issues may be less visible.

Of course, in your situation, you don't want to have more children than parents. So you need some other kind of solution to this. As such, monogamy is probably good enough genetically. If anything, you may want to do something like mandatory sterilization and then use in vitro fertilization (IVF) to produce children. That would provide stronger population controls. It would also allow for better genetics at the destination if you can still use the original genetic material.

Note that frozen genetic material currently has a shelf life that wouldn't work for a generation ship.

Anyway, that's the positive impact of polygamy. In an increasing population such as exists after landing, polygamy best preserves the existing genetic diversity. It's going to be less helpful on ship though.

It's also worth noting that in your original terminology, you can still implement this within your monogamy. Each successive pairing can be monogamous until the baby is born and then each could enter pairings with new partners.


After twelve generations maintaining a population of 4096, everyone will be related. The math is relatively simple. Start with 4096 people who are not related. Everyone has two kids with one partner. Now you have 2048 pairs in the next generation who are not related, although each member of the pair is the sibling of the other. If you do this repeatedly, you will find that in the twelfth generation, everyone is at least a twelfth cousin (many will be more closely related). You can no longer reject matings between related people. That's going to be true even without polygamy.

Polygamy will make this happen quicker, but it also reduces the relationship. Half siblings are less of a genetics problem than full siblings, and that relationship also decreases as the number of generations increases.

Of course twelfth cousins aren't exactly close. Second cousins can marry pretty much everywhere. It's first cousins that may be restricted. The greater problem is going to be the loss of genetic diversity over time.

To avoid inbreeding, you will need to pay attention in polygamy or monogamy. The limited options on the ship make it important either way.

  • $\begingroup$ The half-sibling thing does reduce the relationship. I think a blend or directed breeding might be the answer. So if you genetically test a male, who is least related to everyone, or has the best genes for survival or a particular genetic marker, why not assign that guy multiple wives--or leave it up to the population. When it was legal the percentage for polygamy was only 20-30% for Mormons. $\endgroup$ – Erin Thursby Dec 27 '16 at 17:08
  • $\begingroup$ Either way, it's got to be tracked--in the same way fertility clinics do. Even though you might not be related closely, you might both carry a genetic defect that you would not want passed down. $\endgroup$ – Erin Thursby Dec 27 '16 at 17:09

Why don't you simply decouple procreation from recreational sex? The people on the ship don't need to be "married" (whatever that means in such a context) in order to have children. Women must have children because it's a social imperative; the children are obtained by artificial insemination according to the algorithms run by the ship AI. (For a well known example of such a practice, albeit with lower technology, see Lebensborn.) What men and women do in their free time is up to them.

  • $\begingroup$ I view artificial insemination as inferior to natural conception. Sure you might get more pregnancies this way but you have to keep the sperm at just the right temperature and know right when the fertile window is and for 2500 women or more, that is hard to keep track of menstrual cycles. Males have what they need to keep the sperm at the right temperature and while they don't know the fertile window unless the women tell them, still, it is stimulating and there is a chance of pregnancy anywhere from 5 days before ovulation to 5 days after ovulation so ovulation date isn't super important. $\endgroup$ – Caters Dec 26 '16 at 23:03
  • $\begingroup$ @Caters: Then do it the old-fashioned way. And women know when they are fertile and should come to the Life Fountain center to become pregnant. I just think that traditional marriage and a generation ship don't mix well. $\endgroup$ – AlexP Dec 26 '16 at 23:05
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    $\begingroup$ @Caters If you're already on a generation ship, storing sperm and tracking that information seems like it would be trivially easy. $\endgroup$ – Azor Ahai Dec 26 '16 at 23:43

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