# Evolution of intelligence in other habitable planets? **URL:** \ **Category:** Great Debates\ **Created:** [August 30, 2012, 1:25pm UTC](https://boards.straightdope.com/t/evolution-of-intelligence-in-other-habitable-planets/633138 "2012-08-30T13:25:26Z")\ **Posts on this page:** 19\ **Page:** 3
**Author:** ![Blaster\_Master](https://avatars.discourse-cdn.com/v4/letter/b/cab0a1/32.png) [@Blaster\_Master](https://boards.straightdope.com/u/Blaster_Master)\ **Post date:** [August 31, 2012, 3:57pm UTC](https://boards.straightdope.com/t/evolution-of-intelligence-in-other-habitable-planets/633138/41 "2012-08-31T15:57:15Z")
I think this is one of those questions that really only comes up with a lot of speculation. After all, we only have one example of life and we’re not even sure if life might exist, or existed in the past, on other planets/moons in our own solar system. Even in our example, we have a remarkable number of variables interacting and it’s difficult to know exactly how just how important many of them are. For instance, we have a relatively large moon, it seems many people consider it to be an important part of life evolving on Earth. How much impact would it have had on evolution here if it were bigger or smaller or we had multiple moons or no moon at all? What if days were longer or shorter or our axis had a different tilt? What if the sun was a different kind of star or were were at a different distance from it or had a different type of orbit? How much impact do the other planets, particularly the larger one and their placement have on life? Even if we lucked out and got just the right mix of all of that, we still may have gotten lucky with impacts and sun stability and all that sort of stuff. Sure, life is resilient now and exists in just about everywhere on the planet, but how much of that is due to life being inherently resilient or life being able to gradually evolve to become resilient to those different conditions? But for the sake of argument, let’s just say it’s a given life exists in countless places throughout the universe, that still doesn’t really give us any insight into the evolution of intelligence. Yes, there are other species that are more or less intelligent on this planet, but we still only have one example of a species that has even basic technology, fire, the wheel, etc. Maybe it’s quite common that one species will, given long enough, develop advanced intelligence and technology or maybe it’s extremely rare and we just got lucky. But let’s say for the sake of argument that human levels of intelligence is still fairly common. That doesn’t really mean much because now you don’t just have evolutionary pressure, but also cultural pressures in applying that technology. What if another similar society ended up with values akin to the Amish, shunning certain advancements in technology, except at various other levels of technology. Maybe a similar culture would be considerably more warlike and consistently kill eachother off forcing them to spend their resources just on reproduction and weapons and not on other applications or maybe our particular warlike nature is part of what helped us develop the technology we have. Or maybe a society just has different aspirations, like solving issues akin to world hunger and poverty before pursuing other advanced technologies like space exploration. But really, until we start finding other planets that have life on them, or run into other intelligent beings, either extra terrestrial or here on Earth, how do we really weigh the probabilities? ---
**Author:** ![Voyager](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voyager/32/133_2.png) [@Voyager](https://boards.straightdope.com/u/Voyager)\ **Post date:** [August 31, 2012, 5:01pm UTC](https://boards.straightdope.com/t/evolution-of-intelligence-in-other-habitable-planets/633138/42 "2012-08-31T17:01:22Z")
> [@Acid\_Lamp](#): > > That isn’t just a speculative fiction either. In the late cretaceous we already had medium sized, bipedal, social pack hunters with grasping hands and decently large brains. Without the extinction event it is very plausible that these sort of animals might well have developed into an intelligent civilization. In one of the many books I have about dinosaurs there is an artist’s rendition of an intelligent one, slightly evolved from those you mention. In Stephen Baxter’s “Evolution” he has a small section on a pack of dinosaurs just past the brink of intelligence who get wiped out by the asteroid. So I didn’t make the concept up. ---
**Author:** ![ryanl](https://avatars.discourse-cdn.com/v4/letter/r/b487fb/32.png) [@ryanl](https://boards.straightdope.com/u/ryanl)\ **Post date:** [August 31, 2012, 5:17pm UTC](https://boards.straightdope.com/t/evolution-of-intelligence-in-other-habitable-planets/633138/43 "2012-08-31T17:17:03Z")
A stressed out middle-management T-Rex pulling late nights at the office? I wonder if the dominance of certain species has a tendency to lessen the selective pressures on traits such as intelligence. After all, why devote precious resources on an energy-hungry brain if size and big teeth are enough to ensure your spot at the ecological apex? ---
**Author:** ![levdrakon](https://avatars.discourse-cdn.com/v4/letter/l/49beb7/32.png) [@levdrakon](https://boards.straightdope.com/u/levdrakon)\ **Post date:** [August 31, 2012, 5:57pm UTC](https://boards.straightdope.com/t/evolution-of-intelligence-in-other-habitable-planets/633138/44 "2012-08-31T17:57:30Z")
Is it correct to say “intelligence only evolved once?” We also have Neanderthals and Flores hominids. Stepping back along the great ape family tree it seems there were a multitude of intelligent, social tool users. We’ve also got our extant great apes, which could eventually result in more intelligent species. Hasn’t intelligence evolved multiple times just on Earth? ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [August 31, 2012, 7:12pm UTC](https://boards.straightdope.com/t/evolution-of-intelligence-in-other-habitable-planets/633138/45 "2012-08-31T19:12:05Z")
> [@Chimera](#): > > And how would we know when they were made and used … Same way fossils are dated - by the dating the layers in which they are found. ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [August 31, 2012, 8:16pm UTC](https://boards.straightdope.com/t/evolution-of-intelligence-in-other-habitable-planets/633138/46 "2012-08-31T20:16:37Z")
> [@Acid\_Lamp](#): > > That isn’t just a speculative fiction either. In the late cretaceous we already had medium sized, bipedal, social pack hunters with grasping hands and decently large brains. Without the extinction event it is very plausible that these sort of animals might well have developed into an intelligent civilization. Dogs are highly intelligent. So are birds. And dolphins. Raccoons are intelligent and have grasping hands. None of them seem to be evolving towards ever-greater intelligence. There’s a general misconception that evolution is the progression from simple to complex, from dumb to smart, or in general from a ‘lower’ form of life to a ‘higher’ form of life. That’s just not the case. Evolution is a random walk influenced by competitive pressure. T-Rex’s ancestors had functional hands, but they atrophied because natural selection pushed T-Rex in another direction. The most successful species on the planet in terms of overall mass and numbers are probably squid, which are quite intelligent but have remained at approximately the same level of intelligence for millions of years. I see no reason to believe that if dinosaurs had survived we’d have a dinosaur civilization now. Birds are close to dinosaurs. They’re smart, they use tools, they travel in flocks, and they can problem solve. But there hasn’t been any progression towards a technological bird civilization. Of course, you never know. Maybe some evolutionary pressure would have driven one or more species of dinosaur towards high intelligence. Or perhaps they would be like alligators - changing size due to changes in oxygen content in the atmosphere, but otherwise staying pretty much the same. We’ll never know the road not taken, but we can say there’s no universal force we’ve seen so far that pushes life on a planet in a particularly intelligent direction. Intelligence has a number of evolutionary drawbacks, too. A large brain consumes a lot of energy. It’s vulnerable to attack and damage. A large head makes it harder to give birth, or to have many babies. Human children are absolutely helpless and dependent on the mother for a long time until their brains can adapt to the knowledge gathered after birth and become useful. Intelligence gives us the power to modify our environment, but also to destroy on a wide scale. So who knows? Maybe you need exactly the right, and fairly rare conditions for high intelligence to develop, and maybe even then it’s a one in a million shot. We just don’t know. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [August 31, 2012, 10:05pm UTC](https://boards.straightdope.com/t/evolution-of-intelligence-in-other-habitable-planets/633138/47 "2012-08-31T22:05:10Z")
> [@Sam\_Stone](#): > > There’s a general misconception that evolution is the progression from simple to complex, from dumb to smart, or in general from a ‘lower’ form of life to a ‘higher’ form of life. That’s just not the case. Except that the fossil record shows unambiguously that it is the case. The average level of intelligence of life on Earth, as measured by the degree of cephalisation, has shown a very clear upward trend over time. The average level of intelligence of the organisms within any ecological niche has shown an even more marked upward trend over time; so, for example, the intelligence of leaf eaters or egg eaters today is much higher than it was in the Cretaceous, and the average intelligence of predators is much higher. The \*rate \*of intelligence increase also shows a very clear upward tend over time: so while the intelligence of leaf eaters today is much higher than it was in the in the Eocene, the Eocene leaf eaters were in turn much smarter than the Cretatceous leaf eaters who were in turn orders of magnitude smarter than Permian leaf eater. The intelligence of the smartest species on the planet shows a continuous series of upward leaps. Intelligence really does seem to be a case where evolution moves continually upwards. It isn’t true that any individual lineage will become continually smarter, but it is true for life as a whole. Of course evolution isn’t the only trait in which evolution shows a progression from simple to complex sensory organs are another one, and there are several others. That seems to be because intelligence, like sensory organs, is itself a very strong selector for survival of \*other \*species. Once a predator becomes smart, then prey animals have a survival advantage if they, too, become smart. As prey becomes smarter, the predators themselves need to become smarter to survive. IOW intelligence drive the evolution of intelligence in \*other \*species, which forces a continual evolutionary increase in intelligence. None of this means that intelligence is the \*only \*way to cope with intelligence. A tortoise is quite capable of dealing with a much smarter predator simply by virtue of having a shell. But such adaptations reduce ecological flexibility in a manner that organisms that cope via higher intelligence don’t suffer from. As a result the organism that prosper as new niches open up tend to be the smarter ones. So over time. while not all individual lineages get smart, the average and the upper 95th percentile both increase more-or-less continually. Which is why, if there is life on other planets, it is highly plausible that it will become intelligent eventually. It’s not certain, there may be factors that preclude the evolution of intelligence, but it is likely. Assuming that there are no factors that preclude intelligence such as an inability to grow large, then intelligence should continue to increase in any biosphere. And once a few organisms reach the stage of being able to communicate abstract ideas, there ceases to be any biological limit on intelligence. At that stage intelligence should be able to increase indefinitely. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [August 31, 2012, 10:23pm UTC](https://boards.straightdope.com/t/evolution-of-intelligence-in-other-habitable-planets/633138/48 "2012-08-31T22:23:55Z")
> [@Sam\_Stone](#): > > A large brain [is] vulnerable to attack and damage. Not particularly. Brains are the most well protected organs in the body. Very few, if any, kills of animals occur specifically because of brain damage. Usually predators attack the abdominal organs, the legs or the neck, none of which are affected by brain size. If large brains really were more vulnerable, we would expect to see more mammals dying of brain injuries than reptiles, more reptiles than amphibians and so forth. But that isn’t the case. Brains just aren’t an organs that predators target. > [@](#): > > A large head makes it harder to give birth, or to have many babies. Human children are absolutely helpless and dependent on the mother for a long time until their brains can adapt to the knowledge gathered after birth and become useful. But all that is due to bipedalism. It has nothing to do with brain size _per se_. Apes have larger brains than monkeys, and monkeys larger than bears. But apes don’t have a harder time giving birth than monkeys or bears, nor do they have more helpless babies. Humans have evolved into a corner where we adopted bipedal stance and \*then \*became intelligent, which leads to the problems you describe. They aren’t problems of intelligence, they are problems of bipedalism. Deer have babies about the same size as humans, despite being much smaller, because the pelvic opening is much wider. A doe could deliver a human infant with little problem. There’s no doubt that intelligence has some drawbacks, just not these ones. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [August 31, 2012, 10:26pm UTC](https://boards.straightdope.com/t/evolution-of-intelligence-in-other-habitable-planets/633138/49 "2012-08-31T22:26:54Z")
> [@Blake](#): > > A doe could deliver a human infant with little problem. Let’s hope that’s an experiment that is never carried out! 🙂 ---
**Author:** ![Voyager](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voyager/32/133_2.png) [@Voyager](https://boards.straightdope.com/u/Voyager)\ **Post date:** [August 31, 2012, 11:30pm UTC](https://boards.straightdope.com/t/evolution-of-intelligence-in-other-habitable-planets/633138/50 "2012-08-31T23:30:58Z")
> [@Sam\_Stone](#): > > Dogs are highly intelligent. So are birds. And dolphins. Raccoons are intelligent and have grasping hands. None of them seem to be evolving towards ever-greater intelligence. I don’t know about that. I had a border collie mix who could generalize, be tricky, and plan ahead in order to fool me. For example, we taught him to sit before he crossed at the corner. He abstracted this into sitting in the middle of the street to tell us he wanted to cross. Dogs have limited vocal ability and even more limited grasping ability so I’m not saying they are on the verge. > [@](#): > > There’s a general misconception that evolution is the progression from simple to complex, from dumb to smart, or in general from a ‘lower’ form of life to a ‘higher’ form of life. That’s just not the case. Evolution is a random walk influenced by competitive pressure. That has nothing to do with the present case. Unless you think that there is some reason greater intelligence can’t arise randomly, the contention would be that it produces a competitive advantage in animals possessing it. That could be evading predators, being a better predator, or any number of factors. Obviously intelligence isn’t the only useful trait, it is just one of them. > [@](#): > > T-Rex’s ancestors had functional hands, but they atrophied because natural selection pushed T-Rex in another direction. The most successful species on the planet in terms of overall mass and numbers are probably squid, which are quite intelligent but have remained at approximately the same level of intelligence for millions of years. Let’s be clear that no one is talking about a T rex becoming intelligent. There is no reason for that to be an advantage. The thought was that smaller predators, working cooperatively in packs were more likely to be heading in that direction. There is some thought that our intelligence is partly a result of the advantage of better reading social cues - no reason that wouldn’t work for pack dinosaurs also. Clearly the ability to communicate and plan during hunts would be advantageous also. > [@](#): > > I see no reason to believe that if dinosaurs had survived we’d have a dinosaur civilization now. Birds are close to dinosaurs. They’re smart, they use tools, they travel in flocks, and they can problem solve. But there hasn’t been any progression towards a technological bird civilization. Birds have very severe weight restrictions, and a larger brain would put a bird at a selective disadvantage long before intelligence could evolve to make use of it. And of course no one is saying it would have happened, just that it might have happened. Unless you think that only mammals, or only primates, could evolve intelligence. > [@](#): > > Intelligence has a number of evolutionary drawbacks, too. A large brain consumes a lot of energy. It’s vulnerable to attack and damage. A large head makes it harder to give birth, or to have many babies. Human children are absolutely helpless and dependent on the mother for a long time until their brains can adapt to the knowledge gathered after birth and become useful. Intelligence gives us the power to modify our environment, but also to destroy on a wide scale. So who knows? Maybe you need exactly the right, and fairly rare conditions for high intelligence to develop, and maybe even then it’s a one in a million shot. We just don’t know. There is evidence that some dinosaurs were herd animals, and that children stayed with the herd and were thus protected, which would give them room to grow. Carnivores would likely have plenty of spare energy, especially if slowly increasing intelligence made them better hunters. All arguments against the acquisition of intelligence apply to us in spades, of course. And it only has to happen, in fact is only likely to happen, once. ---
**Author:** ![Voyager](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voyager/32/133_2.png) [@Voyager](https://boards.straightdope.com/u/Voyager)\ **Post date:** [August 31, 2012, 11:34pm UTC](https://boards.straightdope.com/t/evolution-of-intelligence-in-other-habitable-planets/633138/51 "2012-08-31T23:34:13Z")
> [@levdrakon](#): > > Is it correct to say “intelligence only evolved once?” We also have Neanderthals and Flores hominids. Stepping back along the great ape family tree it seems there were a multitude of intelligent, social tool users. We’ve also got our extant great apes, which could eventually result in more intelligent species. > > Hasn’t intelligence evolved multiple times just on Earth? Isn’t it more likely that there was speciation starting with an intelligent species into several other species of differing levels of intelligence, with selection favoring the more intelligent ones? That we all came from Africa seems to indicate intelligence evolved only once, but I realize this is still somewhat controversial. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [September 1, 2012, 1:03am UTC](https://boards.straightdope.com/t/evolution-of-intelligence-in-other-habitable-planets/633138/52 "2012-09-01T01:03:30Z")
> [@levdrakon](#): > > Is it correct to say “intelligence only evolved once?” We also have Neanderthals and Flores hominids. Stepping back along the great ape family tree it seems there were a multitude of intelligent, social tool users. We’ve also got our extant great apes, which could eventually result in more intelligent species. > > Hasn’t intelligence evolved multiple times just on Earth? Define “intelligence”. But the various species of _Homo_ are all very closely related, and I don’t think it makes sense to consider the different species within that genus to have evolved “intelligence” independently. One could make a good case that those various populations should all be the same species anyway. It’s just that the species definition we adopted tends to say otherwise. That is not to say that we couldn’t just as easily, and just as accurately, have different working definition. The common ancestor of all _Homo_ species was a tool user. It would be better to look for different lines of decent from non-tool using ancestors to say that “intelligence” evolved more than once. ---
**Author:** ![Bookkeeper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bookkeeper/32/281_2.png) [@Bookkeeper](https://boards.straightdope.com/u/Bookkeeper)\ **Post date:** [September 4, 2012, 4:18am UTC](https://boards.straightdope.com/t/evolution-of-intelligence-in-other-habitable-planets/633138/53 "2012-09-04T04:18:13Z")
> [@Blake](#): > > Except that the fossil record shows unambiguously that it is the case. > > The average level of intelligence of life on Earth, as measured by the degree of cephalisation, has shown a very clear upward trend over time. The average level of intelligence of the organisms within any ecological niche has shown an even more marked upward trend over time; so, for example, the intelligence of leaf eaters or egg eaters today is much higher than it was in the Cretaceous, and the average intelligence of predators is much higher. The \*rate \*of intelligence increase also shows a very clear upward tend over time: so while the intelligence of leaf eaters today is much higher than it was in the in the Eocene, the Eocene leaf eaters were in turn much smarter than the Cretatceous leaf eaters who were in turn orders of magnitude smarter than Permian leaf eater. The intelligence of the smartest species on the planet shows a continuous series of upward leaps. > > Intelligence really does seem to be a case where evolution moves continually upwards. It isn’t true that any individual lineage will become continually smarter, but it is true for life as a whole. Of course evolution isn’t the only trait in which evolution shows a progression from simple to complex sensory organs are another one, and there are several others. > > That seems to be because intelligence, like sensory organs, is itself a very strong selector for survival of \*other \*species. Once a predator becomes smart, then prey animals have a survival advantage if they, too, become smart. As prey becomes smarter, the predators themselves need to become smarter to survive. IOW intelligence drive the evolution of intelligence in \*other \*species, which forces a continual evolutionary increase in intelligence. > > None of this means that intelligence is the \*only \*way to cope with intelligence. A tortoise is quite capable of dealing with a much smarter predator simply by virtue of having a shell. But such adaptations reduce ecological flexibility in a manner that organisms that cope via higher intelligence don’t suffer from. As a result the organism that prosper as new niches open up tend to be the smarter ones. So over time. while not all individual lineages get smart, the average and the upper 95th percentile both increase more-or-less continually. > > Which is why, if there is life on other planets, it is highly plausible that it will become intelligent eventually. It’s not certain, there may be factors that preclude the evolution of intelligence, but it is likely. Assuming that there are no factors that preclude intelligence such as an inability to grow large, then intelligence should continue to increase in any biosphere. > > And once a few organisms reach the stage of being able to communicate abstract ideas, there ceases to be any biological limit on intelligence. At that stage intelligence should be able to increase indefinitely. But this is consistent with the random walk evolutionary pattern noted by **Sam Stone**. For something like intelligence, variation is constrained, as there can’t be negative intelligence, so random variation over time will always push the average intelligence level higher, as extremes can only happen at the upper limit, never at the lower limit. (Stephen Jay Gould had an excellent essay in one of his books on this topic, but I can’t remember which one and don’t have access to my copies at the moment.) ---
**Author:** ![Cheshire\_Human](https://avatars.discourse-cdn.com/v4/letter/c/5f8ce5/32.png) [@Cheshire\_Human](https://boards.straightdope.com/u/Cheshire_Human)\ **Post date:** [September 4, 2012, 8:23pm UTC](https://boards.straightdope.com/t/evolution-of-intelligence-in-other-habitable-planets/633138/54 "2012-09-04T20:23:43Z")
> [@Bookkeeper](#): > > But this is consistent with the random walk evolutionary pattern noted by **Sam Stone**. For something like intelligence, variation is constrained, as there can’t be negative intelligence, so random variation over time will always push the average intelligence level higher, as extremes can only happen at the upper limit, never at the lower limit. (Stephen Jay Gould had an excellent essay in one of his books on this topic, but I can’t remember which one and don’t have access to my copies at the moment.) Yes and no. I regularly do computer simulations\*\*\*\*\* of things that are constrained (you can’t get lower than zero) at one extreme, but are unconstrained at the other extreme, using random numbers (sometimes generated by the pseudorandom routine built into the language, other times true random, generated by a variety of methods), and they only walk so far from the constrained extreme, before there is no longer any pressure to go higher, so they don’t. When you don’t get a zero, let alone an impossible negative, in a few billion iterations, the constraint effectively stops being a source of upward pressure. Therefore, **Blake** ’s post effectively describes a continuing upward pressure (natural selection favoring intelligence) that isn’t _just_ because the lower extreme is constrained. An example: A human child with zero intelligence is dead meat. A human child at an IQ of 50 would be dead meat if it’s society couldn’t afford to support it. Effectively, the constraint on the lower extreme rises, as the average rises, so the lower limit is _not_ constrained by it’s inability to go below zero. It’s constrained by society’s inability to support anything below an ambiguous lower limit that’s defined by its distance below the average. **Blake** and **Sam Stone** are _not_ describing situations that are at all different. They’re just coming at it from different directions. Ultimately, they wind up in the same place. \*\*\*\*\* It’s a hobby of mine. You, too, have a supercomputer sitting on your lap or desk. The cheapest laptop netbook you can buy, easily beats a Cray XMP… ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [September 4, 2012, 8:33pm UTC](https://boards.straightdope.com/t/evolution-of-intelligence-in-other-habitable-planets/633138/55 "2012-09-04T20:33:02Z")
> [@John\_Mace](#): > > The common ancestor of all _Homo_ species was a tool user. It would be better to look for different lines of decent from non-tool using ancestors to say that “intelligence” evolved more than once. Not to be persnickety but this isn’t known yet. We are really better described as part of the Pan line e.g. Pan Sapiens. It may be that the common ancestor with other “homo” branches was not a tool user. But “intelligence” is not a ideal under all circumstances, our brain eats a LOT of calories and if you are in an area without much food it would be a huge disadvantage to have such a power hungry mind. Note that outside of simple tools we were living hand to mouth like every other critter until the last, tiny section of our existence. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [September 5, 2012, 5:08am UTC](https://boards.straightdope.com/t/evolution-of-intelligence-in-other-habitable-planets/633138/56 "2012-09-05T05:08:36Z")
One thing that could constrain the future development of intelligent life in the galaxy is the increasing abundance of metals. As the galaxy gets older more supernovae add more planet-building elements into the interstellar medium. This means that new stars have more material to make planets from. Not such a good thing, because more planet building material means heavier planets on average, so that younger systems have more hot jupiters and superterrestrials which are not really much good for developing life, and probably _exclude_ terrestrial planets from many systems. As the galaxy gets older there will probably be fewer and fewer Earth-like worlds; the great season for the emergence of life as we recognise it may already have passed. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [September 5, 2012, 10:16am UTC](https://boards.straightdope.com/t/evolution-of-intelligence-in-other-habitable-planets/633138/57 "2012-09-05T10:16:18Z")
> [@Bookkeeper](#): > > But this is consistent with the random walk evolutionary pattern noted by **Sam Stone**. For something like intelligence, variation is constrained, as there can’t be negative intelligence, so random variation over time will always push the average intelligence level higher, as extremes can only happen at the upper limit, never at the lower limit. This can be readily refuted either theoretically or by observation. Theoretically, if variation is constrained to zero that can only provide an upward force to random variation for values close to the maximum rate of change. So, for example, if intelligence increases at a maximum rate of 100 units per generation, then the constraint will increase intelligence up to at most a few thousand units. Once a population has intelligence greater than, say, 10, 000 units then in any given generation random chance is just as likely to cause a reversion downwards as it is upwards. The constraint caused by a lower limit vanishes once the lower limit is further away than the maximum change rate. By observation we can refute it simply by looking at any other feature that has an absolute limit of zero. The number of legs is a good example. If what you said above were correct, we would expect the mean number of legs of organisms on Earth to show the same exponential increase that we see with intelligence. IOW, starting from the Cambrian we should now be seeing organisms with billions of legs. Of course we don’t see any such things. If anything the number of legs decreases over time. We could say the same about genome size or number of life stages or any of literally millions of other biological traits that can’t have negative values. ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [September 5, 2012, 1:29pm UTC](https://boards.straightdope.com/t/evolution-of-intelligence-in-other-habitable-planets/633138/58 "2012-09-05T13:29:22Z")
If grains of sand on the beach were planets, and say every mile or so of beach one of these planets had intelligent life. We would never find it from our grain of sand. We would have to travel literaly for millions of years in spaceships much faster than we have today to conduct even a most basic search for other forms of life. We live less than a hundred years. A true search is really not even worth contemplating beyond what we can do with telescopes. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [September 5, 2012, 4:52pm UTC](https://boards.straightdope.com/t/evolution-of-intelligence-in-other-habitable-planets/633138/59 "2012-09-05T16:52:13Z")
> [@rat\_avatar](#): > > Not to be persnickety but this isn’t known yet. We are really better described as part of the Pan line e.g. Pan Sapiens. It may be that the common ancestor with other “homo” branches was not a tool user. Actually it is, because one of the defining features of early _Homo_ is stone tool use (which I should have said in that earlier post instead of just “tool”). If we stick to the general term (no pun intended), there is no way we would put a non-tool user in the genus _Homo_. No way. As for tool use in general, it’s a near certainty that all our hominin ancestors used some sort of tools, since chimps do, too. We don’t have direct evidence, but it would be astounding if it weren’t so. [Previous page](https://boards.straightdope.com/t/evolution-of-intelligence-in-other-habitable-planets/633138.md?page=2)