I was wondering if intelligent life, in the sense that the species' greatest evolutionary advantage is its' intelligence, is an evolutionary inevitability, or was it a completely random occurrence for us? Or was it somewhere in the middle where the conditions were just right for the various species of humans to emerge?

EDIT: removed the hard-science tag. I know there might not be concrete scientific answers, but I was more interested in what people's thoughts on the matter were. For instance, for the more hard-science fiction writers, how do you justify intelligent species that are not humans?


closed as off-topic by Mathaddict, Renan, Arkenstein XII, Jared K, M i ech Jun 3 at 21:33

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This question does not appear to be about worldbuilding, within the scope defined in the help center." – Mathaddict, Renan, Arkenstein XII, Jared K, M i ech
If this question can be reworded to fit the rules in the help center, please edit the question.

  • 3
    $\begingroup$ I do not see exactly how this question is connected to worldbuilding. In it's current phrasing its will be more fitting somewhere at biology.stackexchange.com $\endgroup$ – Cumehtar Jun 3 at 17:48
  • 1
    $\begingroup$ While this is a great question, the 'hard-science' tag makes it nearly impossible to produce a valid answer, when we ( so far) have only one instance of intelligence in the known universe. $\endgroup$ – Joe Jun 3 at 17:57
  • $\begingroup$ @Joe Sorry I was under the impression that the hard-science tag merely meant that I didn't want fantasy explanations to the question. Does it exclude hypothetical science thought experiments too? $\endgroup$ – SeekingASensei Jun 3 at 18:00
  • 2
    $\begingroup$ Considering how many people have devoted how many years researching this and we've not had any results... We as a species, have spent literal millenia on the subject. And we're not even close to figuring it out. So it seems like the question is too broad. $\endgroup$ – VLAZ Jun 3 at 18:01
  • 1
    $\begingroup$ It is pretty obvious that "intelligence" in the sense of human intelligence is not an evolutionary inevitability; there are millions and millions of living species on Earth, of which only one is intelligent like humans, and a dozen others exhibiting something a little bit similar (other great apes, dogs, some cetaceans, corvids, maybe some cephalopods) -- and even this somewhat similar intelligence is severely limited. So we absolutely know, from practical practice, that 99.999% of the living species are not intelligent in the human sense. $\endgroup$ – AlexP Jun 3 at 18:53

Short Answer: we don't know, but we have a few ideas.

we know a a few things that could encourage it and a few things that might discourage it but those a a few points on a giant see of possibilities. in all likelihood it was the interaction of many positive forces that caused human like intelligence to evolve. We just don't have a good idea of why intelligence evolves. We do know however it is a progressive process you you will not get intelligence fungi, you are going to work your way up, all of the highly intelligent animals evolved in groups where intelligence is already widespread, (primates, cephalopods, elephants, cetaceans, parrots)

What factors can encourage intelligence.

  1. Sexual selection, in general anything can be encouraged by sexual selection, if mates find X attractive X will tend to increase in the population. Sexual selection likely plays a role in all intelligences.

  2. omnivory encourages intelligence and a good memory, for animals omnivores tend to be more intelligent, they have to keep track of more factors, and encourages manipulation of food since you can't evolve a system that handles all foods equally well. But this is also a fairly weak effect.

  3. social, social organisms tend towards intelligence, you have to keep track of more factors including what others are thinking and who is not acting social. This also leads to communication which also encourages intelligence. It is also competitive, you are competing with other intelligent creatures so you can have self reinforcing selection. Being social is probably the strongest cause, no animal with high intelligence is solitary.

  4. The ability to use tools, normally we think of using tools as stemming from intelligence, but an organisms that cannot use tools will have a harder time generating intelligence.

  5. K strategist, having big high care offspring encourages teaching which in turn encourages intelligence.

Note: we don't know if you need all of these, again we don't know all the factors that drove humans to our level intelligence.

What factors discourage intelligence.

  1. Well to start anything that eliminates the above options, so a solitary, r strategist, primary producer is likely never going to evolve intelligence. Likewise a creature that does not mate at all is also unlikely to evolve intelligence.

  2. Poor environmental productivity, intelligence is expensive so it is unlikely to evolve where every calorie is at a premium so likely no desert, tundra, or cave living intelligences.

  • 1
    $\begingroup$ Mostly I agree with this, but it could be argued that poor environmental productivity is more conducive to intelligence. Being able to adapt to unforeseen environmental deficits is huge. An animal that instinctively goes about acquiring the same food from the same sources every time needs less intelligent than the animal that needs to figure out how to kill oversized prey with sticks and stones or starve. $\endgroup$ – Nosajimiki Jun 3 at 21:43
  • 1
    $\begingroup$ @Nosajimiki Note the examples I gave are places with almost no food, intelligence is not a big help in such places (without technology)it is not that it is hard to get it is there is almost nothing too get, intelligence is too costly to evolve in conditions where you cannot space 1/3rd more calories. $\endgroup$ – John Jun 4 at 10:21

Generally speaking, intelligence will increase over time if there's a reproductive advantage to being smarter.

This is clearly not always the case; we've still got a myriad of species with tiny brains (there's a planarian with a number of brain cells in the mere thousands, fully mapped by function and all identical, yet it survives, reproduces, and can even be trained).

However, in some environments and conditions, a creature with more brain power has an advantage that makes it more likely to produce larger numbers of offspring. In the case of humans, this may have been a drought that lasted half a million years in eastern Africa, or it might have been a nearby supernova that killed off a large area of forest, or it might have been the presence of hominid-specific carnivores -- all of this is history running back as far as several million years, so there'll never be real certainty.

And that's the problem -- there is no certainty about anything in evolution, because we can only see the end result of a process that mostly took place in what, compared to a human lifespan, is the deep past. All we can say with certainty is that conditions that reproductively favor intelligence will tend, over evolutionary time, to foster intelligence.


Define "intelligence." No really. I mean it. What is it defined as?

The question of what causes intelligent life to evolve is somewhat stymed by the reality that we have trouble even defining what intelligence means. So that's the real problem here... and an interesting one it is.

If I dig at what is similar among the varied attempts at definitions, I find a common thread: discrete pattern matching. We see it in IQ tests, for example. The ability to identify something in discrete abstract terms, manipulate it in your head, and then draw conclusions seems to be a reasonable basis for exploring intelligence itself.

If I draw from this and my own experience, I find the most critical aspect towards the development of intelligence is the presence of things which do not change over time on their own, but which can be changed by an individual. For example, rocks tend to not move on their own, but a human can pile them up into a cairn. Once piled, they tend not to move (until they eventually tumble down).

The connection between that and intelligence is that I was able to describe these things in language. You can take those words, and manipulate the ideas as you like. If you don't like them, you can knock them down.

There seems to be a symmetry between these environments that have these traits and words within our own languages. I think there's a strong correlation to be argued there.

Some animals seem to have something close. I watch my cat knock a glass off the table. I want to scream at him for intentionally being a pest, but when I look at it, he's as curious about it as anything. He seems generally unsure as to how it will go, even though the little furball has done it a dozen times before. Contrast that with my daughter, who knows full well what happens when the glass gets knocked off the table. There's something different between them, and I would argue that thing is intelligence.

So when it comes to evolution, I would note that while intelligence evolved on Earth, it also didn't evolve millions of times. It isn't clear that it's just the way evolution had to happen. It's much more complicated than that. However, having a species discover ways to intentionally move objects that otherwise don't move on their own, and select for that, is probably a good start.

  • 2
    $\begingroup$ I dunno, I'm pretty sure my cat knows that if he pushes the glass it will fall. He just finds a certain satisfaction in it. $\endgroup$ – Nosajimiki Jun 3 at 21:48

Intelligence is useful in a fairly narrow range of environmental complexities and rates of change.

Consider the following:

If your environment is sufficiently predictable that you can come up with a single best-case strategy that always works (or works with a consistently high-enough probability) all the time, then you don't need intelligence. Evolution can just hard-code the correct instinctive behavior to ensure your survival.

However, if your environment is completely random, or so complex that predicting it is computationally infeasible for wetware, then you might as well just act randomly (neither intelligent thought or instinctual programming will do any better), and again intelligence is not required.

For intelligence to be evolutionarily advantageous, you need an environment that changes fast enough that evolution can't keep up with reprogramming your population's instinct, but changes slowly enough an exhibits enough consistency that allowing an individual to learn over its lifetime and expend energy on reasoning out solutions to novel problems actually confers a significant advantage.

The easiest way to accomplish this is to take advantage of the other lifeforms in the environment--particularly those of one's own species. This is why most of the most intelligent animals are highly social animals--including us. They use their intelligence largely for navigating constantly-changing social dynamics, and then are incidentally able to apply it to other things. However, that does not mean that intelligent creatures must necessarily be social; octopuses are largely solitary and yet still famous for their brains, which they need in order to operate in a highly complex oceanic environment that changes relatively rapidly over time (though still largely in terms of the other living organisms they must interact with). If a social octopus were to ever evolve, though, I'd bet you'd see a fairly rapid explosion in their already-respectable intelligence as a result.

Our own evolution shows evidence of both factors at play--hominids have been highly social creatures for longer than they've been hominids, the most recent ancestors of humans appeared during periods of climatological and ecological change (so that individual intelligence helped pick up the slack that slowly-changing instincts and physical features couldn't handle), and the migration of our species into a wide range of different environments created a feedback loop where intelligence allowed us to deal with changes to our environment as we migrated, and migrating to new environments forced us to be more intelligent to deal with the changes they brought.

So, putting it all together, it seems that you are most likely to see human-level intelligence arise in species that are highly social, spread across many environments, originate in a highly complex or changing ecosystem, and are generalist predators or omnivores (i.e., have an ability and need to deal with a wide range of other organisms), although dropping one or two of those features may still allow intelligence to arise anyway if the remaining pressures are individually strong enough.


Stable environment

While intelligence undoubtedly existed independently of climate, I propose humans were really able to start using it to their advantage only after this happened:


This shows temperature graph for past 50 thousand years, it can be seen the climate was exceptionally stable for most recent 10000 years. Which neatly coincides with invention of agriculture and rise of first ancient civilizations.



As already said in the other comments, there is no way to know it for sure. We know of only one specie that could reach a superior intelligence, so everything else is, at best, an educated guess. And consider also that because of the very limited number of real life examples, even the concept itself of intelligence is still debatable...

Some thoughts:

  • Very roughly speaking, our brain can switch between two main working modes: a low energy, "react to external stimuli" and a very costly "thinking" mode (where we can filter out external stimuli and run "simulations" of reality inside our minds); while all animals have the former mode, the latter is peculiar only of humans (about the subject, there is of course some debate also about some behaviors of dolphins and big apes)
  • Intelligence is costly, because brain requires a lot of calories to work in "thinking" mode: apes started to develop bigger brains because of the availability of easy-to-collect high-calories food (fruits), so the background has a strong influence
  • The tricky part: according to some theories about evolutions, human evolution was triggered by a big climate change, when African forests became prairies: some apes had to adapt to the new life in the grass (far harder and more dangerous than in the woods), becoming bipedal walkers. So, maybe a difficult situation generates evolutive pressure to develop intelligence
  • At the moment, almost all animal species are in a very difficult situation because of the rise of a single intelligent species... Will they develop intelligence in response? I think that the speed of changes matters: an environmental change happens in the span of tens thousands years, leaving enough time to adapt. But the rise of mankind happened in the span of few thousand years (and accelerated only in the last few centuries). Life always finds a way, of course, but I don't think there is enough room to develop sophisticated responses to the human-created selective pressure
  • About the point above: I think that on a single planet there is only one ecological niche for an intelligent species, because the time between the rise of intelligence and the "conquer" of the planet is so fast to disrupt all alternatives: small animals don't have enough "brain" size, while big animals are the first to have their population reduced to a level that doesn't allow for sophisticated evolution.

Basically, my rough recipe for intelligence evolution: a pre-existing "almost" intelligent species, that finds itself in a situation of strong evolutive pressure (reduced food, more dangers), and no other intelligent species.


Not the answer you're looking for? Browse other questions tagged or ask your own question.