There was a time when I felt that classic sci-fi like Star Trek, the original series and The Next Generation were ridiculous in assuming so many humanoid life forms in the universe. In the 1960s, we did not even know if there WERE any other suns with planets around them, let alone earth-like planets.
While I did not discard the possibility of extraterrestrial life per se, I felt it was absurd to think that intelligent life elsewhere, following a different evolutionary path, would look anything like a human being. I felt that ETs like Worf or Mr. Spock, who were really homo sapiens with bumpy heads and funny ears, were just an attempt to give us characters we could relate to.
But now, looking at modern discoveries in astronomy, astrophysics and biology, I am starting to think that intelligent humanoid ETs could be much more likely than I had supposed.
I am not a scientist. I am a science buff and here, in no particular order, are reasons I think anthropomorphic ETs are possible and perhaps probable.
We have just found out (past few decades) with space telescopes that there must be hundreds of billions of suns with planets, and yes, billions of earth-like planets in the Goldilocks zone where liquid water can exist.
It turns out water is incredibly common in the universe, in interstellar clouds, even on the Moon. So if water is necessary for life, no problem there!
Life appeared on Earth so soon after it cooled down that scientists believe that comets may have “seeded” our planet with the building blocks of life. So they must have seeded other planets. So life in the universe may be “related” to all other life, despite being separated by so many light-years.
4)Even if life forms evolve on different planets, certain laws of physics and simple common sense tell us that intelligent beings would fall in a certain size range, for example. It would be impossible for a mouse to have a human-like brain, and for many reasons neither can a large creature like an elephant or a dinosaur. Similarly, they would probably have binocular vision, be bilaterally symmetrical, have hearing etc.
It appears there is not an infinite number of ways a creature can evolve. Physical laws direct evolution along certain pathways. For example, large cats developed sabre teeth on three or four INDEPENDENT occasions. Similarly, look at how marsupial mammals developed. At one point there was a marsupial lion, a marsupial wolf, a marsupial “bear”. As if evolution just had to “cast” animals in certain roles. What if there had been a marsupial ape? Might it have developed into a marsupial human?
Being intelligent and creative without being able to manipulate things with your fingers and arms is useless. Such a creature could never develop human-like intelligence because he or she could not do anything with it. So using a couple of limbs for locomotion and some for manipulating the environment seem to be a sine qua non of intelligent life. In other words, I doubt if intelligent ETs would ever be on all fours (or sixes or eights).
Sure, calcium phosphate bones, with muscles to move 'em, and a fast metabolism, are all really inviting. It works crackers for us, so why not elsewhere?
But there really are alternatives. Aliens might have tentacles that work by internal fluid pressure; this is a perfectly valid functionality for extremities.
(To be vulgar, it works well for mammalian males…)
Just look at how many different paths evolution has taken right here on Earth. Yes, alien people would have to have manipulative organs. Maybe those are forelimbs, and the creature has adapted to walking on hind limbs as a result. Maybe the creature has thumbs on all of its limbs, and uses any of them for locomotion or grasping interchangeably, like a monkey. Maybe, also like a monkey, it has a prehensile tail. Maybe it has tentacles like an octopus. Heck, we’ve got a creature right here on Earth with a prehensile nose, of all things. If the Universe really allows for a creature with a prehensile nose, I’m not prepared to rule out much of any possible body plan.
Well, imagine the physiology of a centaur. If six limbs were normal for a given planet’s vertebrate-analogues, it is possible a great many species would evolve in such a way as to use their forelimbs for manipulation rather than locomotion.
Well, if all we’re talking about is the basic building blocks, that does not mean “related” in a genetic or chromosomal sense, it just means other planets’ life-forms (that is, those resulting from comet-seeding, which would not necessarily be the case on all life-bearing planets) would be based on amino acids similar to Earth life-forms.
Actually, I do not know why an elephant could not have a human-like brain. Their brains are certainly big enough – perhaps not as big as ours proportional to the whole body mass, but evolution could take care of that with a bit of reinforcement to the muscles and bones of the neck.
No not really, they are imperceptibly more likely over time as evolution continues elsewhere perhaps, but their likelihood hasn’t changed, only our perception of the possibility of humanoid aliens is changing.
I’ll side with those who say that we don’t have enough information to make a judgment about the likely form of extraterrestrials. On one hand we only have information about life on one single planet; on the other hand, the variety of life forms here is absolutely staggering.
One of the interesting speculations even on this planet is what might have happened if the dinosaurs had not gone extinct, which appears to have been due to a one-time anomalous event. It’s been speculated that they might have become the dominant intelligent species. I once had a book on dinosaurs with an imaginative picture that I wish I could find again, showing an evolved dinosaur-like creature with an expressive, intelligent, almost human-like face. That could have been the path of evolution.
More likely than what? As far as I know we have exactly zero examples of extraterrestrial life, whether intelligent or not. The Wow! radio message is about as good as it gets, again afaik. However, in an infinite universe (or at least a really, really big one) then I suppose the chances of another bi-pedal bilaterally symmetric humanoid creature similar to us is possible…though we might be the one example in the universe I suppose. But I don’t think this is more or less likely than it was a decade ago, and really we won’t know until and unless we start exploring more of our own neck of the woods, not to mention the rest of the galaxy and universe (if we ever do).
On Cosmos I recall Neil DeGrasse Tyson talking about how there may be a certain area of the galaxy where life seeding is more likely, and that when planets pass through it they could increase their chances of having life develop.
Well I think what the OP means, to be fair, is do we have recent evidence that intelligent extraterrestrials would necessarily be constrained to human-like forms. Which is a reasonable question, but I think the answer is “no, we don’t”. And until some reasonable sample of such ETs may be identified – which may be never (not because they’re not out there, but because of the distances involved) – it would be pure speculation. Indeed it’s entirely possible that humanity itself may, in a remarkably short timeframe relative to biological evolution, transcend the biological human form through bioengineering and man-machine hybridization.
There is just one reason to believe that if there are intelligent extra-terrestrials they will be humanoid. It’s because we only know of one form of intelligent life that has worked. Considering the enormous number of possibilities I don’t find that to be a very convincing reason.
I wasn’t clear – yes, there have been multiple mass extinctions. I meant anomalous one-time event as in the asteroid impact which is believed to have been the cause of the dinosaurs’ extinction, as opposed to a natural climate change or evolutionary adaptations by competitive species.
That’s the idea, though that wasn’t the picture. The picture that I recall was a lot more human-like-- you could just see the intelligence in the eyes, yet it was still reptilian – a very haunting hybrid!
Well, we don’t really know what caused all the mass extinctions, although super-volcanoes could have been one cause. I wouldn’t put that in the category of climate change. In fact, there is some debate even today what the cause of the dinosaur extinction was.
Just google “if dinosaurs had evolved intelligence” and look at images. I think you’ll find the one you’re looking for.
I just don’t think it’s in any way requisite. Instead of arms, for instance, an alien life-form might have some sort of arm-like appendages that grow out of specialized ribs. The function might be similar, but the pathway is completely different.
Others have already addressed the general points that we don’t have enough cohorts to make an estimate of variability of forms intelligent life may take, the potential variation in evolutionary paths, but these particular assumptions bear a more detailed discussion, insofar as they being with the implicit presupposition that the hominid form and size is most likely (i.e. superior) and other forms would be suboptimal. However, this is an essentially ontological approach, and we we can only assess it in terms of our particular evolutionary history and the environment in which we have evolved. In other words, even if it were true, it would only apply to other intelligent beings who evolved in a similar physical environment and exposed to similar selective pressures.
Even given this assumption, can see from examining other generally acknowledged highly intelligent species who could, without competition from us, eventually achieve sentience and develop technology that there are a wide variety of physical forms, sizes, manipulative appendages, and brain sizes. From cetaceans (bottlenose dolphins and humpback whales) to cephalopods (octopus and squid) to covids (crows and ravens) intelligence spans a wide array of forms and functionality. There is no reason to believe that intelligence in other environments wouldn’t develop in equally broad variety, and that any one form might, given different selective pressures, develop more than another.
Although bilateral symmetry is appealing to us and makes a certain degree of motor sense for marine creatures which propel themselves using body/caudal fin and median/paired fin propulsion (and similarly for insects), but it is hardly a requisite precursor to locomotion in general and the general bilateral symmetry of virtually all reptiles, aves, and mammals can be essentially tied to the accident of evolution that all of these were derived from the lobed fishes that first ventured out of the ocean. We can only assume this to be true of alien life that formed along a similar path, which is by no means certain.
The last argument, that manipulative digits similar to arms and fingers are needed for a species to attain sentience and industry, while somewhat more generalized, still requires a very constrained view of intelligence or technology. While we regard the use of natural items such as clubs and rocks as part of our essential evolution from tool users to tool makers, an alien species may take another tack; say, using biochemical control to extrude carbonaceous, calcium, or magnesium structures and tools (particularly if the species is aquatic). A different evolutionary path could still lead to tool use, energy production and regulation, the development of protective artificial environments, and extension of mechanical and intellectual capabilities that would be in every way equal in accomplishment to human industrial society.
It is true that there are hundreds of billions of star systems in our galaxy, and hundreds of billions of galaxies in the observable universe. The conditions for life as we would recognize it may exist in only a small fraction of these (although our assumption of suitable conditions may need to be expanded to include seemingly arid or frigidly cold environments) but that still leaves a significant total number (likely in the hundreds of thousands or millions) in our galaxy alone. However, the conditions for an Earth-like world and particular evolutionary history, e.g. a large moon, rakish axial tilt, dominant single mass to help clear the star system of debris, et cetera, will place a significant limitation on assuming any particular evolutionary history similar to the development of life on Earth, and as noted by others, even life on Earth has adopted wildly varying forms, in which one member of one particular subbranch of one order in a large class have come to dominate as a tool user.
It is possible that some bipedal or even vaguely humanoid form of intelligent life could develop elsewhere, but the odds it would look as similar to a hominid as, say, a Kree or a Klingon (much less be able to interbreed as these apparently can) is so vanishingly remote as to be essentially impossible, and that this is a common trope in science fiction is purely a convenience to authors and filmmakers who want an ‘alien’ species that the audience can relate to and doesn’t cost a fortune to render on screen. Real alien life could be as different from humanity as a slime mold or nematode, or indeed, not made out of amino acids at all and perhaps totally incomprehensible or even unrecognizable.
We really can’t say much definitive about alien life except that it is virtually certain to be substantially unlike anything we are familiar with on Earth, and possibly more different than the wildest dreams of fanciful science fiction writers.
Ahh, no. The “building blocks” being speculated about here are not genetic material. They are, at best, amino acids and lipids. From such a basic starting point, you aren’t going to get multiple organisms that use DNA, much less organisms that are in any way related.
Of course, even if we were to seed planet with actual bacteria that are related to us, there is no reason to assume they would even evolve into vertebrates, much less into anything resembling us.
The lower size limit may be correct for terrestrial mammals. The upper size limit, no. There is no reason at all why an elephant or a whale can’t have a human-like brain.
You are assuming that the processors of these animals are in any way similar to our own. That would be incredibly unlikely. Our own brains are the result of a series of frozen accidents. they aren’t even very sensible, much less efficient. For example, we have neurons that use energy to *not *transmit information, and send information by default when they run out of energy. That’s just plain dumb, and the result of the way that they evolved from motile fibres in unicellular organisms. It would be staggeringly unlikely that evolved independently wouldn’t use any analogous system. If ET life used nanotubule conductors or haematite wiring, then the functional constraints of their brains would be so different from ours that we can;t even begin to speculate on size.
Bilateral symmetry is likely, but not essential. The fact that manifold symmetry has re-evolved so many times from bilateral symmetry would make me reticent to say that it’s inevitable.
Binocular vision, no. There’s just no basis for this. We have binocular vision because we evolved from creatures whose larvae had two eyes. That’s it. Plenty of other creatures on Earth have any other number of eyes and they function just fine in every conceivable niche.
Hearing, almost certainly not in any form that you would recognise as hearing. Ability to detect vibration, sure. Doing so through holes it he skull that vibrate the jawbones? Not a chance. That’s another series of frozen and not very effective accidents. Detecting vibrations through our knees, or through our genitals that rest on the ground or from the hairs in pits along our midline. Sure other species detect vibration that way. But hearing as you understand it or that produces analogous sensory input? Not a chance.
It appears there is not an infinite number of ways a creature can evolve.
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As close to infinite as makes no difference.
Not in any sense.
Because their ancestors all started out with enlarged caninesand that trait became magnified. Now, look at the marsupial lion. Its ancestor didn’t have enlarged, so it developed sabre teeth fro enlarged incisors.
And of course of the ancestor doesn’t have teeth at all, then the organism will develop stabbing organs from it lips.
And if the organism doesn’t even have lips, then it will develop a stabbing organ form its tentacles.
This is the point that so many people overlook. If you start from a common form, then there are a limited number of solutions if you want to evolve wings, or stabbing tools.
But when you start from completely different form, you can evolve stabbing weapons from lips or tentacles and you can evolve wings from gills or genitals. there are an infinite number of ways to produce a solution from different starting points. The constraints are not physical, they are due to ancestry.
There was never a marsupial that filled the niche of a bear. And there was never a marsupial hippopotamus, or marsupial buffalo or marsupial bat. And conversely there is no placental kangaroo, placental wombat or placental bandicoot.
You have found a few examples of where animals that are closely related evolved vaguely similar solutions (though with major differences in the way they solved those problems as noted above. But you have overlooked the many more examples where no parrallells ever evolved between the groups.
And of course if you look at less related organisms, you notice that there is no similarity at all. While we have reptilian grazers and predators and so forth, why is there no reptilian lion, reptilian wolf, or reptilian bear? Why is there no mammalian squid, or mammalian robber crab? Why is that if evolution just had to “cast” animals in certain role? If there is this pressure for casting, why did vertebrates settle on a totally different design for coconut eaters and marine predators? Why didn’t a tortoise ever evolve into a robber crab, or a porpoise ever evolve into a squid? Because when you start with a slater or a chiton, you are never going to end up with a monkey or a porpoise, but you might end with a robber crab or a squid, which are radically different inform and function but solve the same problems.
There were plenty of primate apes, and only one of the evolved into a primate human. So the answer is “probably not”.
Only if you define arm as “something humans have”. So using a couple of limbs for locomotion and some for manipulating the environment seem to be a sine qua non of intelligent life.
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Squid and elephants have no problem manipulating objects despite lacking arms or fingers. And the squid evolved from an ancestor with just a single fleshy foot that much later developed into grasping tentacles. Which goes to show how radically different solutions can be if you start from a radically different starting point.
Why not? Mantis or crab type life-forms that have adapted the first of multiple leg pairs into dedicated grasping organs have evolved independently at least 12 times. In contrast, only one vertebrate has made this transition. The only other vertebrates that have dedicated grasping organs are the elephants, and they are four footed and use their nose to grasp. So 16 to 1, grasping organs evolve in multi-legged animals.
That would suggest that it is orders of magnitude more likely that intelligent ETs would be on all fours (or sixes or eights).
A few scientists, such as Milton Wainwright and Chandra Wickramasinghe, think that DNA itself is being vectored between the planets. I’m pretty sure they are wrong, except in very localised situations. Perhaps transfer of living material containing DNA might occur within a solar system, or a newly-formed star cluster (a newly-formed cluster might be the ‘certain area of the galaxy’ that Neil DeGrasse Tyson has mentioned in the past, but I can’t be sure).
On the other hand, exactly none of the thousand or so planets discovered so far resemble Earth very closely; as far as I can tell humans could not live on a single one of them. So if there is intelligent life on any of those planets it probably won’t resemble humans.
