<p>I think that your question makes flawed assumptions.</p>
<p>One) That every planet that has life must have intelligent life who count as people.</p>
<p>Two) That every planet that has intelligent life must have only one species of intelligent life who count as people.</p>
<p>The planet Earth proves that both assumptions are inaccurate.</p>
<p>One) Earth was occupied by only single celled life and viruses for billions of years.  Eventually photosynthetic single celled organisms produced oxygen faster than oxidation could remove it from the atmosphere, and lifeforms evolved to tolerate oxygen and to use it.  Oxygen using lifeforms developed multicellular organisms.</p>
<p>Assuming that single celled organisms couldn't possible be intelligent beings, and that many multicelled organisms likeplants and sponges couldn't possibly be intelligent beings, the first possibility of multicelled lifeforms advanced enough to be intelligent beings would have been about maybe 600 million years ago.</p>
<p>So Earth probably had lifeforms for billions of years before lifeforms which could possibly develop intelligence evolved.</p>
<p>By looking at a planet from afar and measuring its conditions with various instruments we can tell if the planet can possibly have intelligent life as we know it at the moment, not whether it does have intelligent life as we know it at the moment.</p>
<p>And an advanced technological civilization may cause environmental changes which can be detected at a distance.  But advanced technological civilization has existed on Earth for only a few hundred or a few thousand years, while there have been intelligent beings of the genus <em>Homo</em> on Earth for hundeds of thousands or millions of years. Human civilization might exist for hundreds of thousands or millions of years in the future, but that would not change the hundreds of thousand or millions of years that intelligent life existed on Earth without making any signs which could be detected at a distance.</p>
<p>Two) The history of Earth shows that it is possible for a planet to have more than one species of intelligent life living on it at the same time.</p>
<p><em>Homo sapiens</em> evolved about 300,000 yeas ago.</p>
<p><em>Homo floresiensis</em> existed on Flores hundreds of thousands of years before becoming extic 60,000  or 50,000 years ago.</p>
<p>The Denisovan species or subspecies may have existed over 200,000 years ago and as recently as 50,000 years ago.</p>
<p><em>Homo neanderthalenis</em> may have existed more than 400,000 yeas ago and became extinct about 40,000 years ago.</p>
<p><em>Homo erectus</em> existed from about 2,000,000 years ago to about 100,000 years ago.</p>
<p><em>Homo habilis</em> existed from about 2,310,000 years ago to about 1,650,000 years ago.</p>
<p>Members of various species in the genus <em>Australopithicus</em> existed from about 4,200,000 years ago to about 1,900,000 years ago or later.  And members of <em>Australopithicus</em> may be considered by many persons to have been intelligent beings.</p>
<p>Most of the  thousands of mammal species are small.  There are hundreds of large mammals, large enough to suport large brains.  And some of those large mammal species have evolved large brains for various reasons.  And mammals with large brains may develop high intelligence, including intelligence ranges which greatly overlap with those of humans.</p>
<p>Two species of chimps and two species of gorillas may be intelligent enough to count as intelligent beings.  Maybe the three species of orangutans and the 20 species of gibbons are also intelligent enough to count as intelligent beings.</p>
<p>The three species of elephants also may be intelligent enough to count as intelligent beings.  And over fifteen species, if I counted correctly, of large brained proposcideans related more or less closely to modern elephants became extinct during the last 13,000 years or so.  Fossil proboscideans with large brains have existed for at least 10 million years.</p>
<blockquote>
<p>Cetacea is an infraorder that comprises the 94 species of whales, dolphins, and porpoises.</p>
</blockquote>
<p><a href="https://en.wikipedia.org/wiki/List_of_cetaceans" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/List_of_cetaceans</a></p>
<p>All cetacean species have large brains and many have been observed exhibiting high intelligence.  Nobody can be certain whether none, some, or all, cetacean species should be considered to be intelligent beings.  Large brained cetaceans have existed for at least 10 million years.</p>
<p>Thus it is possible that the planet Earth currently has between one and over one hundred species of intelligent mammals.  And it possible that Earth has had at least two species of intelligent mammals at a time for over ten milions years and possibly much longer.</p>
<p>Most flying birds are quite small, and thus they have small brains.  But bird brains seem to have evolved high efficiency in order to have sufficient functionality for survival in such small brains.</p>
<p>So some species of birds, such as parrots and corvids, seem to display high intelligence approachign that of humans, despite their entire bodies being not much heavier than human brains.  Thus the idea of past, present, or future intelligent species of birds is fairly reasonable.</p>
<p>If other groups of flying creatures also develop highly efficent brains, it is possible that they may have developed human levels of intelligence.</p>
<p>I also note that some extinct flying creatures have had body masses equal to or greater than an average human.  Thus it is theoretically possible for a flying being to have a brain as large as human brain.</p>
<blockquote>
<p>Argentavis magnificens was among the largest flying birds ever to exist</p>
</blockquote>
<p>The mass is estimated to be about 72 to 74 kilograms or 154 to 159 pounds.</p>
<p><a href="https://en.wikipedia.org/wiki/Argentavis" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/Argentavis</a></p>
<p>The largest extinct flying reptiles were even larger.</p>
<blockquote>
<p>Quetzalcoatlus /kɛtsəlkoʊˈætləs/ is a genus of pterosaur known from the Late Cretaceous period of North America (Maastrichtian stage); its members were among the largest known flying animals of all time.</p>
<p>Body mass estimates for giant azhdarchids are extremely problematic because no existing species share a similar size or body plan, and in consequence, published results vary widely.<a href="https://en.wikipedia.org/wiki/Quetzalcoatlus#Size" rel="nofollow noreferrer">3</a> Generalized weight, based on some studies that have historically found extremely low weight estimates for Quetzalcoatlus, was as low as 70 kg (150 lb) for a 10 m (32 ft 10 in) individual. A majority of estimates published since the 2000s have been substantially higher, around 200–250 kg (440–550 lb).[12][13]</p>
</blockquote>
<p><a href="https://en.wikipedia.org/wiki/Quetzalcoatlus#Size" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/Quetzalcoatlus#Size</a></p>
<p>So it is theoretically possible for a flying animal to have a brain large enough for intelligence, even if a brain the size of a human brain is necessary for intelligence.</p>
<p>Some cephalopods, like octopuses, display high intelligence, and thus it may be possible for some cephalopods to be intelligent beings.</p>
<p>I once read that hundreds of thousands or even over a million giant squid might be eaten every day by predators.  So I certainly hope that giant squid are not intelligent.</p>
<p>You might have heard the song &quot;Octopus's Garden&quot;.  There is a theory, which is not widely accepted, that a fossel of a prehistoric cephalopod's garden under the sea has been found.</p>
<p>In 2011 it was suggested that the vertibrae of ichthyosaurs found in a strange double line might have been arranged by some really gigantic cephalopod which had killed them.  Which suggests a highy inteligent giant cephalopod playing with the bones of its food and possibly arranging them to look like the double row of suckers on a tenticle.</p>
<p><a href="https://www.nature.com/articles/news.2011.586" rel="nofollow noreferrer">https://www.nature.com/articles/news.2011.586</a></p>
<p>So possibly there was a species of intelligent giant cephalopods in Earth's oceans 228 million years ago.</p>
<p>So it is possible that there have been many species of inteligent beings on Earth, on and off over hundreds of millions of years, with several different major body plans and many more minor variations on each body plan.</p>
<p>So it seems impossible to predict the appearance of intelligent beings on Earth from the environmental condiitons on Earth.</p>
<p>And the same difficulty in predicting the appearance of intelligent life may go for other planets with life.</p>

CC BY-SA 4.0
2022-12-21T05:47:40.427Z
That’s a great answer. Unfortunately I initially was not precise enough on my initial question. I was asking about intelligent life with a technology compared from humans of the 1950s. And I doubt the life in your answer was able to create such technology.
Daniel
CC BY-SA 4.0
2022-12-23T07:16:56.470Z
@Daniel  Great Apes have anatomy quite similar to humans, and of course other members of genus Homo were even more like members of Homo sapiens.  Elephant trunks give them consideable manipulative ability, and roughly  elephant shaped aliens with high technology have been imagined, for example in Invaders from Rigel by Fletecher Pratt and Footfall by Larry Niven and Jerry Pournelle.  As land animals, they could discover fire and metallurgy.  That would be a problem for water dwelling cetaceans (who also lack arms) & cephalopods.  Continued.
M. A. Golding
CC BY-SA 4.0
2022-12-23T07:24:09.823Z
@Daniel And if advanced aliens visit a planet and find that it has intelligent water dwelling aliens shaped like cetaceans or cephalopods, it might make bionic arms for them and give technology for underwater metallugury and/or spacesuit equivalents to walkand work on dry land -and give them civilization.  See for example the Larry Niven story "Handicapped" https://archive.org/details/Galaxy_v26n02_1967-12_modified/page/n79/mode/2up?view=theater
M. A. Golding
CC BY-SA 4.0
2022-12-20T18:09:12.253Z
2022-12-20T18:15:26.690Z
2022-12-20T18:15:26.690Z
M. A. Golding
<p>I wonder if one can estimate the body-shape of intelligent life (comparable to humans) living on land just by taking into account the physical conditions of the planet. With intelligent life (comparable to humans) I mean human like life whose technology is at least as advanced as human technology in the 1950s. Let us assume there is at maximum one species on the planet meeting above conditions. By shape I mean e.g.</p>
<ul>
<li>the average size</li>
<li>number of arms (are there even arms needed)</li>
<li>number of fingers</li>
<li>size-ratio of head to body (if there is even something like a head)</li>
<li>where is the head</li>
<li>is the brain in the head</li>
<li>...</li>
</ul>
<p>To clarify this question, I would like to have an answer which addresses both points:</p>
<p>1.) What conditions on the body have to be <strong>generally</strong> satisfied for intelligent life?</p>
<p>No matter how clever you are, a intelligent species needs to have the physical conditions to evolve. For humans to evolve and build tools it was mandatory that we have thumbs. If there were only four fingers without a thumb, I hardly believe we could build any tools and would not have been evolved.</p>
<p>2.) What conditions on the body have to be <strong>specially</strong> (= based on the physical conditions of the certain planet) satisfied for intelligent life?</p>
<p>I guess on earth it would be unlikely that an important part like the head could be close to the ground as it is a very important part, and it wouldn't be too good if it was put in danger to always knock against any obstacle. Furthermore, the ratio of height compared to gravitational forces should be an important factor as if we would be too tall, we would have an increased risk of dying by hitting the ground with our head to heavy.</p>
<p><strong>Edit 1</strong>: I edited the question to better clarify what kind of life I mean. I am talking about life whose technology is at least the as advanced as our technology from around 1950s. This clarification is important because I think it is pretty important to have a certain body shape to be able to do construction. You could be the cleverest person on earth, if you don't have arms and legs, you cannot start constructing anything.</p>

CC BY-SA 4.0
2022-12-20T13:18:49.273Z
Welcome! Given the huge variation in body shapes and sizes on earth, one would imagine that an alien species would have no clue about us. Why quadrilateral, symmetrical, notochords did so well seems half chance and half because it is of good utility, although even that may just be our bias and lack of imagination. We can likely _guess_ the upper limit of size... Although even that is based on our limited imagination of life. So I'd say the answer is no, but I do like the way you think
Rabbi Kaii
CC BY-SA 4.0
2022-12-20T18:40:43.987Z
1.) Have you researched into other intelligent life on this planet? 2.) Have you researched into what weird looking stuff died out on this planet just a few 10-thousand years ago, that you have never seen before? Once you do 1. and 2. you will probably conclude that nature is more inventive than what we can ever imagine, and hence speculating about exobiology is doomed to fail.
AtmosphericPrisonEscape
CC BY-SA 4.0
2022-12-20T21:12:24.793Z
@AtmosphericPrisonEscapen Sorry I was not precise about 1 and 2. I am talking about a species whose technology is at least as advanced as human-technology in the 1950s. And to achieve this you need a certain shape. No arms/fingers means no technology. Even a hand without a thumb would be mostly useless.
Daniel
CC BY-SA 4.0
2022-12-20T22:24:27.467Z
Why would it? What about an octopus?
planetmaker
CC BY-SA 4.0
2022-12-21T05:44:10.290Z
@planetmaker question is about Land living, octopus lives in water. And I guess there is a reason why octopus is not living on land due to physical conditions of the planet earth.
Daniel
CC BY-SA 4.0
2022-12-21T05:46:42.873Z
Be creative, think of octopus having evolved to live on land, walking on two or four of their feet, leaving them with 4 or 6 feet to manipulate things. It is an alien world. Who knows how evolution worked there
planetmaker
CC BY-SA 4.0
2022-12-21T05:55:22.790Z
I can imagine that. And an octopus has arms (some call them tentacles). Would you agree that intelligent life would not be possible without arms/tentacles?
Daniel
CC BY-SA 4.0
2022-12-23T16:30:33.737Z
Daniel - I would disagree with that. We have such a small sample size (1 planet, with everything descended from one source) that we cannot make any assumptions about intelligent life anywhere
Rory Alsop
CC BY-SA 4.0
2022-12-23T16:32:14.567Z
I would suggest looking at our Worldbuilding sister site - you may be able to edit this question to fit there.
Rory Alsop
<life>
Is it possible to estimate the body-shape of intelligent life just by taking into account the physical conditions of a planet?
Daniel
# Is it possible to estimate the body-shape of intelligent life just by taking into account the physical conditions of a planet?

(Asked by: username_0 on 2022-12-20)

I wonder if one can estimate the body-shape of intelligent life (comparable to humans) living on land just by taking into account the physical conditions of the planet. With intelligent life (comparable to humans) I mean human like life whose technology is at least as advanced as human technology in the 1950s. Let us assume there is at maximum one species on the planet meeting above conditions. By shape I mean e.g.

* the average size
* number of arms (are there even arms needed)
* number of fingers
* size-ratio of head to body (if there is even something like a head)
* where is the head
* is the brain in the head
* ...

To clarify this question, I would like to have an answer which addresses both points:

1.) What conditions on the body have to be **generally** satisfied for intelligent life?

No matter how clever you are, a intelligent species needs to have the physical conditions to evolve. For humans to evolve and build tools it was mandatory that we have thumbs. If there were only four fingers without a thumb, I hardly believe we could build any tools and would not have been evolved.

2.) What conditions on the body have to be **specially** (= based on the physical conditions of the certain planet) satisfied for intelligent life?

I guess on earth it would be unlikely that an important part like the head could be close to the ground as it is a very important part, and it wouldn't be too good if it was put in danger to always knock against any obstacle. Furthermore, the ratio of height compared to gravitational forces should be an important factor as if we would be too tall, we would have an increased risk of dying by hitting the ground with our head to heavy.

**Edit 1**: I edited the question to better clarify what kind of life I mean. I am talking about life whose technology is at least the as advanced as our technology from around 1950s. This clarification is important because I think it is pretty important to have a certain body shape to be able to do construction. You could be the cleverest person on earth, if you don't have arms and legs, you cannot start constructing anything.

**Tags:** life

> **Comments:**
> **username_1**: Welcome! Given the huge variation in body shapes and sizes on earth, one would imagine that an alien species would have no clue about us. Why quadrilateral, symmetrical, notochords did so well seems half chance and half because it is of good utility, although even that may just be our bias and lack of imagination. We can likely _guess_ the upper limit of size... Although even that is based on our limited imagination of life. So I'd say the answer is no, but I do like the way you think  
> **username_2**: 1.) Have you researched into other intelligent life on this planet? 2.) Have you researched into what weird looking stuff died out on this planet just a few 10-thousand years ago, that you have never seen before? Once you do 1. and 2. you will probably conclude that nature is more inventive than what we can ever imagine, and hence speculating about exobiology is doomed to fail.  
> **username_0**: @AtmosphericPrisonEscapen Sorry I was not precise about 1 and 2. I am talking about a species whose technology is at least as advanced as human-technology in the 1950s. And to achieve this you need a certain shape. No arms/fingers means no technology. Even a hand without a thumb would be mostly useless.  
> **username_3**: Why would it? What about an octopus?  
> **username_0**: @username_3 question is about Land living, octopus lives in water. And I guess there is a reason why octopus is not living on land due to physical conditions of the planet earth.  
> **username_3**: Be creative, think of octopus having evolved to live on land, walking on two or four of their feet, leaving them with 4 or 6 feet to manipulate things. It is an alien world. Who knows how evolution worked there  
> **username_0**: I can imagine that. And an octopus has arms (some call them tentacles). Would you agree that intelligent life would not be possible without arms/tentacles?  
> **username_4**: username_0 - I would disagree with that. We have such a small sample size (1 planet, with everything descended from one source) that we cannot make any assumptions about intelligent life anywhere  
> **username_4**: I would suggest looking at our Worldbuilding sister site - you may be able to edit this question to fit there.  

---

## 1 answers

### Answer by username_5 on 2022-12-20. Score: 4

I think that your question makes flawed assumptions.

One) That every planet that has life must have intelligent life who count as people.

Two) That every planet that has intelligent life must have only one species of intelligent life who count as people.

The planet Earth proves that both assumptions are inaccurate.

One) Earth was occupied by only single celled life and viruses for billions of years. Eventually photosynthetic single celled organisms produced oxygen faster than oxidation could remove it from the atmosphere, and lifeforms evolved to tolerate oxygen and to use it. Oxygen using lifeforms developed multicellular organisms.

Assuming that single celled organisms couldn't possible be intelligent beings, and that many multicelled organisms likeplants and sponges couldn't possibly be intelligent beings, the first possibility of multicelled lifeforms advanced enough to be intelligent beings would have been about maybe 600 million years ago.

So Earth probably had lifeforms for billions of years before lifeforms which could possibly develop intelligence evolved.

By looking at a planet from afar and measuring its conditions with various instruments we can tell if the planet can possibly have intelligent life as we know it at the moment, not whether it does have intelligent life as we know it at the moment.

And an advanced technological civilization may cause environmental changes which can be detected at a distance. But advanced technological civilization has existed on Earth for only a few hundred or a few thousand years, while there have been intelligent beings of the genus *Homo* on Earth for hundeds of thousands or millions of years. Human civilization might exist for hundreds of thousands or millions of years in the future, but that would not change the hundreds of thousand or millions of years that intelligent life existed on Earth without making any signs which could be detected at a distance.

Two) The history of Earth shows that it is possible for a planet to have more than one species of intelligent life living on it at the same time.

*Homo sapiens* evolved about 300,000 yeas ago.

*Homo floresiensis* existed on Flores hundreds of thousands of years before becoming extic 60,000 or 50,000 years ago.

The Denisovan species or subspecies may have existed over 200,000 years ago and as recently as 50,000 years ago.

*Homo neanderthalenis* may have existed more than 400,000 yeas ago and became extinct about 40,000 years ago.

*Homo erectus* existed from about 2,000,000 years ago to about 100,000 years ago.

*Homo habilis* existed from about 2,310,000 years ago to about 1,650,000 years ago.

Members of various species in the genus *Australopithicus* existed from about 4,200,000 years ago to about 1,900,000 years ago or later. And members of *Australopithicus* may be considered by many persons to have been intelligent beings.

Most of the thousands of mammal species are small. There are hundreds of large mammals, large enough to suport large brains. And some of those large mammal species have evolved large brains for various reasons. And mammals with large brains may develop high intelligence, including intelligence ranges which greatly overlap with those of humans.

Two species of chimps and two species of gorillas may be intelligent enough to count as intelligent beings. Maybe the three species of orangutans and the 20 species of gibbons are also intelligent enough to count as intelligent beings.

The three species of elephants also may be intelligent enough to count as intelligent beings. And over fifteen species, if I counted correctly, of large brained proposcideans related more or less closely to modern elephants became extinct during the last 13,000 years or so. Fossil proboscideans with large brains have existed for at least 10 million years.

> Cetacea is an infraorder that comprises the 94 species of whales, dolphins, and porpoises.

<https://en.wikipedia.org/wiki/List_of_cetaceans>

All cetacean species have large brains and many have been observed exhibiting high intelligence. Nobody can be certain whether none, some, or all, cetacean species should be considered to be intelligent beings. Large brained cetaceans have existed for at least 10 million years.

Thus it is possible that the planet Earth currently has between one and over one hundred species of intelligent mammals. And it possible that Earth has had at least two species of intelligent mammals at a time for over ten milions years and possibly much longer.

Most flying birds are quite small, and thus they have small brains. But bird brains seem to have evolved high efficiency in order to have sufficient functionality for survival in such small brains.

So some species of birds, such as parrots and corvids, seem to display high intelligence approachign that of humans, despite their entire bodies being not much heavier than human brains. Thus the idea of past, present, or future intelligent species of birds is fairly reasonable.

If other groups of flying creatures also develop highly efficent brains, it is possible that they may have developed human levels of intelligence.

I also note that some extinct flying creatures have had body masses equal to or greater than an average human. Thus it is theoretically possible for a flying being to have a brain as large as human brain.

> Argentavis magnificens was among the largest flying birds ever to exist

The mass is estimated to be about 72 to 74 kilograms or 154 to 159 pounds.

<https://en.wikipedia.org/wiki/Argentavis>

The largest extinct flying reptiles were even larger.

> Quetzalcoatlus /kɛtsəlkoʊˈætləs/ is a genus of pterosaur known from the Late Cretaceous period of North America (Maastrichtian stage); its members were among the largest known flying animals of all time.
>
> Body mass estimates for giant azhdarchids are extremely problematic because no existing species share a similar size or body plan, and in consequence, published results vary widely.[3](https://en.wikipedia.org/wiki/Quetzalcoatlus#Size) Generalized weight, based on some studies that have historically found extremely low weight estimates for Quetzalcoatlus, was as low as 70 kg (150 lb) for a 10 m (32 ft 10 in) individual. A majority of estimates published since the 2000s have been substantially higher, around 200–250 kg (440–550 lb).[12][13]

<https://en.wikipedia.org/wiki/Quetzalcoatlus#Size>

So it is theoretically possible for a flying animal to have a brain large enough for intelligence, even if a brain the size of a human brain is necessary for intelligence.

Some cephalopods, like octopuses, display high intelligence, and thus it may be possible for some cephalopods to be intelligent beings.

I once read that hundreds of thousands or even over a million giant squid might be eaten every day by predators. So I certainly hope that giant squid are not intelligent.

You might have heard the song "Octopus's Garden". There is a theory, which is not widely accepted, that a fossel of a prehistoric cephalopod's garden under the sea has been found.

In 2011 it was suggested that the vertibrae of ichthyosaurs found in a strange double line might have been arranged by some really gigantic cephalopod which had killed them. Which suggests a highy inteligent giant cephalopod playing with the bones of its food and possibly arranging them to look like the double row of suckers on a tenticle.

<https://www.nature.com/articles/news.2011.586>

So possibly there was a species of intelligent giant cephalopods in Earth's oceans 228 million years ago.

So it is possible that there have been many species of inteligent beings on Earth, on and off over hundreds of millions of years, with several different major body plans and many more minor variations on each body plan.

So it seems impossible to predict the appearance of intelligent beings on Earth from the environmental condiitons on Earth.

And the same difficulty in predicting the appearance of intelligent life may go for other planets with life.

> **Comments:**
> **username_0**: That’s a great answer. Unfortunately I initially was not precise enough on my initial question. I was asking about intelligent life with a technology compared from humans of the 1950s. And I doubt the life in your answer was able to create such technology.  
> **username_5**: @username_0  Great Apes have anatomy quite similar to humans, and of course other members of genus Homo were even more like members of Homo sapiens.  Elephant trunks give them consideable manipulative ability, and roughly  elephant shaped aliens with high technology have been imagined, for example in Invaders from Rigel by Fletecher Pratt and Footfall by Larry Niven and Jerry Pournelle.  As land animals, they could discover fire and metallurgy.  That would be a problem for water dwelling cetaceans (who also lack arms) & cephalopods.  Continued.  
> **username_5**: @username_0 And if advanced aliens visit a planet and find that it has intelligent water dwelling aliens shaped like cetaceans or cephalopods, it might make bionic arms for them and give technology for underwater metallugury and/or spacesuit equivalents to walkand work on dry land -and give them civilization.  See for example the Larry Niven story "Handicapped" https://archive.org/details/Galaxy_v26n02_1967-12_modified/page/n79/mode/2up?view=theater  

---

