🧵 Xenobiology
Anonymous at Sun, 28 Jul 2024 18:00:24 UTC No. 16300606
Sci-fi shows, movies, and vidya come up with all sorts of designs for aliens. Some fall back on the tried-and-true strategy of just gluing random bits of latex to peoples' faces, some are ridiculous CGI monsters, and many fall somewhere in-between. But what might other technological, spacefaring species *realistically* look like?
To the various -ologists of /sci/:
1. What are the common physical, mental, and social traits that a technological, spacefaring species will need to have?
2. What are the practical mechanical, biological, and evolutionary limits on what forms could develop?
3. Based on the above - what could members of such species look like (or *not* look like)?
Anonymous at Sun, 28 Jul 2024 18:04:03 UTC No. 16300610
Large brain to body size ratio
Fine control manipulation appendages
The rest is more optional depending on how stuff happened to evolve.
Tetrapod? Octopod? Stands up? Centaur style? Doesn't really matter as long as they have fine motor control and are smart
Anonymous at Sun, 28 Jul 2024 18:05:28 UTC No. 16300616
>>16300606
Centaurs.
Anonymous at Sun, 28 Jul 2024 18:24:05 UTC No. 16300645
>>16300606
Based on available evidence they will likely be just like us, more or less anyways e.g. just us with latex or furry suit on. That's simply due to our features being determined before we were intelligent and being set by laws nature. For instance 4 appendages are the most efficient configuration and so is symmetry, this automatically leads to 2 hands and 2 feet for any intelligent, tool making mobile creature. 2 eyes is the same thing, breathing gas is much better than liquids so it will be a land animal. They will have a head with said eyes and brain because visual processing takes so much energy and because central control will lead to intelligence fastest. They will be an animal (e.g. not a plant or fungus) because of the need to generate energy fast, likely omnivore with a medium sized social group because intelligence helps the most with that kind of lifestyle. etc.
I think a good approach is to just take an earth animal, make it human sized, stand up on 2 legs and if required change the front legs to hands in case of 4 legged animals. That's your base form. Then the variation comes from if you are talking about a lizard man or bird man or cat man etc which will then generate their base behavior and diet but the fundamental layout is going to be largely the same.
Of course we only have 1 data point so far and while it's safe bet to think that our situation is fairly average it's not required to be so, but it's dumb to presume everything other than greys and space furries for now.
Anonymous at Sun, 28 Jul 2024 18:31:41 UTC No. 16300651
Any technological species needs to evolve in an environment that physically permits the development of certain tools and technologies - fire, metalworking, chemistry, electricity, etc. - which necessitates living and working in a mostly-insert, moderately-oxygenated atmosphere.
That kind of rules out scenarios with purely-aquatic species or species evolving on worlds with exotic, corrosive, or highly-reactive atmospheres.
Anonymous at Sun, 28 Jul 2024 19:39:52 UTC No. 16300766
Anonymous at Sun, 28 Jul 2024 20:37:17 UTC No. 16300860
>>16300766
Interested in the scientific discussion, not the creative writing discussion.
Anonymous at Sun, 28 Jul 2024 21:11:23 UTC No. 16300904
>>16300606
Gaseous ants are the norm in our local universe, tho.
Anonymous at Sun, 28 Jul 2024 23:43:32 UTC No. 16301114
>>16300610
>Doesn't really matter as long as they have fine motor control and are smart
In theory, no, but in terms of optimization an excess of limbs for locomotion reduces your brain-to-body size ratio. If you're dedicating a lot of energy moving 4, 6, 100 limbs to move around that's less energy to devote to a large, neuron-dense brain.
Anonymous at Mon, 29 Jul 2024 00:21:45 UTC No. 16301168
>>16301114
No one says evolution is optimal
Anonymous at Mon, 29 Jul 2024 00:29:44 UTC No. 16301177
For your troubles:
>>>/an/4833788
Anonymous at Mon, 29 Jul 2024 01:01:42 UTC No. 16301216
>>16301168
Optimal, no. Optimizing, yes.
At the end of the day if you want conditions that will select for higher intelligence, having a body design which requires devoting most of your resources and energy towards growing, maintaining, and moving extra limbs is likely to hinder such a selection. Locomotion for land-based animals with six or more limbs (be it walking or flying) is significantly less efficient than for tetrapods.
Anonymous at Mon, 29 Jul 2024 01:38:30 UTC No. 16301248
>>16301114
>>16301216
Some points to consider:
- limbs do not have to have a uniform size or complexity
- any number, including zero, limbs may or may not be used for locomotion
- limbs may be autonomous or even entire organisms
More than nature being inefficient, I'd emphasize that nature is *weird*. Every point I make refers to real lifeforms present on Earth. Nature does not care to appear sensible or sane.
Anonymous at Mon, 29 Jul 2024 03:18:08 UTC No. 16301330
>>16301216
>Optimizing
only in regards to directly beneficial or harmful alterations, determined by the LOCAL fitness landscape, and only as long as that landscape remains static relative to the fitness consequences of the change in question. certain dimensions of the landscape are static, but there's basically zero evidence that "4-limb optimality" is one.
>>16301114
tetrapods are genuinely just a consequence of 1. evolving from a fish clade with 4 fin lobes and 2. the extreme difficulty of increasing limb count on land for morphological and developmental reasons (without an explicitly segmented bodyplan).
it's much easier to selectively reduce a pair of limbs in a vertebrate than it is to develop new ones, not because "more than 4 is suboptimal," but because selective limb reduction combines the ease of size change in response to selection pressure with the 'ease' of structure specialization relative to structure formation.
but probably the biggest barrier to evolving extra limbs is the fact that the tetrapod digestive, respiratory, reproductive, circulatory, and skeletal systems are already internally specialized for AT MOST two pairs of DIFFERENTIATED limbs - one anchored at the front of the thorax, and one anchored at the back of the abdomen. this likely arose incidentally in aquatic tetrapods, but became almost unchangeable for those living on land. there just aren't internal structures to anchor any proto-limbs - land necessitates those in a way that water doesn't, further driving internal specialization. the likeliest source of extra limbs anywhere - copying an existing pair - are, given highly specialized internals, nearly certain to disrupt internal structure, harming survival REGARDLESS of the viability of a hexapod, likely outright making the embryo nonviable.
hexapod land vertebrates aren't a suboptimal bodyplan, but rather a nearly impossible evolutionary pathway for the fish clade that happened to monopolize land niches first. that's all.
Anonymous at Mon, 29 Jul 2024 04:20:43 UTC No. 16301391
>>16301330
(cont.)
some examples of my point here: leglessness has evolved multiple times in lizards, a largely 2-limb bodyplan has evolved in dinosaurs at least twice (flightless birds without wings, and the diminutive limbs of certain large theropods), and a completely 2-limbed bodyplan has evolved in cetaceans. note that in all of these examples, despite diverging from the "4 limb optimum", not ONCE have any of them diverged from that "one pelvic anchor, one shoulder anchor" paradigm - when snakes and cetaceans occasionally express the lost limbs (which does happen), they are exactly at those unused anchor points.
it cannot be overstated just how fundamental that pattern is to tetrapods - it appears BEFORE the vertebrate land invasion, deep in early tetrapodomorpha, as it is essentially the same selection pressure that led to the robust skeletons of the amphibious ancestors of tetrapods. tetrapod limbs on land require a bony girdle, and the pressures and preexisting structures on early tetrapods led to the development of (and specialization around) only two: pelvic and shoulder.
other osteichthyes groups don't really have those structures because in water, their limbs can anchor to muscle. with similar fin structures and minimal other requirements, an extra pair of fins isn't itself likely to kill the fish, and is fairly easy to select for or against. a lot of osteichthyes are effectively "pentapods" in regards to their ventral fins (singular anal fin), but it just so happened that the clade with lungfish ALREADY lacked an anal fin, and that clade is where ALL terrestrial vertebrates came from.
if tetrapods could have ever been hexapods, it was likely only from retaining and splitting the anal fin. perfectly possible - but not an option for the clade that ended up dominating land, as they'd lost the anal fin already.
if you were curious, yes - you ARE a fish. specifically a bony fish (osteichthyes), and more specifically, a lobe-finned fish (sarcopterygii).
Anonymous at Mon, 29 Jul 2024 04:38:46 UTC No. 16301402
>>16301391
(cont. again)
it's pretty easy and amusing to imagine a universe where a sapient species with tripod legs that evolved from bony fish that retained the anal fin are arguing that intelligent life could never have 4 limbs - after all, tool use requires spare manipulator limbs, two is necessary for effective tool manufacture, and obviously an animal with only 2 locomotive limbs would be unable to balance itself without spending energy constantly, reducing the calories available to their brains.