In the year 21--, a crew of 100 sets out from Earth on the good ship Tenzing Norgay, bound for Epsilon Eridani. The journey is estimated to take . . . well, quite some time, given that it was calculated that the time spent to engineer a significantly faster propulsion system (compared to the technology of the day) would negate the benefits of going at the faster speed, and would end up costing too much more.1 This means that the crew is stuck with using a ship outfitted with the Rockaway Plastopedic ThrustomaticTM 2 engines, making the trip take at least 250 years - far more than twice the lifespan of a normal human. It was also decided, to the crew's dismay, to not pursue suspended animation technology, thanks to budget cuts.

The one thing that the make of the ship did foresee was that a future generation might not be too happy about having to live and die in a ship, without ever stepping foot on a planet or doing anything besides get ready to reproduce and die. There is a very real threat of a person (or a group of people) hijacking the ship some day, and moving it to some nearby system. The computers are always on autopilot, but there's always a way to hack them.

The government decides to go with a foolproof method: using genetics to make sure that future generations on the ship will not rebel, using in vitro fertilization onboard via automatic systems. This is all very well and good, but I, the creator of the story, need to come up with a plausible explanation. I can imagine a few ideas, but they're not too good; they all boil down to neural modifications - changing genes to influence the brain. I'm no neurologist, but this doesn't sound feasible.

How can genetics be used to quell a rebellion before it begins?

1 Please, please don't dispute this. I think I can find a way to justify this, no matter what objections are made.
2 The Rockaway Plastopedic Thrustomatic is a trademark of Rockaway Blastopedic Industries, soon to be of Epsilon Eridani.

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    $\begingroup$ I'm not good enough on neuroscience to actually answer your question. But a new generation comes about 20-25 years. So 250 years are, at least 10 generations born on-board the ship. The required skills to hack the system are probably hard to come by in a confined system. Furthermore the Space is mostly empty, even if you could, where would you go? No, I'd be more worried that they decide to STAY in the ship starting from the 5th of 6th generation. And how is the birthrate planned? 100 people ranging from 25 to 65 years old. So about 25 women who can bear children. You could end with 5 people. $\endgroup$ – clem steredenn May 24 '15 at 22:37
  • $\begingroup$ @bilbo_pingouin I'm imagining that they're taking a route near enough to other stars that it would be possible to turn the ship to a different destination, closer at a given point than the intended one. Hacking would be hard to come by, but some crew members would have to be computer-savvy, to some degree. Regarding birthrate - non-human birth has been perfected (i.e. machines can essentially give birth) - that's for another question, though. $\endgroup$ – HDE 226868 May 24 '15 at 22:41
  • $\begingroup$ And why would they want to leave the ship? They don't know anything else. Some crew might be computer-savvy, but maybe not enough to understand how the protection was done. And you can't have an AI ensuring that they do not try to use evolution to recreate the appropriate knowledge? $\endgroup$ – clem steredenn May 24 '15 at 22:50
  • $\begingroup$ @bilbo_pingouin Like I said, they would rather go somewhere nearer, where they could actually reach a star system, as opposed to journeying through space for their entire life. And the voyage lasts for 250 years. Odds are that someone will find a way to hack the computer. $\endgroup$ – HDE 226868 May 24 '15 at 23:04
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    $\begingroup$ 100 people sounds awfully small. Don't forget your effective population size, especially after a few generations of inbreeding... $\endgroup$ – user May 25 '15 at 11:33

The problem with genetic modification isn't going to appear during the trip, but rather once they reach the destination. A group which has been modified or selected to be docile and relatively apathetic is not going to be the best choice of people to deal with unknown and potentially dangerous colonizing situations.

Face it, humans being tough and pretty ornery is the recipe for our evolutionary success despite ice ages, sabre tooth tigers, mega volcanoes and pretty much everything else that has been thrown at us to date. What you really need is some way to redirect that sort of aggression and problem solving ability without wreaking the ship. While you might get a large fraction of people zones out by having an on board FaceBook server, you would probably need something more constructive.

I would suggest some sort of VR "game" which is based on the sorts of observations and knowledge available to the designers before the ship set off, to allow people to "train" for the day the ship arrives. Each generation gets more detail as the ship approaches the target and more detailed observations and information gets added to the "game". If there is the space available, a "holodeck" sort of arrangement can also be added for some real life physical training action as well.

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    $\begingroup$ This seems the most reasonable answer: don't fight it, because it will be needed later; just give it some other, safe outlet. Heck, why not have a place (some sort of forum, perhaps?) where people can ask questions and get answers on hypothetical scenarios, to get them to think through various eventualities, and give them a creative outlet at the same time? You could additionally award some sort of points for good contributions, and detract points for bad contributions. These points could perhaps also translate to having various privileges on the forum itself. $\endgroup$ – user May 25 '15 at 11:29
  • $\begingroup$ RE: "Once they reach their destination" -- If you make the docility is non-permanent -- (i.e. just put lithium in their water) -- this problem goes away. (i.e. when they hit their destination -- there will no longer be lithium in their water, they will stop being docile.) -- +1 for VR game though. :-) $\endgroup$ – BrainSlugs83 Feb 9 '16 at 21:09
  • $\begingroup$ @BrainSlugs83 If the children have no exposure to people who are not docile, wouldn't they have no chance whatsoever to adjust to the sudden lack of docility in both themselves and their peers? $\endgroup$ – rytan451 Jul 14 '17 at 11:58

Rerouting isn't an option for non-fantasy engines

For all currently feasible propulsion options and realistic physics, movement doesn't require energy, but acceleration does. A trip from A to B spends half of fuel/energy accelerating and half of it decelerating; and the fuel/energy amount spent influences only the speed, not how far they will go. Boring, but with rather interesting implications.

  1. A simple stop in the exact middle means that you need twice as much fuel/energy than a non-stop rule. Which you likely don't have, since fuel is most likely 90%-99% of your ship mass, and taking double fuel isn't really an option.
  2. Once you have done the main acceleration, the course is pretty much set in stone, and you'd only have enough fuel to stop. If the colonists rebel and reprogram the computer, the only thing they can do differently is either to stop elsewhere along the same line - in the middle of empty space, or alter the course to some other location where they'll only be able to stop by crashing into it at Ludicrous Speed (tm), annihilating the ship and possibly causing something similar to the dinosaur extinction event that happened on Earth.

Of course, a story can make different rules, but these can cause interesting situations even without deviating from reality.

  • $\begingroup$ If only they would've stopped at the chemists for a bag of peanuts first, they could've told them just how mindbogglingly huge space is, and how that's a Really Bad Idea (TM). $\endgroup$ – Mazura Oct 12 '17 at 21:23
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    $\begingroup$ Theoretically, some good piloting can decelerate a spacecraft using gravity assist. It might take quite some time, but if the crew is determined... $\endgroup$ – Olga Oct 13 '17 at 0:00
  • $\begingroup$ The gravity-assist stop is highly dependent on how many orbiting bodies you have to play with as well. The book Aurora went into detail about this (handwaved to a degree so that it wasn't technical), but there came a point when the ship's AI could not calculate an intercept with another massive body with the remaining fuel on board. The ship had slowed down enough that the humans on board were able to disembark (albeit with still dangerous levels of deceleration) before it went on its merry way out of the solar system. Mind, it spent 50+ years doing this: the n-body problem is HARD. $\endgroup$ – Draco18s no longer trusts SE Dec 22 '17 at 18:49

Genetic control

The first matter to deal with is to ask what level of genetic modification is possible. If we are limited by standards slightly more advanced than today's, then we have a few options. We can..

Reduce or remove the production of certain catecholamines, deflating some riot situations.

Reduce or remove the production of serotonin, causing memory loss. (What was i angry about?)

Modifying the image of a "perfect being." More specifically, giving a genetic bias towards a certain leader figure. Studies have shown that completely irrelevant genetic traits have contributed to public image. So what if the perfect match happens to be the current ship captain.

Kind of genetic

There is the ability to genetically hamper the supply of insulin to artificially administer diabetes. This could very quickly nip rebellions in the bud if the only insulin supplies are located at secure nodes.

In the same way, albeit somewhat less cruel, get everyone on a certain drug and watch as rebellions struggle through withdrawal before crawling back in surrender. (Never mind, just as cruel)


Rather than using genetics (a recipe for some resistant hero to arrive), use neuroscience. As soon as someone gives birth, transport the newborn to a government approved "educational" site, guaranteed to improve IQ by looks in PR folder 20%. What is actually happening is basic conditioning. While curbing any rebellious thoughts for the next 2-3 years, the young will be fed direct associations between rebellion and pain, and conversely be given compliance and reward. As an added bonus, anyone audacious enough to not put their newborn through this liberating process will have the child labeled as being in possession of a lower intelligence.

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    $\begingroup$ I think that "other" part is the most realistic. Some studies show that observing the behaviour of kids in their first years, together with DNA studies, indicate a probability that they could turn violent. A la Minority Report. This is probably the safest route, assuming those techniques have improved. $\endgroup$ – clem steredenn May 25 '15 at 6:48

Harry Harrison's Captive Universe had an interesting approach to this: Split the population into two separate groups, engineered for low intelligence / docility , not allowed to interbreed during the voyage, but set up so that when they're allowed to interbreed on arrival, the children will have normal intelligence. The passengers don't know they're on a generation ship, and the crew had a monastic culture designed to discourage changes.

(see https://en.wikipedia.org/wiki/Captive_Universe)


Why not make them intellectually disabled? The crew aren't exactly crew. they are more like cargo. They aren't necessary for maintaining the ship or directing it, they just need to sit quietly and not make a mess. So, make them docile simpletons. Mild intellectual disability will allow them to eat and reproduce and not much else. They won't have the ambition or the ability to redirect or destroy the ship. We know of lots of genetic disorders that cause intellectual disability. Down's syndrome could be used, or perhaps William's syndrome since that specifically impairs visuospacial reasoning. Once you reach the destination you can fix the disorders in the new children and have a normal colony. Just remember to round all the sharp corners on the ship and put child safety locks on the airlocks.

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    $\begingroup$ But when they get onto the planet, how will they survive? $\endgroup$ – Jimmy360 May 25 '15 at 8:26
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    $\begingroup$ @Jimmy360, they don't need to survive on the planet, the disabled humans are only breeding stock. They are the biological component of a colonization machine, intended to provide a cheap method to give birth to the "colonists", who are the last generation (pre-touchdown) of humans to be born on the ship, from the bank of alread-fertilized eggs to be implanted into female breeders. (For that matter, why include males at all?) $\endgroup$ – ghoti May 25 '15 at 13:28
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    $\begingroup$ Anyway, I'd expect that whatever "affected" humans were still alive at colonization time to remain on the ship after colonization. The change of environment would be enormously stressful for them, and the ship would be a reasonable old folks home. $\endgroup$ – ghoti May 25 '15 at 13:31
  • $\begingroup$ This will not work since intellectually challenged colonists will not be able to raise fully-functioning children. Machines cannot replace humans as caregivers unless they are indistinguishable from humans. But then, why bother with human cargo in the first place? Just vat-grow humans once a colony is established and ready for fragile organic beings... $\endgroup$ – Olga Oct 13 '17 at 0:04

Why bother with genetics? Instill the importance of the mission into future generations with education. Raise it to the level of religion if necessary. It's certainly cheaper.


If you are firmly set on using genetics, you can take a look at novelty seeking and associated genes.

Novelty seeking is a personality trait associated with behaviours you want to restrict in your crew: curiosity, asocial attitudes, risk-taking, impulsiveness. People who demonstrate low levels of novelty seeking are perfect working bees. They tend to have highly developed conscientiousness, high preference for risk aversion, and introverted behavioural patterns. The downside is that they are less creative or flexible.

There is a caveat. Novelty seeking is important for psychological well-being and overall satisfaction with life. Therefore, you cannot get rid of it completely.

There is some evidence that novelty seeking is linked to the Dopamine receptor D4 gene on chromosome 11, specifically the length of its alleles. If you find a way to regulate this you might end up with a perfectly suitable colonist: Not too adventurous, but not docile either.


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