Think about a scenario in which, on a given planet, a complex life form has already evolved.

In your opinion, what are the odds, for this complex form, to evolve towards intelligence?

  • With the terms "complex life form", I'm referring to something comparable to an Earth's complex mammal.

  • With "intelligence" I intend a life form capable of ask itself a question like the one I'm submitting right now.

Another way of basically rephrasing the same question is: "is there a certain level of complexity after which the evolution of life form MUST naturally tend towards intelligence, or is intelligence just an accident in the evolution of life?

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    $\begingroup$ This is similar to asking "will a sufficiently advanced computer become intelligent". The answer very much depends on the definition of "intelligence", and then leads into a lot of unknowns. The definition you propose tends towards "consciousness", which we don't really understand the causes of. So I would say, "ask a philosopher"... $\endgroup$ – IMSoP Oct 14 '16 at 14:28
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    $\begingroup$ Looking at the general state of the world today, I'm not seeing much evidence of intelligence. $\endgroup$ – Innovine Oct 14 '16 at 14:33
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    $\begingroup$ Nope. Higher Intelligence was there at the start of the universe. It has been devolving since then, $\endgroup$ – Manoj Kumar Oct 14 '16 at 18:44
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    $\begingroup$ I'd say that the odds of any specific life-form to develop in such a way is effectively zero. But the odds for some life-form in a complex ecosystem to develop in that way is at least slightly more than zero. In a half-billion years here, just one form out of all that ever evolved here managed to do it. You might figure the odds as a ratio of 1 to the total number of complex forms ever on earth, as a starting point. We possibly made it only because of no recent ELE. $\endgroup$ – user2338816 Oct 15 '16 at 11:15

No, this is definitely not the case. Increased mental power has a significant calorie and other cost so it needs to give equally significant gains for it to be favored by evolution. In other words "good enough" is fine. In particular, local maxima where you are well suited to your environment are easy to reach and then hard to leave. It might be possible to become more fit - but only by becoming less fit first. That is unlikely to happen so you are probably going to just stay where you are.

For example mammals will find it very hard to evolve longer necks (the giraffe is at the limit): https://svpow.com/2012/09/30/mammals-have-short-necks-because-of-local-maxima/

Remember that evolution has no goal or objective, no long term plan. Each individual change needs to either have a benefit (or at least no cost) or over the long term it will not succeed.

The dinosaurs ruled the Earth for millions of years, far longer than our mayfly species has even existed, and in all that time they did not evolve intelligence of the sort you are describing.

For intelligence you need just the right combinations of factors to come together in just the right sequence so that each step makes sense at that time until in the end sentience emerges. A lot of people think that our intelligence actually came out of the fact we were living together in social groups. We developed bigger brains to defeat each other, and then that incidentally let us defeat everything else.

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    $\begingroup$ Conceivably they developed intelligence but not tool-making. T-Rex may have had an intricate aesthetic concerning the poetry of the hunt, complete with traditional sagas and competing schools of style, but no interest in using their stubby little hands to try to build things. $\endgroup$ – WhatRoughBeast Oct 14 '16 at 14:36
  • $\begingroup$ Even excluding dinosaurs, we've had 65 million years since their extinction, and tool-using (beyond crude sticks and stones) for perhaps 65 thousand years. $\endgroup$ – jamesqf Oct 14 '16 at 16:56
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    $\begingroup$ To quote an unnamed university professor "Evolution isn't survival of the fittest, it's survival of the good enough." $\endgroup$ – PipperChip Oct 14 '16 at 23:50
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    $\begingroup$ @WhatRoughBeast - so, T-rex died out because Shakespeare and Pushkin were replaced by modern poets with no rhyme or reason? $\endgroup$ – user4239 Oct 15 '16 at 15:16

In addition to what Tim B said about evolution favoring the fittest organism, which may not necessarily be the most intelligent, it sounds like what you're asking for is sentience, rather than raw intelligence per se.

Slime molds, for example, are capable of surprisingly intelligent pathfinding, but are very, very far from any kind of sentience, self-awareness, or other qualities which we traditionally associate with human intelligence. Similarly, the computer you're using is certainly extremely intelligent in its number-crunching ability and with the right program can solve incredibly complex tasks, but clearly lacks sentience.

So the simple answer is that no, it does not appear that evolution intrinsically favors intelligence. Intelligence is a trait with trade-offs that are not always worth it. However, the more complex answer is that even if intelligence exists, it may not be intelligence as we know it. An organism could be a highly intelligent, competitive problem-solver, but utterly lack the forms of cognition like self-awareness and introspection that are implied by your question.

If you're interested in a (fictional) example, the core theme of Peter Watts novel Blindsight is whether or not sentience is a prerequisite for intelligence, and might give you inspiration for your worldbuilding. It's worth a read.

  • $\begingroup$ There is a problem with self-awareness: nobody can tell whether any other entity has it. You can only tell that you are self-aware and the we assume other humans are too, but that's only by Occam's razor—everybody else pretending self-awareness so you don't think you are the only one would be more complicated. But we can't tell whether animals are also self-aware and whether self-awareness is a binary thing that appeared at some point or a continuity that grows from simpler organisms to more complex ones etc. $\endgroup$ – Jan Hudec Oct 16 '16 at 9:55

It is not intelligence that's the problem - it's how your social system interacts with that intelligence to create (or not) civilisation. There are a whole bunch of intelligent animals on Earth, which can pass the Mirror Test:

  • Humans
  • The various extinct humans, such as the Neanderthals
  • Common chimpanzee
  • Bonobo (pygmy chimp)
  • Various types of parrots
  • Various types of corvid (crows, jays, magpies, etc)
  • Elephants

So from this we can deduce that raw intelligence is quite common. Thus you would expect it to evolve on an alien planet.

However, for an intelligent creature to develop the sort of civilisation needed to type away at our keyboards and ask/answer questions on WBSE, there are a whole bunch of biological things which are required:

The animal CANNOT be territorial. That's 'terriorial' in the biological sense - having a defended home range. A territorial animal will fight tooth and nail to stay in its territory and to keep others out. It will never leave its territory unless driven out of it by a rival.

Humans are not territorial - if we were, there would be no such thing as moving house, foreign holidays, football teams playing away matches, commuters going to the town down the road to work, postmen delivering the mail, etc. (Humans can be possessive about land, but it is not as intense or instinctive as biological territoriality).

Territorial animals view both their neighbours and strangers as the enemy. They think they are out to kill them and to take their stuff. So territorial animals can never invent trade. Which means that they can never invent an enormous list of technologies which require raw materials to be gathered from all over the place, or which require cooperation of widely scattered groups of people.

For instance, me typing this requires some folk to have drilled in the North Sea for natural gas, some other people to have piped it to a power station, folk to run the power station, maintain the national grid, etc etc. And that's before we even begin to think about what the computer is made of...

If I could wave a magic wand and instantly give proper opposable thumbs and a human level intelligence to the chimp, the bonobo and the African bush elephant, not all of them could create a civilisation like a human one.

  • The bonobo possibly could. They have territories, but border encounters seem to often be non-aggressive.
  • The chimp couldn't. Male chimps are just too psychotically aggressive to strangers.
  • The African bush elephant could. They are not territorial and can have friendly as well as neutral or aggressive interactions when herds meet.

So something distantly related (elephant) to us is more likely than the chimp to recreate civilisation.

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    $\begingroup$ Don't forget about dolphins in the list of mirror test passing mammals. They would provide another unique example of intelligence in a non-terrestrial environment. $\endgroup$ – D.Spetz Oct 14 '16 at 17:29
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    $\begingroup$ The mirror test is hardly an exclusive test of intelligence, though. It also tests for vision being the dominant sense: a blind genius would fail the mirror test, while few humans would recognize themselves from their smell, or the sound of their own voice. $\endgroup$ – jamesqf Oct 14 '16 at 21:25
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    $\begingroup$ @Davor: But if you have a whole species that has genius-level intelligence, but no visual sense (or a visual sense that is subordinate to other senses), the whole species will fail a mirror test. Or consider dogs: like many mammals, their vision is subordinate to smell & hearing, yet most psychologists insist on a visual mirror test rather than developing an olfactory one. (FWIW, my neighbor has a blind dog. You'd never know it from watching him, though.) Imagine smell-oriented aliens applying an olfactory intelligence/self awareness test to humans :-) $\endgroup$ – jamesqf Oct 16 '16 at 23:05
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    $\begingroup$ @Daerdemandt: Humans, like many other species, are territorial as groups, not as individuals. For map examples, the Balkans, Israel/Palestine, India/Pakistan come immediately to mind. Not to mention that humans can extend their concept of territory into mental spaces, so it becomes admirable to kill people of different cultures or religions, if you can't subjugate/enslave them. $\endgroup$ – jamesqf Oct 16 '16 at 23:09
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    $\begingroup$ @jamesqf I specifically stated BIOLOGICAL territoriality. Humans are not territorial in the biological sense - they are possessive. Sometimes they get possessive about land, but it is not the same. Biological territories do not need maps or "keep out" signs - every member of the species instinctively recognises the border markers. Territories are only big enough to feed you and your offspring. You never leave your territory. All sorts of human things, like inviting your neighbours round for a beer, or sitting next to a stranger in the cinema are impossible for biological territoriality. $\endgroup$ – DrBob Oct 17 '16 at 16:45

No one has the faintest idea. It's obviously possible (or we wouldn't be here), but one sample does not give much more information than that, particularly in a possible sample space as large as the universe. And, of course, Fermi's Paradox ("If the development of intelligent life is statistically inevitable, where is everbody?") suggests that the odds may be bad for reasons of which we are unaware.

As to the second version of your question, ALL evolutionary changes are accidents (barring the existence of an Intelligent Designer), so it's clear that there is no imperative driving a species towards intelligence. If it's clear that early stages of the pathways which produce intelligence are also strongly advantageous to a species' survival, then there will be strong evolutionary pressure (at a species level) to encourage (preserve) such developments, but there is a catch. If the early stages are strongly positive, later stages of development must also be positive with respect to these early stages, and the early stages might arguably lead to intense specialization in the species' ecological niche, which would tend to inhibit further development. So, for instance, if a species of anteaters becomes a fabulously successful hunter of ants due to its intelligence, as long as this lifestyle is adequate there will be little incentive to preserve developments in intelligence which do not aid in hunting ants. This suggests that "intelligence" as we define it will be most likely to arise in generalists/omnivores rather than specialists. It also suggests that intelligence is more likely to arise in prey species rather than top predators. Once we developed tools and weapons we became apex predators, but before that it seems to have been a different story,

  • $\begingroup$ One possible answer to the fermi paradox is: $\endgroup$ – Trip Tucker Oct 14 '16 at 14:52
  • $\begingroup$ Is not a matter of where but a matter of when since the lifespan of intelligence is very very short compared to the time needed by evolution to reach intelligence $\endgroup$ – Trip Tucker Oct 14 '16 at 14:54
  • $\begingroup$ Oh yes. As Arthur C. Clarke once stated, "In the long run, intelligence has not been shown to be survival trait". Also see Bruce Sterling's "Swarm". $\endgroup$ – WhatRoughBeast Oct 14 '16 at 14:59
  • $\begingroup$ Simple answer to Fermi's Paradox: Intelligence eventually develops technology, technology discovers fossil fuels, global warming renders intelligent life extinct. On current evidence, there's maybe a few centuries where that intelligent life could have radio &c that could be detected on other planets. $\endgroup$ – jamesqf Oct 14 '16 at 17:00
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    $\begingroup$ @jamesqf - And, as always, xkcd has something interesting to say. xkcd.com/962 "It's not that life inevitably destroys itself with war. It's just that it takes longer to develop space colonization than it does to invent an activity more fun than survival." $\endgroup$ – WhatRoughBeast Oct 15 '16 at 2:22

This is definitely an unknown in current scientific theory. No one knows how "natural" the evolution of intelligence is. Fortunately, you did not tag this question with hard-science, so we can make guesses!

We would need to define "intelligence" to answer the question. You saw this, and provided your definition: "...a life form capable of ask itself a question like the one I'm submitting right now." Excellent! Now, in proper form, I will suggest a counter definition which is hopefully inline with what you are thinking, but is easier to answer in biological terms. To do so, I would like to call upon an lyric from an old Jethro Tull song, Thick as a Brick:

The doer and the thinker, no allowance for the other.

This line always caught my attention. Those who do and those who think are put at odds. However, it does suggest a key attribute of "thinking" that I believe gets close to answering your question: it doesn't "do" anything.

Consider this as a model for thinking: the goal of thinking is to explore the time evolution of something (typically a model of the world around us), while isolating it from the rest of the world as much as possible while it is in motion. Once it ceases moving, we explore the results, and decide if we want to act on them.

A classic example of this would appear in combat. If you think about throwing a punch, you "throw it in your mind," and think about what will happen. Only once your mental punch lands, and you assess the idea, will you throw the punch. If it assesses poorly, you want it to have no effect on the world. Maybe you'll think up another punch to try. Or maybe a kick. The key is that when you decide what to do, finally, you haven't done anything. This means your punch is going to be very slow. To compensate, while we are thinking, we tend to do something we think is safe to prepare for the possibility of action. In combat, that's called telegraphing, and it tends to give your opponent an advantage.

So we see two major aspects here. First is what we just discussed, that intelligent thoughts are rather isolated from the world while they are in motion. The second is that we let them evolve in our heads, which takes time. The answer we get from an intelligent question is one which was valid several seconds ago. I think this is a key factor for the evolution of thought -- it will only occur if answering a question that's a few seconds old is still useful a few seconds later.

So this is where I believe evolution is natural. Evolution is natural in cases where there's value in capturing the "state" of something in the world, and playing with several futures in isolation before deciding how to act. For this to be natural, there have to be decisions to be made where the world isn't changing so fast that the decision is useless after the fact.

I think the manipulation of inanimate objects is the reason intelligence is natural. If the manipulation of inanimate objects to help you out is valuable, whether its using tools or building shelter, there will be value in developing intelligent thought. If the environment rewards spending that energy on responding to other creatures, intelligence may be less important.


Given our only data point for complex life the data points toward intelligent life developing if given enough time; however, it took a very long time and shifts in the dominant types of complex life on the planet before it took place.

Given that we have no other data points I think it's virtually impossible to say. It's entirely possible that most planets reach a state of equilibrium and kinda stagnate until something kills off everything.

It's also possible that most planets with earth like histories and conditions develop intelligent creatures just like ours did.

I Don't think intellignet life must develop on any given planet with complex life. I do think it must develop on a planet, given an extremely large amount of planets with complex life

If you haven't seen it before the Drake Equation May help you make some loose estimates. Although it's not very scientific IMO


I like and agree with Tim B's answer and I've only skimmed over the rest.

To Tim Bs answer I would like to add that life and living systems are entropy engines that push the 4th law of thermodynamics forward and create more entropy.

Evolution through genetic modification allows living systems to exploit available chemical (I mean both food and mineral sources like petroleum) and radiation (eg sunlight) energy sources. For example there are strains of fungus that scientists have under investigation for cleaning up petroleum spills, we find living cells even in the hearts of glaciers and in the black depths of the ocean there are geothermal vents teeming with life.

So, natural selection is the mechanism by which life changes absolutely but to really understand the process we look to physics and the 4th law of thermodynamics. This law which is complicated states in part that energy systems will tend towards a state of maximum disorganization or lowest energy.

Our earth or more specifically its biosphere is an open energy system. It receives energy from the sun and also the earths molten core. Over millions of years the original self replicating molecules that most likely formed in pools around volcanic activity have developed more and more complex ways of accessing the energy stored in molecules. Along the way it has also developed ways of storing and protecting that energy and also developed ways of designing and building specific function into molecules like storing information, poisoning something that tries to eat it, envenoming prey or attackers, signaling between cells etc...

While this apparent complexity may appear to run against this idea of entropy and disorder keep in mind that the biosphere is always getting more energy bathed in solar radiation and heated by the earths core. As organisms become more complex and require more types of cells and molecules to govern them entropy increases as these metabolic demands require more calories to carry out. As organisms evolved from the original prokaryotes their ability to branch out and exploit energy sources wherever they possibly could (generating more entropy) has been the push force of evolution.

With that said I think that self aware tool using intelligence IS selected for by evolution but with a giant caveat. After all we are pumping hydrocarbons out of the earth to burn them. As a result of our ability to exploit nuclear and hydrocarbon fuels our population has exploded. (ENTROPY!) However the giant caveat is that tool using self awareness probably has a relatively low probability of occurring. It requires a social species that has a body with the fine motor skills to create tools and needs on the fly flexibility in its approach to solving food acquisition. This requires a sophisticated metabolically expensive brain that can communicate with other brains of it's type and generally be aware of what those other brains may know. My point is that a lot of branches of the tree of life are probably never going to generate anything like the intelligence you and I possess and it's conceivable that on other planets where life exists there have never been or ever will exist self aware tool using species like H Sapiens. So for entropy if it were a thinking being then a self aware tool using species like us is a lot like winning the lottery.


**When you say " With "intelligence" I intend a life form capable of ask itself a question like the one I'm submitting right now."**Even on a sigle webpage , the one I am viewing there is the same fascination with intelligence - Could plants develop intelligence?

Would spacefaring aliens have to be roughly as intelligent as humans? Does intelligence necessarily lead to an abstract language? Would it be possible for a single celled organism to evolve intelligence? Would it be possible for a planet orbiting a blue supergiant to develop intelligent life? Building a planet favorable to the evolution of intelligent life

Who is asking and who will answer? Members of a species who have first of all learn t a language , letters... ABCD..then they all agree upon a word and its meaning Intelligence ..and who because they cant communicate with other species , don't understand their lives , cant experience living IN their bodies EX water, rocks, plants, animals everything other than humans ...they all agree and suffer from a common psychosis (and thus appear normal to each other) that we are intelligent despite doing nothing more than surviving and reproducing like all other species on a grand scale..it you observe planet earth from s different plant or you observe the ever appearing and dying members on a long timescale.. say of hundred, thousand or million years. So i guess your question and the underlying human fascination with the so called human intelligence is on a different plane same as bacteria communicating among themselves when they have multiplied beating your immune system, leaves when they have made food by photo synthesis, animals when they have found grass to eat or preyed on another.They might be asking the same question, why do you assume that the only communication is verbal or written like I am typing to respond, why it cant be any other not understood by us ?

Point I want to make is when all humans appear to be doing- surviving and reproducing is the same as all other creatures are doing.. what is the point of saying that we are intelligent.. or more intelligent..or as we like to hypnotize collectively... most intelligent...Well other creatures seems to be accomplishing the same goals without expending so much of their resources..like we do..May be our fascination with intelligence and its search everywhere is because we might be lacking in it...we are not born intelligent...we have to learn how to survive and reproduce unlike other creatures..So even if we have agreed to call that faculty intelligence, who are more intelligent? Ones who are born with it we call instincts or the one who has to learn it..the intelligent?

Unless and until we can discuss the topic of intelligence with other organisms living on this planet who have evolved together with us and are as successful in surviving and reproducing as we are,till then all discussions are mere inter species discussion best we can call shits of the brain.

  • $\begingroup$ This is difficult to read. Can you please format it? Paragraphs etc. will help a lot. $\endgroup$ – Hohmannfan Oct 15 '16 at 21:25
  • $\begingroup$ So...would...conventional..sentences...and...punctuation...? $\endgroup$ – JDługosz Oct 17 '16 at 18:32

Intelligence will always increase over time. This is because evolution works in small increments whether positive or negative. An animal that is less intelligence fairs worse than one with more intelligence while other major fitness aspects will either increment in small amount which cannot supercede intelligence or there will be a huge leap which can only sustain a drop of intelligence to some level against it's competitors, but again intelligence kicks in and the small increments take over and again rise so you get a fairly stable continuous increase over time.

As far as the upper limits of this... I'm of the idea there is no upper limits because as intelligence increases so will energy rich sources of food which will allow this to continue on indefinitely.

The problem is that this doesn't quite matter, because all the stars that are likely to support life aren't able to support complex life long enough for human level intelligence to evolve through this method (or at least I don't think so. I haven't run any numbers, but it seems to be right given how much time is left on Earth compared with where we are.) So if you're talking human level intelligence then no, Human intelligence is not the normal product of evolution. Humans evolved through a few happenstances occuring that kicked our intelligence way down the field that we can only maintain due to a few small tricks, like cooking food, being predator/preys, being social, etc all of which combined to push human intelligence up.

  • $\begingroup$ "An animal that is less intelligence fairs worse than one with more intelligence" - Disagree: reduce intelligence, maximize reproduction. See cockroach. Or for a non-animal example, the arguably most successful lifeform: bacteria. $\endgroup$ – called2voyage Oct 14 '16 at 17:28
  • $\begingroup$ @called2voyage arguable only if we're talking about 1 species overall, but we're talking about all species with a max intelligence raising over time. Pressure forces this to occur whether cockroaches and bacteria exist or not. $\endgroup$ – Durakken Oct 14 '16 at 17:39

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