Earth is dying. We mis-managed it and brought the whole ecosystem to the edge of total collapse.

About 50 years ago, we decided to move humankind to another planet, and now we are almost ready. A big, multi-generation ship is in orbit around Earth. It will hold a billion lucky people.

The rest of humanity will be left back on Earth to their fate.

This ship will reach an Earth-like planet in about 1000 years. Once there, genetic engineers will breed domestic animals in artificial wombs.

Now, our team of psychologists and engineers are dealing with this question: What about having some pets on board?

It makes total sense to keep some pets on board, to keep people generally happy before we get there. But we have several constraints:

  • The animal should consume as few resources and produce as little ... ahem ... waste as possible
  • It should be generally likeable, well received by kids. But also:
  • Should be religiously neutral

Muslims have a saying: "unholy dog" and some Christians are against cats, because black cat... you know it. Hindu people hold cows sacred.

This is why we have to engineer a completely new animal to accompany us on the journey.

We have advanced DNA-replicators and we can manipulate DNA as we like. While playing with human DNA is rejected and outlawed by all, we still can put our imagination to work with animals.

So, how should such an animal look? (How big? What color?) And why?

P.S.: The ship itself maintains 0.95 G by rotating itself, so you can assume Earth-like conditions there. Also, the population is composed of "generally rich" people of all races and all religions.

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    $\begingroup$ The waste is not an issue, assuming that you also have to process human waste. $\endgroup$ – user3106 Mar 11 '15 at 10:24
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    $\begingroup$ Digital (virtual - possibly holographic) or robotic pets would probably be chosen rather than biological pets. $\endgroup$ – Scott Downey Mar 11 '15 at 11:48
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    $\begingroup$ I'm not aware of any Christians who object to cats. Perhaps that's a cultural thing. $\endgroup$ – superluminary Mar 11 '15 at 15:04
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    $\begingroup$ Tribbles, of course. $\endgroup$ – Adam Davis Mar 11 '15 at 18:05
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    $\begingroup$ The ship's internet will not work without cats. Take cats. $\endgroup$ – Oldcat Mar 11 '15 at 22:48

12 Answers 12


Normal Pets

If you're looking at sustaining a billion people for 1,000 years, you don't need an artificial life system on your ship. You need a full, 100% working ecosystem, transported from Earth's remnants with as many animals, insects and plants as possible.

Artificial life systems are fragile. They have relatively few failure points, and they require extensive maintenance. You're better off trying to get a real ecosystem going, exactly the same as what happens on Earth. You can help support it with artificial devices, but in general this will give you a lot more depth to your life support - it's much harder to accidentally break a functioning ecosystem. Having all the animals and plants gives it an ability to absorb disasters or malfunctions that artificial systems will lack.

Because of that, you'll want to have as many different pets as possible, because they help contribute to this system. You will need to regulate and control their numbers, but restricting everyone to a single, artificial pet will actually hurt you, not help. On top of the above, it makes your entire pet population vulnerable to a single disease vector.

Regarding Religion: You have a ton of space on this ship. People are going to be capable of moving if they have neighbors with pets they object to. More than that, you will absolutely need these different groups to be willing to get along, and someone who will object to someone else's pet on religious grounds is a bad choice for your generation ship in the first place. Someone who will object over their neighbor's dog is the same person who will object to other things, and you absolutely can't afford the kind of conflicts that kind of intolerance could breed.

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    $\begingroup$ But that begs the question: If we can build a fully functioning fake ecosystem... If our technology is advanced enough to build a habitat that supports a billion people for a thousand years... why not just fix our natural one? why not build one that sits opposite earths orbit and save the trip? Why not build multiple in orbit, one for each religion? Multiple ships for the trip - 100million on each ship-, one for each religion, so that each ship can have its own "pet" of choice? but... I may be going off on a tangent :) $\endgroup$ – WernerCD Mar 11 '15 at 17:46
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    $\begingroup$ @WernerCD: It looks like the comment got deleted, but originally there was a reference by the OP that Earth was essentially "depleted" to create this super-ark. But yeah, I agree that in general the technology required for a billion-person ship is such that fixing the planet should also be possible. $\endgroup$ – Dan Smolinske Mar 11 '15 at 17:53
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    $\begingroup$ @WernerCD Totally agree, but building domed cities right on Earth would be better than going to orbit. It should be impossible to devastate our ecosystem so badly this planet is not more habitable than space. (Things like gravity, pressure, free supply of volatiles like water, nitrogen and oxygen...) $\endgroup$ – Ville Niemi Mar 12 '15 at 11:03

I would think that if people have issues with 'dogs' or 'cats' or what have you for religious reasons, I would say they would also have an issue 'creating' a biological animal just for our 'amusement'.

So because of that, I would recommend: Rabbits, eat little, waste little and have a large 'cute' factor. They even are edible in a pinch.

EDT To add for the 'creature-design': Add a gene to make the bunnies glow in the dark, they could have different colors. They could also act as 'night lights' for young children and emergency lighting!

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    $\begingroup$ @James They're real theguardian.com/world/2013/aug/13/… $\endgroup$ – Scott Downey Mar 11 '15 at 14:23
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    $\begingroup$ @ScottDowney That's amazing...and somehow seems both awesome and wrong at the same time. $\endgroup$ – James Mar 11 '15 at 14:29
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    $\begingroup$ Just make sure to include some holy hand grenades in case of any mutations (and of course, instructions that walk you through proper counting and throwing procedures, lest thou count to four or five.) $\endgroup$ – WernerCD Mar 11 '15 at 17:35
  • $\begingroup$ Rabbits are not religion-neutral. Jews can't eat rabbits. $\endgroup$ – Mr Lister Mar 12 '15 at 10:37
  • $\begingroup$ @MrLister the OP is asking for pets, not food ;) $\endgroup$ – algiogia Mar 12 '15 at 13:28

Mass must be conserved

If you are constructing a ship large enough to carry 1,000,000,000 humans (and their descendants) for 1000 years or so, you are going to need more than a few Enterprise style decks, cabins and cantinas, you are going to need a habitat.

Ideally your habitat will be completely sealed, every atom recycled. A small leak over the course of 1000 years is going to result in a lot of lost mass, and unless you have some exotic way of replacing mass this will translate directly into food shortages in the coming centuries.

This will likely lead to insurrection, rebellion and possibly war.

Energy cannot be replaced

In the vista between stars there's not much energy accessible, you can't refuel from solar energy and there's hardly any matter. The ship will radiate energy into space in the form of heat, and this energy cannot be replaced en route.

Unless you have some sort of magical limitless energy source (in which case why would you wish to leave Earth orbit at all), you have to carry everything with you, and minimise entropy.

Every matter to matter conversion is going to carry with it some inefficiency. Even composting potato peelings generates heat, which will ultimately be lost into space. An active little warm blooded mammal converts a lot of food into heat. Its faeces will be digested by bacteria producing still more heat, more lost energy.

Cold blooded sedentary animals

Assuming that you want to minimise energy lost as heat, I would suggest using a cold blooded sedentary animal. Perhaps a modified furry lizard, snake or tortoise. A snake can live for months on a single meal and will barely move during this time.


Cold water fish would also make reasonable pets.

Warm blooded animals would be a luxury

Warm blooded animals radiate heat and need to eat at least once a day. If you take a kitten with you, that kitten plus a millennia of descendants would possibly mean cutting the human payload. Warm blooded animals would be luxury pets, only for the rich.

There might even be social stigma attached to owing a dog for example, much as there is with SUV owners today. It's seen as environmentally and socially irresponsible.

Feral animals

As an aside, feral animals would represent a major threat to the mission. Unauthorised breeding (human and animal) would need to be curtailed.

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    $\begingroup$ I've known many children worth leaving behind for a kitten. $\endgroup$ – Oldcat Mar 11 '15 at 22:49

Tortoises might make interesting pets on a generation ship. They're relatively sedentary, and kids tend to like them, but they have one other interesting feature: they're extremely long-lived (the record is 188 years). Because they live longer than humans do, they would wind up being passed down from generation to generation, not unlike the ship itself. That could make them very useful tools for teaching children about the values that a generation ship's crew would need to hold to make the whole thing work.


Constructing a ship large enough to support a Billion people for a thousand year journey between the stars will consume more resources than it would take to fix the planet (no matter how badly damaged). Building on the ground (or even under it) would be easier than moving that many people to orbit, even if terrestrial archologies are scaled up to support many more billions of people. One would need to assume something along the lines of the death of the sun to justify abandoning the Earth. Additionally, once possessing the ability to create such ships, why would one need to resettle on another planet at all?

You might also want to consider a convoy of vessels rather than a single massive vessel - it would be less of an engineering challenge and not an issue of putting all your eggs in one basket.

Regardless, concerns about being religiously neutral are fairly irrelevant. A ship that large would be big enough that such a person would not even need to be aware of entire cultural populations in other parts of the ship. Taking intolerant religious people along at all is likely not a good idea - holy wars in such an exceedingly fragile and uniquely vulnerable environment are not a good idea. Any kind of religious strife should be strictly avoided - either everyone is of one religion and keen on executing apostates, or better to just not bring intolerant religious people in the first place.

The amount of waste the animals produce is completely irrelevant - with that large of a ship, you cannot just store your waste and eat pre-made supplies for a billion people for a thousand years. The entire food/waste system will be an ecological cycle - more animals in the mix just very slightly scales up the process, or maybe they are an integral part of your food supply and waste processing (certain human-inedible plants process waste, animals eat these plants, then humans eat the animals and/or plants grown in animal waste).

Once concern would be animal socialization. Unless you are thinking of your future domesticated animals being solitary creatures or completely bereft of intelligence (though I suppose they could just be factory farmed), they need to learn their behaviors from their parents and other animals. How to feed themselves, clean themselves, interact with other animals, etc. etc. For this reason, you should probably keep a number of these domesticated animals alive on your journey. This has the side benefit of being a petting zoo to entertain the kids and a way to maintain the tacit knowledge and skills of animal husbandry.

Variety is rather important - people are not identical in their preferences. I know people who like to raise tarantulas while other people hate them, some people love big dogs but some others hate them, etc. No one animal will be the perfect pet for every individual and I see no reason why you should only have just one pet type - allow people to have whatever pet they like. To each their own preferences. If one kid wants a flexible dog to play fetch with, he could have a bendy dog. If another kid wants a lap cat, give him a lap cat. If some girl likes reptiles, let her have a gecko. Giving her a hamster instead, because everyone gets a hamster, would only disappoint her.


Permanent Lamb / Goat

Why engineer? Pick something with historical value.

Also, good eating :D Plus all the other benefits; wool, leather, eats a lot of different stuff (goat), etc.

If you're going for something different (because, hey genetic engineering!), I'd go against something with one color. You want a lot of different colors to be inherent (so people can tell their stoflar from their neighbor's), as well as some other physical traits...

Big enough to pet, and fur that wants to be petted. Something substantial enough to feel when it's on your lap, but not so big it can knock you down, or run wild in the halls.

I'm on the fence about teeth and claws. Sometimes getting a little blood drawn is a learning experience, and a sensation.

  • $\begingroup$ Make sure the population is large enough to prevent inbreeding. $\endgroup$ – user3106 Mar 11 '15 at 10:24
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    $\begingroup$ Why does this matter? You've got genetic engineering. Also, it's only going to have to be stable for X many generations of shipboard life, depending on the length of your generation-ship trip. $\endgroup$ – user3082 Mar 11 '15 at 10:41
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    $\begingroup$ @user3082 things engineered to only be for X years later tend to be made to last 5 times longer. Society will evolve and not want to give up the pets as well. $\endgroup$ – ratchet freak Mar 11 '15 at 11:08
  • $\begingroup$ Hi, "user3082". Just FYI, you might want to ask to have your old accounts be merged into your new account, so that you can enjoy your 3k+ total rep, and don't have to keep suggesting edits to your own answers any more. $\endgroup$ – Ilmari Karonen Mar 11 '15 at 11:26

A couple options come to mind.

  • Birds. They are small, they eat little. Nothing stirs imagination more than thinking about being able to fly...though maybe thoughts of escape while stuck on a generation ship aren't a great idea. I do genuinely enjoy the sound of birds when I wake up though.

  • Ferrets (rodents in general). Little pranksters that could certainly lighten the mood. Again small and resource light. As I mentioned on @sydan's post though...rodents have a propensity for getting themselves into places they shouldn't be.

  • Monkeys (or small apes). These would be the most resource intensive but probably the most helpful to the population. They can be taught, they need to be raised, filling people's spare time on a generation ship with a billion people is going to be no small task and this would help.

If we are talking about a ship that is this ridiculously large I don't think you need to limit yourself to one animal type though, the resource issue also seems less relevant as the requirement for pets will be minuscule next to what is required for that many humans. Heck, why not just have zoo Noah's arc style.

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Going a bit outside the constraints of the question, I know, but what about...


They can fit every one of your criteria, as well or better than living creatures (genetically engineered or otherwise).

  • Consume minimal resources, produce essentially no waste.
  • Can be made cute (perpetually so, unlike puppies, kittens et al.), and won't ever be dangerous to kids, no matter how many times their tails are pulled (off).
  • Carry no religious or cultural baggage, and are unlikely to attract any (unlike genetically manipulating real animals!), unless you have a Luddite cult or something, and what are they doing on a spaceship?
  • Simple AI programming can produce surprising (and surprisingly entertaining) emergent behaviours. Like real animals, they don't have to have thoughts and emotions for humans to ascribe those things to them and emotionally bond with them.
  • $\begingroup$ I am not sure how well emergent behaviour and won't ever be dangerous go together. $\endgroup$ – Burki Mar 13 '15 at 14:40
  • $\begingroup$ @Burki: That's because sci-fi has taught us to think that way. ;) But I'm talking robo-pets that don't have the ability to bite, claw, crush, or hook into the ship's central computer and stage a robot uprising. $\endgroup$ – Tim Pederick Mar 15 '15 at 10:04

The Humble Hamster (Without genetic engineering)

Seriously, how fun would it be to have lots of little hamsters rolling around the generation ship in space age hamster balls? This would be even more awesome in a 0g environment! They could have specially designed 0g hamster balls and tunnel mazes to play in.

They're small and don't require a lot of food, the food they do require is easy to produce. They don't produce a lot of waste and they're great fun for kids.

Only issue is that you might lose them (hamsters are great at escaping) and you will need a significant population to keep them going as they only live for a few years.

But I think the super fun benefits out-weight the problems.

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    $\begingroup$ My only concern with small rodents would be they tend to get in small spaces and have a certain proclivity for eating wires... $\endgroup$ – James Mar 11 '15 at 14:10
  • $\begingroup$ Tribbles! They're real! $\endgroup$ – paul Mar 11 '15 at 14:29
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    $\begingroup$ @James - I'd be really surprised if they don't have a rodent problem already -- surely a few rats snuck aboard in the millions of launches it would have taken to get this billion person habitat into space. So maybe a cat would make for a good pet to help keep down the rat population. $\endgroup$ – Johnny Mar 11 '15 at 15:27

One thing I would like to point out is that we have spent decades domesticating dogs, cats, cows, and other such animals. So why would we want to give up all that progress? We have even trained dogs genetically to respond to humans the way we want. So why not engineer them down to a more appropriate size, a more relaxed demeanor, and possibly a more religiously neutral shape (though I do agree with the other person who said that you probably won't want people with those kind of volatility in such a tight space anyway). My point here is dogs have been conditioned to like with humans from the beginning, so why throw that all away?


I agree with the other answers that with a ship that large, you could probably bring along a variety of animals. But for a new perspective, I would suggest thinking about potential pest problems.

If you have that many people on a ship, you will likely have some pests - rats, mice, roaches, and so on. Why not bring along pets that will help keep down the pests? Cats that are good at catching rats and terrier dogs breed for this purpose would be ideal. You could genetically modify these species to be better at preforming their tasks.

Actually, I would consider broadening this answer to include other pets that double as working animals. Would you have a disabled population that could use seeing eye dogs and the like? What about dogs trained to sniff out explosives or gas leaks?


I don't believe "normal" earth animals would make good pets for this case. They simply use up space and resources that really should be used for other things.

However, since you have genetic manipulation, maybe these "pets" do vital functions for the management of the ship. This would make them less of a luxurious burden and more of a necessity for the existence of the ship.

They could be the following in addition to just being "pets":

  • Heat Generators
  • Recyclers (of just about everything: air, water, etc)
  • Sources of Food (themselves, or, for example, maybe they create fruit or something)
  • natural environment "cleaners" or ship "repairers"
  • (most extravagant) Upon release from the ship, they are able to generate energy using radioactive space noise (or gather something else from "empty" space) and then they bring back some usable form of that to the ship.
  • $\begingroup$ The function of many pets before our high tech world was just that - pets ate scraps, kept down vermin, and provided food sometimes. Chickens, cats, dogs. $\endgroup$ – Oldcat Mar 12 '15 at 18:14
  • $\begingroup$ @Oldcat I agree, and I'm not sure whether you are in support of my answer or against it. Situations are different on a multi-generation ship, cats are not needed to hunt down vermin (there shouldn't be any), and dogs are not needed for hunting, tracking, or safety. The "pets" used for food generally aren't regarded as "pets" but as livestock, and I'm not sure how "keeping people happy" works when you send in your pet for processing. I suggest food more as, the pet creates a by-product which can be used as food (using resources that would otherwise not be used, coming from outside the ship) $\endgroup$ – DoubleDouble Mar 12 '15 at 18:39
  • $\begingroup$ Just ask those that raise chickens and pigs and then process them. $\endgroup$ – Oldcat Mar 12 '15 at 20:46
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    $\begingroup$ @Oldcat My family raises chickens.. For myself there is neither happiness in caring for them nor sadness when you process them - its just the way it is. This is why I call them livestock rather than pets - you don't get attached. $\endgroup$ – DoubleDouble Mar 12 '15 at 21:01

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