# How many planets in our galaxy harbor intelligent life? **URL:** \ **Category:** In My Humble Opinion\ **Created:** [July 30, 2015, 2:37pm UTC](https://boards.straightdope.com/t/how-many-planets-in-our-galaxy-harbor-intelligent-life/726578 "2015-07-30T14:37:21Z")\ **Posts on this page:** 10\ **Page:** 4
**Author:** ![Lucas\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lucas_jackson/32/303_2.png) [@Lucas\_Jackson](https://boards.straightdope.com/u/Lucas_Jackson)\ **Post date:** [August 1, 2015, 6:05pm UTC](https://boards.straightdope.com/t/how-many-planets-in-our-galaxy-harbor-intelligent-life/726578/62 "2015-08-01T18:05:54Z")
> [@Thoo1938](#): > > I would say Just the one. The planet Earth. Otherwise there would be humans living elsewhere as well. You do realize the universe is a pretty big place, right? ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [August 1, 2015, 6:41pm UTC](https://boards.straightdope.com/t/how-many-planets-in-our-galaxy-harbor-intelligent-life/726578/63 "2015-08-01T18:41:36Z")
> [@cmyk](#): > > Which give us a “Wisdom of the Crowd” estimate of **47,697,848** intelligent races within our galaxy alone. Surowiecki’s “Wisdom of Crowds” concept is an inflation of the significance of basic frequentist statistics, e.g. that the statistics on reasonably credible estimates will tend to converge to a normally distributed function, along with some handwaving about how a group of random individuals of no particular competence become “experts” in the aggregate. Many of the examples he gives in his book are dubious or just flat-out wrong, especially the supposedly punitive response of the stock market at Morton Thiokol because of the role of the SRM in the _Challenger_ failure which I debunk [POST=12753543]here[/POST]. In this case, the way you’ve created your sample distribution isn’t even; it jumps by orders of magnitudes and not evenly at that, so you really need to weigh your estimates by the spread of range it covers. But the estimates themselves are bunk, because there isn’t any way to evaluate a credible estimate as there is with a jar of gumballs. But there is an even deeper problem with the question: what counts as “intelligence”? We tend to think that we have an intuitive understanding of what that means, but even that definition is constantly shifting as we discover that many different types of animals have greater cognitive abilities than previously suspected. And while we view ourselves as being the top of our particular ecosystem in terms of intellect, we may well be insects compared to a more highly developed alien species to the point that they wouldn’t regard anything we does as more than mere “instinct”. And the ways in which intelligence could manifest may be very different; we think we’re clever for having developed writing, art, discrete mathematics, et cetera, but an intelligent alien species may have little use for any of this, having other and very different forms for recording or conveying information, different recreation and creative methods, different ways of viewing the physical world that don’t fit into our system of largely integer counting mathematics, and so forth. I think we can most generally identify intelligence as an evolutionary strategy to improve fitness by deliberately adapting our environment to our needs(e.g. using tools or recruiting other species for labor or nutrition value) and modifying ourselves (selective breeding, reproductive medicine, genetic engineering). However, these general constraints may provide the sufficient by not necessary conditions to demonstrate what we would consider “true” intellect. I think, however, we can observe that the ability to use tools or perform complex feats of communication (albeit not at the same level of elaborate grammar as modern _Homo sapiens_) has arisen independently in many difference species in widely separated genus, e.g. primates, parrots and crows, some cephalopods, bears, et cetera. On that basis, we can see that as an evolutionary strategy the development of intelligence has benefit and we would expect the same development elsewhere in proportion to the presumed distribution of life elsewhere in the universe, about which we also have no evidence but we can observe that the essential constituents are common and conditions under which self-organizing chemical systems can function are probably not infrequent. The assumption that the precise conditions of Earth are a required precursor for any kind of life to develop is just a form of special pleading, a just-so story with no other purpose than to make us seem somehow special. That life has managed to find a viable niche in every possible terrestrial environment except the very high atmosphere or inside of a volcano argues for life to be robust and almost infinitely adaptable to any conditions under which normal organic chemistry can function (and this assumes that alien life would use an organic chemistry base, which is reasonable but shouldn’t be taken as an exclusive requirement). So, we’re probably either a unique case–life, and intelligent life only occurred once due to some astronomically special confluence of events–or the occurrence of life, and propensity to some degree of intelligence as a successful evolutionary strategy, is very common (on the order of millions to billions of incidences). However, the degree to which other life develops intelligence as we could possibly recognize or interact with it is a complete unknown, and even speculative guesses from a thousand “experts” wouldn’t credibly inform us on the topic. The notion of an alien species of comparable intelligence, much less a similar morphological body plan or comprehensible society, is nothing more than a convenience to science fiction authors and screenwriters. Any truly alien intelligent life is likely to be so different as to be nearly incomprehensible or perhaps even unrecognizable. Stranger ---
**Author:** ![escaped](https://avatars.discourse-cdn.com/v4/letter/e/848f3c/32.png) [@escaped](https://boards.straightdope.com/u/escaped)\ **Post date:** [August 1, 2015, 7:07pm UTC](https://boards.straightdope.com/t/how-many-planets-in-our-galaxy-harbor-intelligent-life/726578/64 "2015-08-01T19:07:29Z")
Dozens of races exist in the galaxy 😕but after getting video transmission of giligans island they decide its not worth it to make contact with us. ---
**Author:** ![septimus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/septimus/32/410_2.png) [@septimus](https://boards.straightdope.com/u/septimus)\ **Post date:** [August 2, 2015, 12:32pm UTC](https://boards.straightdope.com/t/how-many-planets-in-our-galaxy-harbor-intelligent-life/726578/65 "2015-08-02T12:32:42Z")
> [@cmyk](#): > > According to the 84 votes we’ve polled, here’s the average as broken down below. > > … 5) Thousands 18 people think it’s ~1000 = **18,000** > > Which give us a “Wisdom of the Crowd” estimate of **47,697,848** intelligent races within our galaxy alone. ~1000 is a low estimate for “thousands.” Using slightly different numbers I get an arithmetic mean of 160 million. But is arithmetic mean the right mean to use? (How do they average juror’s financial offers in civil suits?) I find the geometric mean of Dopers’ guesses to be 620, and harmonic mean to be just 2.9. (To calculate these means I had to reject those answering Zero. Since a race that produced Archimedes and Einstein is surely intelligent, I’ll assume that the Zeros were just jokes about the frustration of American politics.) ---
**Author:** ![cmyk](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cmyk/32/3353_2.png) [@cmyk](https://boards.straightdope.com/u/cmyk)\ **Post date:** [August 2, 2015, 1:20pm UTC](https://boards.straightdope.com/t/how-many-planets-in-our-galaxy-harbor-intelligent-life/726578/66 "2015-08-02T13:20:03Z")
> [@Esox\_Lucius](#): > > I think a better example would be hiding the jar so that you can only see one gumball, and guessing how many others there are. It could be a thousand or it could be none. There’s no way to know. It’s more like knowing there’s a gumball globe filled with trillions of different colored gumballs. But you know there’s at least one blue gumball, then taking a guess as to how many other blue gumballs there might be. And you figure blue is one of the hardest colors to make. ---
**Author:** ![samclem](https://avatars.discourse-cdn.com/v4/letter/s/a9a28c/32.png) [@samclem](https://boards.straightdope.com/u/samclem)\ **Post date:** [August 2, 2015, 2:10pm UTC](https://boards.straightdope.com/t/how-many-planets-in-our-galaxy-harbor-intelligent-life/726578/67 "2015-08-02T14:10:17Z")
None. ---
**Author:** ![John\_DiFool](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_difool/32/19543_2.png) [@John\_DiFool](https://boards.straightdope.com/u/John_DiFool)\ **Post date:** [August 2, 2015, 2:20pm UTC](https://boards.straightdope.com/t/how-many-planets-in-our-galaxy-harbor-intelligent-life/726578/68 "2015-08-02T14:20:36Z")
> [@levdrakon](#): > > I went with 100s of thousands. Ask tomorrow, I may have changed my mind again. > > The whole Goldilocks Principle sort of makes sense, but you have to kind of want it to make sense. It’s not my favorite theory. Everything had to be juuuust right! Seems awfully anthropocentric to me. I don’t think Earth is that special. Our sun isn’t that special. Stars, rocky planets, water & organic molecules of all kinds abound. Solar systems are full of good life-making stuff. But the trick is to have your gene line(s) survive all the way from the time they emerge from the slime for the first time until they start building spaceships and other such toys. You can’t consider things strictly from such a purely space-centric view as the one above-the time dimension is the hardest one to navigate over a timeline of 500 million years+. Having the right conditions at the start is child’s play compared to that. The most illustrative way to simulate that would be to keep flipping a coin, over and over-heads your gene line lives, tails it dies (for whatever reason(s)). Get 100 heads in a row, and then get back to us. Even if it would require “only” 25 flips in a row, those remain pretty daunting odds, even if on any given planet there are several gene lines with potential (here in addition to us I think we have pachyderms, with their manipulative proboscids, and, if they had lived, certain smaller theropod dinosaur lines, some other primate lines, and…?). ---
**Author:** ![Esox\_Lucius](https://avatars.discourse-cdn.com/v4/letter/e/848f3c/32.png) [@Esox\_Lucius](https://boards.straightdope.com/u/Esox_Lucius)\ **Post date:** [August 2, 2015, 5:29pm UTC](https://boards.straightdope.com/t/how-many-planets-in-our-galaxy-harbor-intelligent-life/726578/69 "2015-08-02T17:29:01Z")
> [@escaped](#): > > Dozens of races exist in the galaxy 😕but after getting video transmission of giligans island they decide its not worth it to make contact with us. If they don’t fall for Maryann, they’re not worth knowing about. ---
**Author:** ![Esox\_Lucius](https://avatars.discourse-cdn.com/v4/letter/e/848f3c/32.png) [@Esox\_Lucius](https://boards.straightdope.com/u/Esox_Lucius)\ **Post date:** [August 2, 2015, 5:31pm UTC](https://boards.straightdope.com/t/how-many-planets-in-our-galaxy-harbor-intelligent-life/726578/70 "2015-08-02T17:31:30Z")
> [@cmyk](#): > > It’s more like knowing there’s a gumball globe filled with trillions of different colored gumballs. But you know there’s at least one blue gumball, then taking a guess as to how many other blue gumballs there might be. And you figure blue is one of the hardest colors to make. Right. At any rate, the original gumball exercise isn’t really applicable. ---
**Author:** ![marshmallow](https://avatars.discourse-cdn.com/v4/letter/m/df705f/32.png) [@marshmallow](https://boards.straightdope.com/u/marshmallow)\ **Post date:** [August 3, 2015, 1:44am UTC](https://boards.straightdope.com/t/how-many-planets-in-our-galaxy-harbor-intelligent-life/726578/71 "2015-08-03T01:44:42Z")
I think life itself is fairly common. I wouldn’t be surprised if there’s microscopic xenolife in our own solar system. But that’s as far as life goes most of the time. You can travel as far as you like and find millions of worlds covered in what amounts to slime. If there were any intelligent species they died a long time ago and didn’t stray far from their home planet, just like we probably won’t either. Think of the requirements of interstellar travel. You have to construct a self-repairing machine capable of functioning for tens of thousands of years at the minimum. People are happy if their cars last 200k miles. People like to talk up how amazing Earth is for life. Look up hypothetical “super habitable worlds.” Earth may be kinda crappy in actuality. [Previous page](https://boards.straightdope.com/t/how-many-planets-in-our-galaxy-harbor-intelligent-life/726578.md?page=3)