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| Plausibly Alien Biophysics/Physiologies; The confusing depths of exobiology | |
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| Topic Started: Jan 8 2017, 02:04 AM (886 Views) | |
| Sphenodon | Jan 8 2017, 02:04 AM Post #1 |
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Calcareous
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The thing that has always struck me about exobiology is the inherent difficulty in properly representing the utter difference of alien life from that of Earth's in a realistic manner. Namely, the difficulty in making life that is feasible (e.g. not a moving crystal or energy-based entity), yet not sharing too much of a basis in Earthly life (e.g. about everything in Mass Effect). There's a fine line to tread between designing something that can biologically work, can be comprehended by the human mind in a reasonable timeframe (as in, learning the basics of biochemistry shouldn't take reading two to three hours' worth of exposition and explanation), and most importantly, not too convergent with Earth's life. The latter point - coupled with the first two, to some degree - is the purpose of this thread. For starters, one wonders what scale of convergence can generally be believed to occur from the standpoint of two biosystems that have developed completely independently, and to two wholly different planetary environments. A few things, as it stands at this point, seem to be near-universal constants - carbon-based life is the most likely to develop, some form of symmetry is generally more effective in a mobile animal than asymmetry (with bilateral symmetry in particular seeming to reign supreme), etc. But what level of convergence can generally be expected to develop between large Earthly and large alien lifeforms, and what traits/biosystems qualify as convergent as opposed to biomechanically expected? This goes on as many levels as exist in Earth's biology - while primarily four-limbed life is likely to be an act of convergence, what of the mere presence of limbs at all? Perhaps having two distinct reproductive groups of individuals is convergent, but what of the intrinsic physics behind sexual reproduction? Is the very concept of organelle-based, compartmentalized cells one that's likely to be repeated throughout biosystems? What of neural systems and thoughts/emotions in a vaguely Earth-ish sense? Organs? Eating, or other parts of the trophic pyramid? The list goes on. Then, there's the all-but-necessary second half: coming up for logical, novel alternatives for systems for which convergence seems unlikely on such a scale (and for some in which it might be - it never hurts to have alternatives to work with). For instance: regarding the system of a population of organisms tweaking its average physical structure in response to their conditions over time, what if instead of a random system of genetic recombination to cause changes, successive generations of organisms developed slightly differently than their forebears in direct response to their conditions, spreading their changes on to their offspring (which would themselves change slightly to better fit their environment, and so forth ad infinitum) in a vaguely Lamarckian system? Perhaps I'm overthinking this; whatever the case, this might spark some productive (or at least insightful) discussion and/or speculation as for ways to make aliens truly alien, yet still feasible. What do you think? Edited by Sphenodon, Jan 8 2017, 02:08 AM.
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We have a Discord server! If you would like to join, simply message myself, Flisch, or Icthyander. Some of my ideas (nothing real yet, but soon): Refugium: A last chance for collapsing ecosystems and their inhabitants. Pansauria: A terraforming project featuring the evolution of exactly one animal - the marine iguana. Mars Renewed: An insight into the life of Mars thirty million years after its terraforming by humankind. Microcosm: An exceedingly small environment. Alcyon: A planet colonized by species remodeled into new niches by genetic engineering. Oddballs: Aberrant representatives of various biological groups compete and coexist. ..and probably some other stuff at some point (perhaps a no K-T project). Stay tuned! | |
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| Flisch | Jan 8 2017, 02:20 PM Post #2 |
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Superhuman
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These are basically the questions I've tangled with, like, forever. A lot of people say "Everything is possible in Xenobiology, because we have no reference point". This is wrong. We have not only one reference point, but multiple (to varying degrees). We have at the very least three groups of complex multicellular animals on earth. All of them split relatively early. Deuterostomata most likely split from Protostomata before either group evolved segmentation and Mollusca split from Ecdysozoa before any of them could evolve their trademark features, possibly even before any of them evolved advanced organs and blood circulation. These three groups (Though we could also throw in Cnidaria and possibly even Echinodermata into the mix) are as little related to one another as could possibly be for life that has the same origin. While they are not as alien to one another as actual aliens would be from us, they can still serve as a great example of just how different life would evolve on other planets, by looking at their similarities and, most importantly, at their differences. Let's go through both: The similarities: There are some things that are shared among vertebrates, molluscs and arthropods. The most obvious features are cephalization and eyes. Alien life (at least filling similar niches as our "complex three", or X3) would very likely develop a head to serve as the 'sensory scout' for the body and to centralize the thinking processes close together. Additionally, alien life will most likely have eyes (unless they evolve in subsurface oceans like Europa, though it's doubtful life more complex than bacteria will evolve in such an environment), though the actual anatomy of the eyes will be vastly different. Among our X3 we have lens eyes, compound eyes, those weird open eyes of cephalopods, and even the ocelli eyes of arachnids. Eyes, while likely universal, will come in many different forms and it's likely that alien eyes might be even stranger, though still recognizable as such. What else will alien life have? Apart from limbs, the only similarities continue internally. Organs may largely form to fill familiar functions. There will be a digestive system, likely divided into a crop/stomach section to prepare the food intake for digestion and a long bowel section to extract the nutrients. There will be a heart pumping a blood analogue through the body and a lung/gill equivalent, at least in the bigger species. (Arthropods don't have "lungs" due to their size, but it's likely that they could develop them if needed. It really only takes some muscles that contract and expand the gas exchange cavities.) Then there are things that are likely to come up, even if not universally. Hair, for instance, comes to mind. Although fur is mostly associated with mammals, many species of spiders and insects also develop hairy bodies. There is even a species of frog with fur. Some of the feathers and protofeathers of birds and their ancestors also bear close resemblance to fur. Then there are pterosaurs. As such I expect fur-like body coverings to reappear frequently among terrestrial animals on alien planets. You touched reproduction and sex. This is a difficult topic, because I am not 100% sure when sexual reproduction evolved. If we want to get technical, even asexually reproducing bacteria engage in gene transfers, which is not all too different from sexual reproduction, though they lack genders. However, there are multiple groups of animals (and apparently now even a species of bird!) that have more than one gender, or are hermaphrodites altogether. As such, even if binary sexuality is the ancestral state for terrestrial life, it seems as if, despite deviant methods evolving multiple times, binary reproduction has prevailed and stayed dominant, at least among animals. Either way, whether binary sexuality is the original method of reproduction and has stayed dominant, or if it has evolved out of hermaphroditic systems independently multiple times and became dominant, it has proven to be the most efficient method, being favoured by animals of higher complexity. Still, I know too little about this to make final judgement, but it is likely that "X3-level complex life" will also exhibit binary sexuality. The differences: Now that we have covered the similarities, we can look at the differences to see what things are infact NOT universal and possibly even rare among life in the universe. If something has evolved only once on earth, it's likely that that thing is unique to terran life, or at least unlikely to show up in alien organisms. Here's an assorted list of the things off the top of my head: Endoskeleton Out of all groups on earth, a true endoskeleton, as in a supporting structure, has evolved only once, in vertebrates. This may look as if endoskeletons are rare, but in reality, there is at least one other group with an endoskeleton (two, if echinoderms turn out to have evolved their internal sclerites after splitting from vertebrates): Sponges. Although the spicula of a sponge are a far cry from a real endoskeleton, it's not farfetched to think that such structures could quickly reform into a supporting frame by merging together. Additionally, the sclerites of echinoderms are different from the skeleton from vertebrates. The bones of vertebrates (which really started out as fishbones) were an attachment for muscles and to stabilize the gill arches. They existed to support the body. In echinoderms they seem to mostly protect the body, with some additional functions like forming teeth. This difference in applications lead me to believe that both instances evolved independently. Their shared ancestor likely had the metabolic potential to develop such structures, but only after they split had both groups evolved true internal hard parts. If this is true, then endoskeletons, or at least the base for which such structures could evolve, appeared at least three times, independently. This would make it possible for endoskeletons to arise on other planets, but even then their exact makeup will be largely different. An endoskeletal structure evolving from sponge spicula or echinoderm sclerites would be vastly different from one that evolved on the base of a backbone, like ours. Even then, the evolution of an endoskeleton is far from a given, out of our X3, only one group evolved an endoskeleton and the other two are doing just fine. It's perfectly believable that the life on many alien planets will never evolve actual endoskeletons. Exoskeleton If endoskeletons are uncommon-to-rare, exoskeletons are probably even rarer. Actual endoskeletons, with joints and everything, evolved exactly once, and there are no groups outside the ecdysozoa that seem to have the necessary preadaptions for evolving an exoskeleton. Echinoderms are close, but since they have a thick layer of skin covering their endoskeleton, it's unlikely they will evolve a true exoskeleton, maybe some sort of hybrid betwen endo and exoskeleton. If we go by the pedant definition of an exoskeleton, some might argue that bivalves and brachiopods also possess an exoskeleton, but those are very far removed from a jointed exoskeleton and unlikely to give rise to one. As such, exoskeletons seem to be rarer than endoskeletons among life in the universe. I wouldn't say it's impossible to find alien life with an exoskeleton, but they'll likely be rarer than life with endoskeletons. Number of limbs Tetrapods have 4, insects have 6. Arachnids have 8 and myriapods a couple dozen. Crustaceans 10 and molluscs none. It seems as if life can't agree on anything here. Many say that 4 is probably the ideal amount, but I believe that that's a bias. We see that tetrapods get along fine with only four legs and consider that to be the ideal or "default", but tetrapods didn't become the dominant megafauna on earth because of their number of limbs, but because of their endoskeleton. If they had six limbs, things would've turned out similarly. Infact, one might argue, that more numbers of limbs means more potential for specialization. Many of the appendages of arthropods are actually derived limbs, such as the mouthparts, feelers and even gills. Also the tail flukes of lobsters. It's possible that the amount of "redundant" limbs allowed arthropods to evolve into so many different niches in the first place. Similarly, a "vertebrate" group with eight limbs might be able to evolve into more niches more efficiently and quickly than one with only four limbs. Of course, other anatomical features might still play a large role too. Nevertheless, I'm convinced that the amount of limbs is nothing but an evolutionary roll of dice. I expect to see a more or less even distribution of numbers on other planets. One thing I'm on the fence about is an odd number of limbs. I know that many have tried (I did, too), but I have yet to see a satisfactory solution to the "tripedal" problem. Then again, life on earth also evolved odd numbers of eyes, which also seems slightly counterproductive. Feathers This is a super-specific thing, I suppose, but still I've seen it crop up every now and again. Feathers are a complex structure that we still haven't 100% figured out how it evolved. Additionally, feathers have evolved only once in the entire history of terran life. Nothing else even came close. Additionally, the biggest contribution (and really the only form that survived) is a specific form of feathers that coevolved with flight. I wonder what path feathers would have taken, if they would not have given rise to a flying group of animals. They might have stayed bristle-like or even simple enough to be mistaken as fur. If so, we might find proto-feather-like structures in alien life, but might not identify them as true feathers, because they never evolved the forms necessary for flight. Even then, I consider feathers to be a rarity, and flight feathers quite possibly unique to terran life. Viviparity This is something that's been nagging at me for a while. Advanced viviparity (with a gestation period and everything) has evolved multiple times, such as in snakes and some sharks, but only in mammals did it really become a big thing. It is often assumed (possibly by correlation) that viviparity leads to higher intelligence, however it should be noted that some birds, notably raven and parrots are also very intelligent and they lay eggs. All things considered, out of the two "major" groups of tetrapods, viviparity vs oviparity seems to be evenly distributed with only a slight advantage in terms of intelligence for mammals. I'd say it's a draw. Alien sophonts may go either way. Infact, if it werent for mammals, viviparity is actually more of an oddity rather than a common occurence. Conclusion: Alien life will be weird. Vertebrates are closer related to squid than they are to alien life. If octopodes already look freakish weird to us, alien life will simply boggle our mind. Many say that alien life will still have "earth analogues", like things vaguely resembling fish or birds. That may be true in an ecological sense, but their fish will be as anatomically distinct from actual fish as squids are, infact even more so. Fish look like fish, because they use their backbone to propel themselves forward. Krill and squid, which largely fill into the same lifestyle (free-swimming ocean dwelling animals) look so different from fish, that you would never mistake them as fish, not even on the first glance. Same with birds. Yes, we have "bird analogues" on earth as well, in pterosaurs and bats, but those groups all evolved from the same stock, tetrapods. A proper "analogue" would be insects. I doubt that anyone seeing a dragonfly would say that it's a "bird analogue". There's another phenomenon that permates science fiction. On the one hand, they want to make things accessible for the people, but on the other hand they want to make things look alien. This leads to ironically backwards designs. They take things that are universal for life on earth, such as eyes, and take them away or change them drastically. This is done to make things look alien. After all, what is more alien than something that shares nothing with earth life. Unfortunately they cannot think outside the box and give those aliens features that are very terran, such as endoskeletons or exoskeletons. Essentially they deviate from something that is likely going to be universal, but on the other hand stick to something that evolved only once on earth, due to their inability to think up something new. A good example is the animal life on Darwin 4. They all lack eyes for no reason, but yet they all have an internal skeleton. It's basically the wrong way around to tackle the problem. Then again, it's hard. It's really hard to come up with something plausible that did infact not evolve on earth. If arthropods would have never evolved, who would think up such a thing as an exoskeleton? If vertebrates never had, who would get the idea for a backbone? This isn't even thinking about all possibilities anymore. It's about coming up with things we don't even know are possible. (Originally I prefaced the post saying "I won't go into too much detail." That was three hours ago...) |
| We have a discord. If you want to join, simply message me, Icthyander or Sphenodon. | |
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| Arawak | Mar 26 2017, 11:45 AM Post #3 |
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Newborn
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The problem with speculating on alien life simply is that there isn't even even knowledge of the range of worlds where life can occur to begin with. An de seeing all the fucked up shit that appears on earth there's no real reason to believe a world with a strong gravity well and thick atmosphere wouldn't have niches that have simply no earthly equivalent. There'd be some similar stuff as aforementioned posts have pointed out... but the huge gap of unknowns really does no favors for narrowing down what can and can't exist. Oh and don't forget all the phyla that died out that never got a chance to develop further on earth so even extremely earth-like worlds may have things that go down non-convergent pathways. I think that even making vague archetypes for biospheres will take analyzing hundreds of worlds with complex life as the range of things that may exist simply is unknown. It's not even clear what sort of planets can exist in the universe still. Yes rock and gas planets, but the details are what matters and you never know what might exist. For instance would any speculators of alien worlds predict a world like Titan without seeing Titan firsthand? Same with alien life. The range of habitats is unknown, how can you even begin to predict the range of what can and can't exist outside of seeing the current range of possible life earth offers. Sure you can predict vague trends like how gravity and air pressure may affect biospheres, but there's still a lot of X-factors current science can't acutely fill in. That being said I believe that speculations probably do predict actual aliens somewhere in the universe all the time but the context of the biosphere in loved still may be remarkably different. |
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Oh look, links! Please no click the deviant art Please no click the Tumblr, you are just enabling him! | |
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| Sceynyos-yos | Mar 26 2017, 12:08 PM Post #4 |
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dheubewes wedor
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I disagree that skeletons, be they endo- or exo-, would be rare, as they are quite useful. Any tiny bit that goes toward evolving a skeleton would give the clade a competitive edge, allow it to spread and diversify more and increase its chances of evolving the next step. Rinse and repeat and not before long you've got a functional skeleton. I do agree, however, that any alien skeletons will be, well, quite alien. A skeletal system that features endo-, medo- and exo- parts is on the menu, likely many times over. |
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| gestaltist | Jun 22 2017, 01:27 AM Post #5 |
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Adolescent
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Now I want to see a project that really thinks about skeletons. Hell, you just made working on Scosya all that harder for me.
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| Scosya - my project | |
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| trex841 | Jun 22 2017, 07:27 PM Post #6 |
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Entity
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So I asked about this in the Questions Topic, but since this is an actual topic for it I wanted to see if there were any second opinions on the issue. Long story short, I was curious about any possibility for Silicon based life, and Holben believes that the only way it could work would be to make it Carbon. I also asked about other potential elements, but that's when the conversation died. |
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F.I.N.D.R Field Incident Logs A comprehensive list of all organisms, artifacts, and alternative worlds encountered by the foundation team. At the present time, concepts within are inconsistent and ever shifting. (And this is just the spec related stuff) | |
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| opeFool | Jun 22 2017, 07:51 PM Post #7 |
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Adolescent
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Well, there go months of planning out the window... |
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Xipetotec | Mbio Bila Mshindi | Diarios California Quotes
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| LittleLazyLass | Jun 22 2017, 08:58 PM Post #8 |
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Proud quilt in a bag
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Not exactly, or at least not necessarily. Animals like oviraptorosaurs and dromaeosaurs had feathers more or less just like those of modern birds (although lacking a small amount of small features like asymmetry), and although a flying ancestry isn't impossible, it remains a fringe claim. The general design of the modern bird feather didn't evolve for flight, so far as we know. Not really relevant, but thought I'd bring it up. |
totally not British, b-baka! You like me (Unlike)I don't even really like this song that much but the title is pretty relatable sometimes, I guess. Me What, you want me to tell you what these mean? Read First Words Maybe | |
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| Inceptis | Jun 23 2017, 10:42 PM Post #9 |
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In-tro-vertebrate
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Something that is surprisingly common is a hydroskeleton, which is odd, because you never really hear about it. If you've been told something has no skeleton, it has a hydroskeleton. Cephalopods, most cnidarians, and a lot of spiralians all use water pressure and muscles to regulate their shape. While this doesn't seem ideal, as it is hard to maintain in air, look at octopuses. They're the most intelligent invertebrates on the planet, and if vertebrates had been stunted early in their evolution, I daresay they would struggle to compete with cephalopods in general, maybe even pushed to backstage. So, it obviously leaves plenty of room for specialization. |
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This was getting fairly big. Spoiler: click to toggle
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| trex841 | Jun 24 2017, 07:27 AM Post #10 |
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Entity
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https://canopy.uc.edu/bbcswebdav/users/gibsonic/Snaiad/sndanatomy.html Oh wait, duh, that's clearly hydromuscular, I'm an idiot.
Edited by trex841, Jun 24 2017, 09:29 AM.
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F.I.N.D.R Field Incident Logs A comprehensive list of all organisms, artifacts, and alternative worlds encountered by the foundation team. At the present time, concepts within are inconsistent and ever shifting. (And this is just the spec related stuff) | |
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| Inceptis | Jun 24 2017, 05:17 PM Post #11 |
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In-tro-vertebrate
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Another thing that's really common but not at the front of your mind is filter feeding. Though size somewhat blurs the line, nearly every single phylum has at least one filter feeder in it. Clams, barnacles, tunicates, feather stars, pterobranchs, even Symbion: they're everywhere. The only ones I can think of that this doesn't apply to are nematodes, flatworms, and limnognathia. EDIT: So, it's obvious you need to pay attention to plankton. On a biochemistry branch off the topic (which I'm kind of terrible at anyway), pretty much all life on Earth utilizes the proton and the electron for being active, which means they're likely to be used as well in alien biochemical processes. Edited by Inceptis, Jun 25 2017, 07:27 PM.
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This was getting fairly big. Spoiler: click to toggle
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