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Anyway, I'm playing subnautica and it goes something like this. you're traveling in the aurora an interstellar special ship, but due to some event you become stranded on a planet filled with water and I've been discussing with my friend, could we be able to adapt to the environment and maybe become more mermaid like, we also talked like certain adaptation we might have after a few generation nothing big but a few such as being able to hold our breath longer, etc, but could we adapt to the point where we become a mermaid

Yes there is enough fauna and oxygen in the environment to sustain ourselves.

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    $\begingroup$ Good news and bad news. Good news, there are plenty of questions on this site that answer your questions here. Bad news, your question will probably end up being closed if you don't take that into account and edit accordingly. $\endgroup$
    – Alendyias
    Jun 7 '21 at 19:38
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    $\begingroup$ Technology is your best tool to adapt to environment, it is flexible and fast and the only way in few generation time. Do u understand that evolution means premature deaths of many those who are less adapted, so next 10-20+ million years will be quite harsh for your people. $\endgroup$
    – MolbOrg
    Jun 7 '21 at 20:10
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    $\begingroup$ Also what do u mean more specifically, real mermaids with scales fish tail hands and chest plate, or just better sea adaptation, and appearance does not matter. First case answer is no, second answer is yes, based on examples of such cases, and some tribes. $\endgroup$
    – MolbOrg
    Jun 7 '21 at 20:24
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    $\begingroup$ Easier than you think! :) $\endgroup$ Jun 7 '21 at 22:25
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    $\begingroup$ Dolphin, Whale and Manatee says yes. The fact that they took 50 million years to do so, says.... no, you are almost certainly not patient enough. $\endgroup$
    – PcMan
    Jun 8 '21 at 20:40
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I remember reading somewhere that some scientists think that homo, at a certain point of its evolution, went through a semi-aquatic type of life. If I remember correctly this is thought to explain some features of our body, like the immersion reflex or the disposition of our body hair.

No matter if that theory is correct or not, we have examples of mammals who have adapted to become fully aquatic (dolphins and whales among others) or partially aquatic (seals and walruses, for example). So it's not totally peregrine the idea that, with the right pressure, our evolution can continue in that direction.

However that won't happen over few generations. It will take several generations to have a noticeable change. For a reference, despite about 10 thousands years of evolution, we are practically still the same species who invented agriculture.

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    $\begingroup$ This is the aquatic ape hypothesis: en.wikipedia.org/wiki/Aquatic_ape_hypothesis If you dig it, read more in Scars of Evolution by Elaine Morgan. I found it convincing. $\endgroup$
    – Willk
    Jun 7 '21 at 21:52
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    $\begingroup$ First time I've noticed "peregrine" being used in a sentence other than referring to the falcon, I needed to look up the meaning! And yes, it takes a minimum of thousands of years after a human population migrates to more/less sunny areas to evolve a perceptible difference in skin pigmentation, much, much, much longer to get functional changes like increased lung capacity or webbing between digits. $\endgroup$ Jun 7 '21 at 23:51
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    $\begingroup$ “For a reference, despite about 10 thousands years of evolution, we are practically still the same species who invented agriculture.” However, there was not significant evolutionary pressure to change. If people who can’t hold their breath for more than two minutes die at a very high rate you’d probably see an improvement pretty quickly. $\endgroup$
    – Michael
    Jun 8 '21 at 5:46
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    $\begingroup$ @Michael it’s more likely that just everyone dies in that case. It needs a very large population for such an adaption under high pressure, not just the crew of a stranded spaceship. $\endgroup$
    – Holger
    Jun 8 '21 at 13:52
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    $\begingroup$ @Holger there are entire tribes (polynesian?) that can hold their breath for several minutes (because they have a larger spleen). $\endgroup$
    – Mixxiphoid
    Jun 8 '21 at 13:57
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Well, relatives of cows and pigs did, in the space of around 50 million years. So in general yes; but humans have a particularly shallow gene pool so we, in particular, could not. You'd have to introduce a way around that to accelerate viable mutations.

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    $\begingroup$ Real problem, more so for stranded spaceship. U probably can extend your answer by example of plants selection process and sucesses prior dna and gmo $\endgroup$
    – MolbOrg
    Jun 7 '21 at 22:08
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Probably not.

The issue is primarily that humans lack a functional tail, having only a coccyx fused to our sacrum that does very little other than anchor some of the pelvic floor muscles. There's nothing for evolution to act upon because there is no variation within the population to select upon. Vestigial atavistic "tails" have been documented in humans, but most of them aren't actually tails but form from a pathological malformation of the spinal column (and aren't even inheritable). Even when "true tails" do reappear, they lack any sort of bony structure necessary for swimming.

I've heard it said by other people that a fully aquatic posthuman would end up looking more like a frog, grebe, or a sea lion/walrus. All of these animals have very short tails, but became marine by way of developing large flippers on their fore and hind-limbs. Humans, when they do swim, tend to be most efficient at a frog-like breaststroke anyway. Seals also have short tails and do have mermaid-like bodies, with the feet turned into a functional equivalent of the tail fluke, but they do this by having their pelvises located way at the back of their skeleton. Humans have very large and bulky pelvises due to our large-brained infants (and assuming your mermaids appear somewhat humanoid on their upper half the mermaids might as well). This would create a large bulge at the terminal end of the body and disrupt a fusiform (torpedo-shaped) body outline, which would increase drag while swimming.

You could honestly achieve a true mermaid a lot faster by genetic engineering. Have the ship get stranded on some area where most of the useable resources are underwater, and the travellers end up genetically engineering their offspring to be able to thrive in this environment. This would be very easy as human embryos have a very large tail (like all vertebrate embryos) that later gets resorbed into the body. You wouldn't even have to edit that many genes, just reactivate and repair the old fish genes that have degenerated since humans left the water.

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  • $\begingroup$ Whales and friends lack a functional tail as well. $\endgroup$
    – fraxinus
    Jun 8 '21 at 7:42
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    $\begingroup$ "human embryos have a very large tail" sorry, no they don't; they have a spine that hasn't yet grown legs. That particular bit of BS has been debunked for a long time but still gets repeated with alarming frequency. $\endgroup$
    – Matthew
    Jun 8 '21 at 12:49
  • $\begingroup$ Matthew comment makes a lot of sense actually, I was suprised by that part as well, but Matthew's comment perfectly explains Sirenomelia, which was linked in comment to the q by Mike Serfas, so I even do not need to click the link to see the point is a correct one. Your part in that regard is not entirely wrong, but it can benefit from more correct wording/view on it $\endgroup$
    – MolbOrg
    Jun 8 '21 at 13:23
  • $\begingroup$ @fraxinus Incorrect. They have a huge tail that takes up more than half of their body. Their tail fluke is...well, a tail fluke. What whales lack are functional hind limbs (the pelvis does little except anchor some urogenital muscles). $\endgroup$ Jun 8 '21 at 16:18
  • $\begingroup$ @Matthew They have a postanal tail. Check out the answers and posted pictures in regards to this question. I looked up what you mentioned and the only people who seemed to be saying it was not a tail were creationists. Just because Haeckel was wrong in the broad scope of his recapitulation hypothesis doesn't mean he wasn't right in some of his observations. $\endgroup$ Jun 8 '21 at 16:36
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The basic answer is No. ... But

There was a series of short stories written some time ago about this scenario (cant remember the name of either the book or the author). The stories were set in the far future where humanity has mastered interstellar travel but Earth like garden' worlds perfectly adapted to supporting human life are very very rare.

There are lots of marginal worlds i.e. to hot or cold, to high a gravity toxic gasses etc where humans could only survive with the aid of technology (domes and breathing devices etc). Alternately they have incompatible bio-chemistries i.e. they have complex ecosystems like Earth but with different/incompatible metabolisms. So Earth's plants and animals can't compete/survive easily and the local stuff is inedible.

Anyway, instead of trying to adapt the planet to human life i.e. Terraforming the answer is adapt humanity to the planet. (Terraforming is still done BTW in some rare cases where the changes required are relatively easy. In general however its considered to be too hard or too long term a process to be worth the effort.)

So they gene engineer embryos (both human and other Terran animals and plants deemed essential for survival) to be capable of surviving on the surface of a selected planet. The result is a galaxy filled with races who look nothing like human beings but who are the descendants of the original colonists or explorers.

One story even tells the tale of a ship that crash lands on a water planet. The crew know they are doomed but while they still have time they modify embryos to produce merpeople and then seed the ocean with them - leaving only records behind to explain how they got where they are and why they are so different to all the other lifeforms on the ocean world.

You could certainly go for a line of hippo or seal like lifeforms.

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Wasn't willing to write an answer to the q, as OP clearly has no idea for how much blood and suffering he subscribes to those guys for a period from 100'000 years to 10-20 million years.

So as the approach basically condemned by almost everybody unconditionally, and what should take place is worse than it by an order of magnitude. For that reason, I won't dive into gruesome details.

The reason I decided to write an answer because current answers and comments are soo close to naming it, but they didn't. Another reason is its good example of how pointless it is with genetic modifications(which more humane way) or without it, in a hard way as OP wants, I guess, as OP didn't clarify and probably long forgotten he asked it on WB.

End of intro, real deal now.

Eugenics

Basically, it is the same selection breeding process we use for dogs, cats, domestic animals, but for humans, with or without some belief system attached to it.

  • and it requires it as they need to eliminate(kill) people who do not fit, 10x This is Spaaartaaaaa way, be like Aztec's guys who did human sacrifices out of the belief that if they do not it then a sky will fall. It could have some sense for their way of life and situation, as population regulatory mechanism, so it, not total nonsense, words are wrong but. But with eugenics on our planet is a road to nowhere, but on an OP's planet/idea it is the way to keep going.

First success stories dogs, cats, especially dogs as it is easier to crossbreed them there are many different kinds of dogs, few thousands to be more specific, and they have different builds and exteriors, from tiny tiny things to quite big ones.

Sure we breed them to be dogs, so they still dogs, after 10000 years. But if one has quite a pool of genes and incentives to do so it possible to shape them quite fast, through selective breeding to a variety of dogs. And if you look at well-known breeds of dogs, how did they look a hundred or two hundred years ago you can see the differences easily, they can be quite full of changes - no wings obiviously, but it just 100 years.

So a thing everyone forgot about humans, in their answers or comments, me included - is The Brains

We aren't animals, who need to evolve mindlessly, they do not have enough brains to judge things, but humans do.

The bad news however, potential speed of changes in dogs is about 60 times faster than for humans - 1.5 years dogs can be considered mature, and it brings 4-6 pups each year. Humans 15 years, once 2 years, 1 kid typically, soo even cows are 10 times faster(3y maturity, 1 calf, each year)

Some problems

JDługosz in his answer correctly mentions that diversity of genes will be a problem, indeed, but he decided to be short and didn't explain, so I will do it.

Before humans knew what DNA is before we knew how to make GMO - the plant selection process was quite long inaction, and actually was or is modeling process of inheriting properties and indirectly pointing on existence of genes for guys back in the days who tried to work out the logic behind the process.

Due to different mutations over millions of years, plants do(or did in some cases) have enough of gene diversity, and some combinations of those collected together do create breeds of apples we know today, avocados, bananas, that thing full of seeds we make breed from, etc.

Significant improvements were achieved by the selection process, randomly(not exactly) taking some combinations out of many many possible ones for that gene pool and working on improving or dismissing results.

Avocado is quite a prominent example. Random, meaning typical avocado guy/tree tastes like trash, out of the whole population of avocados trees only some taste good, meaning there is a big enough pool of genes, but only specific combination tastes good enough to be sold. And what is sold are products of clones of a specific member of that avocado population, and if you breed one in a natural way(seed) from those there is a very slim slim chance(0) to get good tasting one.

  • meaning - if avocado trees would be humans, and we would be vampires, then nice tasting ones would be, maybe, red hairs with a good smell in their armpits.

Stranded spaceship indeed may have no diversity of genes, and they will become even poorer in that aspect each next generation, well-known problem for generation ships, discussed here multiple times, and it is a bridge to cross and not to do die out, but Australian tribes do show it possible.

But if they get their numbers up, then they do not have to rely on mother nature to enrich them with mutations, drink more C2H5OH and it increases the probability of mistakes in chromosome divisions and mutations. So the rate of mutations can be increased by behavior, so as finding more potent sources and ways, meaning it does not necessarily has to be radiation, mundane chemicals can do that as well.

Big problems

The most gruesome part of all that will be the selection process, it far beyond the typical imagination of a human ... what? What did u say? Ahh - nazi, cannibals, pirates, mengele, italian mafia, narco cartels - no no no, those are innocent kids.

I do believe op just innocently didn't think about those things through, and was captivated by Disney, but the truth behind that is ...

But things are worse than, how can it be - do you ask, well suffering for meaningful cause can be justified, but this one, ...

We really have to be grateful to our ancestors, they did have a hard life, by those ancestors I mean even those well in the past, maybe even not homo erectus.

The human species got two things right - brains and tools and through their efforts and ingenuity and hardships and application of those two things - we are where we are today. Yes, there is a long road ahead as well, but because of applying brains to the usage of tools and ideas I can type my answer in the comfort of my home for you to read, instead of being in a cave or on a tree thinking which predator will try to eat me today.

Thank you to all our ancestors! Hallelujah! Your collective work made today possible! Hallelujah!

Special thanks, from me personally to you, NoName guy, who made stone knife and equipped humanity with Claw's, and to you who made Atlatl - you guys are great, you did the life of humans easier and survivial possible. It not necessarily was a big step for you guys, but it was a jump into the sky for humanity.

OP what do you think your stranded descendants will tell about you?

Use technology, few thousand years and you will make a pancake out of that planet if it will be what's your desire.

P.S. People feel themselves quite well on the water this is one of the examples https://en.wikipedia.org/wiki/Sama-Bajau

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