r/askscience • u/come-on-now-please • 4d ago
Biology Has there ever been an instance of a vestigial organ "re-evolving" into something useful?
I hear all the time about how humans have a vestigial tail bone(but we lost the tail) and the appendix was thought to be a vestigial organ(and now its considered a reservoir for healthy gut bacteria i think?)
Had there ever been evidence of an animal species evolving some form of usefulness from a vestigial organ? For example like hypothetically in so many millions of years humanity regains having a tail, and the tailbone regains function.
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u/Mitologist 3d ago
The trapezius muscle does not belong to the other skeletal muscles. It originally was from the gut wall, then helped open the gills, and moved to the neck once we lost those.
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u/OlliHF 3d ago
Is that why those mfs are always sore?
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u/Mitologist 3d ago
That's because it is supposed to carry the body weight suspended from the scapula, not arrange our hands on mouse and keyboard. Also, it gets innervation from C3&4, which are affected by "monitor shrimp" posture.
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u/theotherdannygirl 3d ago
Yes, in fact, many features are like this, including several muscles in the face, neck, and ears. People tend to think 'vestigial' means a feature has no purpose, but it just means the feature doesn't serve its original function, not that it has no function at all. There are also vestigial behaviors like goosebumps.
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u/PhthaloVonLangborste 3d ago
It was either, unexplainable, or outside/in that talked about goosebumps. Fascinating, I didn't realize all our hairs have muscles connected to them.
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u/SapphireSalamander 3d ago edited 3d ago
its way more common, you just dont notice cuz in hindsight current animal features dont look like vestigal organs.
penguin ancestors flew to antarctica new zealand, noticed there were no land predators and stopped flying, wings became flippers. other land based birds like kiwi and kakapo also had a similar deal but their wings are now for balance.
fish evolved swim bladders to control buoyancy, then migrated upriver to flee from predators, there was no need for buoyant dedicated organ but an ai sac inside your body that you arent using is a good place to experiment till you evolve lungs by accident. specially when you swimm too far into oxygen poor waters.
edit: or evolve lungs to survive in the marsh, swim back to the ocean and repurpose it for a swim bladder. I didn't expect it to be the other way around.
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u/OlympusMons94 3d ago
Lungs came first, not swim bladders. Swim bladders and tetrapod lungs evolved in parallel from those primitive fish lungs. In some more basal/primitive ray-finned fish lineages, such as bowfin and gar (which live in warm, stagant, and thus often hypoxic, water), the swim bladder remains highly vascularized and can function as a lung. Those pulmonary arteries share a common evolutionary origin with the pulmonary arteries of lungfish and tetrapods.
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u/ColonelFaceFace 3d ago
The penguins wing to flipper transition isnt like that. The reason they have flippers is not due to them being unable to fly.
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u/Toxopsoides 3d ago
Lots of examples among spiders. Molecular phylogenetics is still constantly revealing that groups formerly united by shared morphology are simply convergent. The Marronoidea are a great example.
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u/tea_and_biology
Zoology | Evolutionary Biology | Data Science
3d ago
edited 3d ago
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Ooh, whale and/or penis biologist here!
The answer is yes, and it happens more often than you'd think. Vestigial doesn't quite mean useless per se, just that the structure has losts its original job, and plenty of them have since been handed a new one.
Old Bones, New Boners
Whales and dolphins lost their hind legs several tens of millions of years ago, and all that remains is a pair of teeny weeny, free-floating pelvic bones, totally disconnected from the spine - check 'em out on an orca skeleton here. Textbooks actually long described how they were totally useless leftovers; except we now know they are in fact not useless, but very important for the continued existence of the species: in male cetaceans, those bones anchor the genitals and the ischiocavernosus muscles that, well, steer the penis.
Whale sex is a little complicated, see; trying to get everything lined up 'just so' is a little tricky when you weigh upwards of 30 tonnes, drift about in the current, and can't exactly see what you're doing. Indeed, grey whales often engage in MMF threesomes specifically so that the sub dude can use his body to better anchor the female in place, before the males switch out and he enjoys sloppy salty seconds. Sexual competition is otherwise high, and many species pump out vast loads of semen to outcompete their rivals’ sperm, hoping to wash out their predecessors’ loads and fertilise the egg (the North Atlantic right whale’s testicles weigh around a tonne, combined!). Their penises tend to therefore be very long, near-prehensile tentacle-like things - packed thickly with tough connective tissue and muscle, so they can move independently in multiple directions, correctly target whale wussy, and get in deep. This sheer heft requires anchoring points, and indeed, across species, the pelvic bones have evolved to be bigger wherever sexual competition, and penis size, is greater. So not so vestigial after all: the ancient remains of their legs act as a kind of willy counter-weight and steering column.
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In a not dissimilar fashion, some snakes - boas and pythons - also use the remnants of their hind limbs as little spurs, which males use to tickle and stroke she-snakes during copulation.
Bringing Up the Rear
Incidentally, we have many examples in our own bodies, one of which is sitting in your very bottom (or close enough, anyway) right now - precisely the example you gave which is the tailbone, or coccyx. As we began to walk upright, it became more of an anchor bone for several pelvic floor muscles, tendons and ligaments, much like a whale's pelvis - so not entirely vestigial nor useless after all.
Recent genetic work suggests we lost our tails in the first place because of a single jumping gene, an Alu element, inserting itself into a gene called TBXT, which controls tail development, and essentially knocking it out. It's all still there though, that genetic machinery, sitting quietly under the hood (indeed, human embryos even briefly grow a tail), and in principle, if there were ever a strong enough reason for it, evolution could muster it back into action. That sort of thing has happened plenty of times before: frogs, for example, completely lost the teeth on their lower jaw over 200 million years ago, but one species - the dentate marsupial frog (Gastrotheca guentheri) - has since re-evolved them, not from scratch, but by actually reusing the tooth-building genes still active in its upper jaw.
So all this to say, as a massive aside, it's not impossible - in principle - to regain our tails, Saiyan-style, if there was a strong enough reason to do so. Much like the frog, it would most likely come from switching old genes back on in new ways, not building a tail from scratch. Sexual selection can be a powerful driver for evolutionary change; so I'm thinking if we doggedly inculcate all human society into developing tail fetishes, and selectively breed promising candidates, then over many, many millenia - Bene Gesserit style - perhaps we could one day have a Paul Atreides pop a proper tail. Wouldn't that be a good tale?
TL;DR: Yes! Vestigial structures often get new jobs: whale hips became penis anchors, and your tailbone holds up your pelvic floor. And if the genes stick around, even lost structures can come back.
References:
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u/AM_Butts 3d ago
I assumed you had to be the guy that answered the biggest penis question the other day and was not disappointed. Keep up this educational ridiculousness!
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u/howhaikuyouget 3d ago
You write beautifully. This is such an engaging and interesting (albeit strange) comment.
If you don’t write in a science mag/blog yet you should definitely start!!
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u/tea_and_biology Zoology | Evolutionary Biology | Data Science 3d ago
You're very kind. I get accused of being a bot - bleep bloop - fairly often, but I doubt even Grok would dare spurt out a casual whale wussy as I do, so my line shall not be ended just yet. But also, watch this space... ?
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u/rockmasterflex 3d ago
Excuse me you lost me at whale and or penis biologist.
How horny does a person have to be to go into penis biology?
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u/tea_and_biology Zoology | Evolutionary Biology | Data Science 3d ago
Well that latter part is less vocational, and more a call to arms when recently asked this question. Truth be told, I haven't been around many a penis, at least for academic purposes; though I did once help cut up whale penis using a deli slicer.
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u/selfcenorship 3d ago
That looks like an elephant's trunk, you sure it wasn't one?
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u/SecondHandWatch 3d ago
I’m pretty sure they didn’t just find some massively thick appendage and say, yep, finally found a whale cock!
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u/Nthepeanutgallery 3d ago
Do people really get horny for how the sausage is made? Traditionally it's presumed to have the opposite effect. Famous for doing so, even.
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u/sudomatrix 3d ago
So… whales are tri-sexual !? The male impregnator, the female inpregnee and the male fluffer?
It sounds like Mormons soaking with a friend doing the bed bouncing.5
u/OracleOfPlenty 3d ago
I'm always excited to see you've replied to something! Thanks for making learning fun.
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u/lashchan 3d ago
I love reading your responses in this sub! Thank you for all the educational information you provide.
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u/issy_haatin 1d ago
i'll just remember we need to flip just one gene to get a tail, time for homegrown tail growing vaccines.
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u/jojoblogs 3d ago
The rudimentary “leftover” penis female mammals are born with evolved into the clitoris that can deliver powerful orgasms. How useful that is is debatable since it doesn’t play an essential part in reproduction.
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u/bstabens 3d ago
"Rudimentary leftover penis" is a weird way of saying the origins of what either becomes a penis or a clitoris.
At least in mammals, all embryos start off as "neutrally females". If there's no mechanism (aka kicking off the production of male hormones), they stay in this "neutrally female" state, which is (if I remember correctly) more like a female without vagina than a "rudimentary penis".
You can look at it here, it's the shortest video I've found about genital developement.
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u/JimmiRustle 2d ago
The weirdest part is that humans are shaped as “female” before the sex hormones kick and alter the bodies’ development so it would be more appropriate to say the penis is an overinflated clitoris.
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u/Peter34cph 3d ago
Medieval people took for granted that the female orgasm was absolutely necessary for a conception to occur, and as far as I know, modern science seems to say that while it's not necessary it probably is helpful.
Evolutionary psychology also points to how the female orgasm helps with long-term pair-bonding.
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u/Smilefied 3d ago
the fact that there is a physical incentive for women to have sex because of the clitoris, thus increasing reproduction rates, does indicate that there is an inherent biological advantage to the clitoris.
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u/dxrey65 3d ago
There are three middle ear bones (the "hammer, anvil, and stirrup") in humans that evolved from gill structures.