Let's say I have been chosen to evaluate whether or not alien worlds contain sapient life before we terraform them. Just assume that we learned to work together and live as a species in peace, treating intelligent life equally (though in reality we never will).

Obviously this is a hard job and since I don't want to be fired, I can't make a mistake. This becomes even harder when I look at all the possibilities of stone age intelligence. Tool use is not a trait that is exclusive to sapient animals, after all. If the species was a sapient plant, I couldn't use earthly evolutionary rules. If they had multiple bodies, I couldn't rely on the rules of monobodied aliens.

And these are just aliens that can be explained. For more extreme cases, it becomes impossibly difficult to tell. How can I, to within reasonable doubt, determine whether or not an alien species at a stone age level of evolution is sapient?

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    $\begingroup$ How do you define "sapience" for your question? All oor nothing or is it a gradual thing? Do "sapience" and "sentience" differ? $\endgroup$
    – o.m.
    Commented Jul 15, 2016 at 5:39
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    $\begingroup$ @o.m. Yes, almost every animal is sentient. From the smallest ant to the wisest man. Until further research is done, only humans are sapient $\endgroup$
    – TrEs-2b
    Commented Jul 15, 2016 at 5:59
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    $\begingroup$ I'm not sure if an individual ant meets the definition of sentience. They are pretty much driven by pheromone triggers. $\endgroup$
    – o.m.
    Commented Jul 15, 2016 at 6:03
  • $\begingroup$ Hi TrEs-2b. I edited the question to try to fix a few issues I saw with it. If you feel I changed your intent, by all means feel free to roll back the edit. I would still encourage you to, as o.m. suggested, provide a clearer definition of "sapience". What is the actual criteria? $\endgroup$
    – user
    Commented Jul 15, 2016 at 7:45
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    $\begingroup$ When in doubt, pull out. Seriously, if there is life on the planet before you then terraforming it would most likely annihilate that life. It could evolve to sapience or not, but people freak out when an earth species is close to extinct, much less causing the extinction of millions of undiscovered species. $\endgroup$ Commented Aug 3, 2016 at 14:29

4 Answers 4


Start with tool use. It may be that non-sapient animals use tools (however, the 'sapience' of tool using species may be reevaluated as our understanding changes). It may be you have sapient beings that do not, for whatever reason, use tools. However, it should be a relatively visible criteria to start you off - and I would suspect very strongly that you'll need more than one criteria anyway.

Any tool-using species should then be put on a "maybe" list for further evaluation (and I second a4android, tool using plants get a "yes" from me) - and depending on relative abundance of terraformable planets, maybe that planet or at least the relevant habitat should be avoided anyway - because even if they are not sapient, they might still become so, at some point. When it comes to ethics, a few false positives (protecting a non-sapient species) is far preferable to even one false negative (that would be effectively genocide of a sapient race)... and it's a lot easier to go back and terraform later, than to undo the process if you were wrong.

Maybe the next criteria would be alteration of the environment - obviously the more 'unnatural' the alteration, the easier to find and evaluate. Maybe something like bird's nests doesn't qualify, but maybe the more elaborate construction of termite mounds will make them worth a second look. Beaver dams fall somewhere between. Or moving from benefiting from fires to using embers from one area to start new fires (unsubstantiated, but the idea is there) in a different one. Actually, I'd put any fire-using species on the 'maybe' list anyway, its a pretty dangerous thing to use.

A third criteria you might want to look at it communication - if there are analyzable long-distance signals, that again becomes a reason to go on the 'maybe' list. If they're unusual to the planet's wildlife, or 'unnatural', that might be worth some extra consideration - for example, if the animals use sound and scent, then drawn pictures might be worth a second look (or radio waves, but you said stone age). Also, most animals will want to communicate at a relatively short range, since they're concerned with their immediate surroundings, so something broadcast over half the continent away is worth looking into (relay towers, beacon fires?). Any obvious signs of organization - especially large scale organization, or coordination and cooperation between separate groups, should draw your attention for a second look.

And on that note, cooperation between species should also be worth a second look - it can signal compassion (protecting vulnerability even in other species) , or domestication (putting other species to work). You might get some false positives from animals who developed symbiosis, but probably the more similar the species are, or the more the relationship costs either, the more I would think it likely to be the action of sapient beings. If the species is after similar resources (like both hunters) cooperation is more difficult than if the species are specialized and non-competing; likewise if a species is taking actions that benefit the other but cost the first in time or energy (driving off predators, caring for injured), it seems more likely to be reasoned than pure instinct, as opposed to actions that simply happen to benefit both (feeding off of parasites).

So now you have a few criteria for a shortlist, how to evaluate further? Go in person, and study a lot more closely. Check to see how these species react or adapt to something new, if you can find any kind of mutual communication, how these species will react to an alien presence (er, that's you). Take environmental factors into consideration, as much as you can - how much their behavior is different from other similar species on that planet, how much is taught as opposed to instinctive, or how much might be reasoned and how much reactive, and so on. As a bonus, you might make a final communications check by visiting the planet directly, and wandering about for a bit - the better to see if anyone tries to communicate with you.

Then you've got your planets all lined up - some with nothing concerning, some that are still 'maybes' - with a probably sliding scale of maybe-just-animals to likely-to-be-sapient, and some where you will definitely want to say leave it be and find a new planet. Depending on how many planets are capable of being terraformable, and how much stock your culture puts into preserving diversity and preventing extinctions of even animals, your organization might be happy crossing off all the 'maybe' planets, or might only protect the really truly likely ones.

  • $\begingroup$ other useful criteria, do they have a concept of death, do they make tools that are only useful to make other tools, do they show empathy, do they make art, the last may be hominid exclusive on earth. $\endgroup$
    – John
    Commented Dec 3, 2022 at 5:10

Firstly if a plant had paleaolithic tools and it was making and using them you can be fairly sure it is sapient. Animals do have a capacity for tool use and relatively limited ability in tool making, but plants don't use tools full stop.

Secondly the real problem is how sapience is understood. Currently there is a reevaluation of constitutes intelligence. This means it all to likely that by the time we get around to evaluate the sapient quotient of plants and hive organisms the parameters for determining sapience will have changed considerably. Many Earth-evolved species may be deemed sapient. This includes various birds like parrots and crows. Even dogs, dolphins and other cetaceans.

One thing about sapience is the environment is a major determinant in shaping the evolution of intelligence. For example, parrots from the Vanuatu live in an environment with rich complexity and is relatively free from predators. This enables them to develop a remarkable degree of tool making and use. Take into the various environmental factors present to provide supporting evidence for your evaluation.

Industrial relations and personnel management should have improved in the future and especially so for interstellar expeditioners. So if you make a mistake you won't need to worry about losing your job. You get counselled on doing a better job in sapience evaluation, but that isn't a great hardship, is it?


You could observe them and determine how much forward planning they are doing, then (hopefully) make some judgement on whether the forward planning required being able to cope with abstract concepts.

For instance, squirrels do forward planning by burying nuts for the winter. But there is not much abstract thought there. Just "I need food for later". (Possibly no thought at all, since the squirrels who don't bury nuts all starve to death and don't pass on their genes).

Stone Age guy also needs food to survive the winter, and also likes eating nuts. However, what he does is make a lot of stone spearheads. Then he goes to his neighbour's cave and swaps them for a tiger skin. Then takes that tiger skin to the village down the road and swaps it for an enormous pile of nuts and some help to carry them back to his own cave. His forward planning is much more complex than the squirrel's. And it involves a more abstract concept: trade and payment.

If the stone age aliens are using any object with zero survival value as an 'institutionalized favour' or IOU, then they've invented currency, and have a very sophisticated level of culture that goes way beyond the animal. A caveman giving another a stone tool for a tiger skin is not currency. A caveman giving another a piece of clay with some marks on it that mean "I owe you a stone tool" is. (I promise to give the bearer on demand...)

Meanwhile... art. If there is anything resembling art which isn't directly associated with getting laid (so more than a bower bird's decorated bower), then there's that abstract thought again. If the aliens are putting a lot of effort into making paint pigments, processing clay to make sculptures, tattooing each other, etc and it has no survival value, then they are again beyond mere animal intelligence.

Of course, being alien, their art may be difficult to recognise. You may think they are scent marking their territory. They make think that they are arranging their poo in alphabetical order by colour to please the forest spirits. :-)


One of the main tenets of the Science of Discworld books is that the storage and transmission of knowledge has been key to the advancement of the human race.

Making sure that accumulated knowledge is not lost upon the death of an individual is vital to progress. This is very similar to how a positive mutation in Darwinist evolution must become spread throughout the population; as long as it remains restricted to a few individuals it could easily be lost.

For another example, look into how the loss of Fermat's last theorem has caused hundreds if not thousands of scientists to try and recreate what was lost.

So there is some ground to state that an individual might be sentient, but only a species may be said to be sapient, namely when they are commonly exchanging knowledge amongst individuals and are using this strategy to gain more knowledge.

Tool use alone would not be enough. You would need to see tool use being tought to subsequent generations and those generations would need to build upon the knowledge they received to develop new uses for existing tools or new tools.

  • $\begingroup$ Good answer, but a fairly low bar. Many animals pass knowledge to subsequent generations. AFAIK it is pretty much certain in any species that are social, where grandparents are involved with nurturing infants and helping adolescents. Men brought ring-necked parakeets from the tropics to the UK. They escaped and have learned to thrive here. $\endgroup$
    – nigel222
    Commented Jul 15, 2016 at 15:29
  • $\begingroup$ @nigel222 Well I wouldn't put the bar that low. I think you can draw a clear enough line between passing down survival skills, and passing down actual knowledge. $\endgroup$
    – Falc
    Commented Jul 16, 2016 at 8:12
  • $\begingroup$ (continued since I'm still new at commenting...) The Science of Discworld goes into some more detail about how we spread knowledge through stories, through cautionary tales and shining examples which have no immediate bearing on the immediate situation at hand but which could save your life some time down the line. I know of no other animal who has the communication skills to do that... $\endgroup$
    – Falc
    Commented Jul 16, 2016 at 8:22

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