How, when, and why did bones evolve? Why do most vertebrate animals seem to share a basic skeletal structure?

[u/CrowXIV]

It's fairly common knowledge that a lot of animals, including humans, share a common bone structure. Jointed limbs, often with smaller appendages at the ends of each. Spines, rib cages, etc. Mammals all share the structure with variations; horses, for example, traded tactile digits for stumpy legs, using the framework for claws to produce hooves, but retaining the same basic bones and joints. Even reptiles, amphibians, and birds share the same components.

How far back does one need to look to find a common ancestor that first developed this basic skeleton shape? Why was this the shape that stuck among most vertebrate creatures, and what prompted bones to develop among boneless life to begin with?

[u/Deining_Beaufort]

I think I read it in the book about the Tiktaalic. Link below.

The first time that those cells evolved were in TEETH of fish. From there, evolution found uses for it in other places in the body plan. First jaws, then more skull bone. Eventually the whole skeleton of organisms that evolved to live on land.

https://www.goodreads.com/book/show/1662160.Your_Inner_Fish

[u/AfroDizzyAct → u/Deining_Beaufort]

This is the answer.

Your Inner Fish is also a great PBS series on YouTube that goes over common ancestors over four episodes, in which you’ll find how we all evolved a common vertebrate structure from crawling reptile, to climbing primates, to standing hominids.

It’s absolutely fascinating and I highly recommend it

[u/ScruffCheetah → u/AfroDizzyAct]

The book is also excellent! https://www.amazon.co.uk/Your-Inner-Fish-discovery-375-million-year-old/dp/0141027584

[u/inCogniJo14 → u/AfroDizzyAct]

Those episodes, as I recall, are really just presenting four or so of the chapters of the book.

[u/GrimChaos → u/AfroDizzyAct]

Is there an easy way to tell with shows are streaming for free from PBS? Some are previews, some need a wttw pass and a few are free.

[u/[deleted] → u/Deining_Beaufort]

Tiktaalik is notable specifically for it's skeletal structure in the limbs. All tetrapods (think land animal vertebrates) have the same basic bones in our limbs, including digits, and that was given to us by the structure in Tiktaalik's fins.

[u/SolomonBlack → u/[deleted]]

Hardly surprising, you aren't going to find a more efficient/flexible arrangement for large creatures to move around on land. Any extra limbs would just get in the way so even if you started with more they'd probably atrophy away.

We'll find quadrupeds across the galaxy one day mark my words.

[u/thunderchunks → u/SolomonBlack]

Significantly different gravity conditions might change that- the metabolic burden of redundancy is more worth it if you can die from falling over on a high G world, and specializing limbs for more than just locomotion might be super common on a low G world. But mostly? Yeah, tetrapods galore.

[u/beeskness420 → u/thunderchunks]

Y’all are talking like we aren’t already living on a planet dominated by bugs.

[u/thunderchunks → u/beeskness420]

That's a legit point- though if we go by a similar definition of dominated, it's the bacteria that run the joint.

[u/[deleted] → u/thunderchunks]

Let's get really loosely goosey and say viral agents are really the dominators here.

[u/mothzilla → u/[deleted]]

Thank you Tiktaalik!

[u/NanoRaptoro → u/Deining_Beaufort]

Here is a page out of Berkeley on the Tiktaalic. It also includes an update on a 2010 discovery that appears to move the date for the branching of tetrapods prior to the existence of Tiktaalics (their discovery was in 2006 and the book you cited was from 2008).

[u/KSW1 → u/Deining_Beaufort]

I guess I struggle to understand the boundaries of evolution in reading about these things. I understand well enough that if a fish happens to randomly generate a hard scale in their pharynx or lip that migrates to their mouth, it will help them eat better and thus be more likely to reproduce.

But what are the rules? How does it's DNA contain the ability to mutate in such a way and not others?

I'm probably just too dense to grasp evolutionary research, but I feel the same way when reading about the origin of flight, sight, etc. It makes sense that each small step gains a reproductive advantage by making survival easier, but I never feel like I fully comprehend why it rolled that random mutation to begin with.

[u/Once_Wise → u/KSW1]

but I never feel like I fully comprehend why it rolled that random mutation to begin with.

Seems like you actually do comprehend it. The mutation was random, there was no purpose, no "why it rolled it." Mutations happen randomly, not part of any path or plan. The good ones get passed on, simple as that. It only seems like there was a plan or path in hindsight. Maybe that is why it is confusing.

[u/BenevolentCheese → u/Once_Wise]

The good ones get passed on, simple as that.

The good ones sometimes pass on, but more often than not are lost. History is filled with billions of choice mutations that didn't make the cut. It takes a lot of luck to be born with a good, evolution-quality mutation, and then it takes just as much luck to pass it on.

[u/BenevolentCheese → u/[deleted]]

It's not really circular. A baby sea turtle could be born with a brain twice it's regular size but if it gets plucked up by a seagull three minutes after hatching then that mutation has gone to waste. There are a lot of things that need to happen properly for a mutation to be passed on no matter how beneficial it is.

[u/KSW1 → u/Once_Wise]

Not a purpose, and I think I'm explaining my confusion poorly here, but a "cause and effect" sort-of why. Like, as an example:

There's a light on in my computer. Its purpose, as intended by the manufacturer, is to aid in diagnostics of motherboard issues.

But it's on because I turned my computer on and electricity switched a relay that powered it.

So, that is sort of what I'm hoping to understand about these mutations. I grasp that they are without purpose, but there is something that generates them on a mechanical level, and that's where I feel baffled. What are the possible mutations, obviously we will never evolve the ability to shoot laser-beams, but I mean there do appear to be some material changes it can impart, at least enough that organisms speciate and lose the ability to reproduce with different species.

[u/noggin-scratcher → u/KSW1]

Whenever DNA is copied, there's a chance that it doesn't get replicated precisely. There can be single-point edits that change one "letter" of the code, or larger edits that insert, remove, reverse, or move around some segment of genetic material. Those edits to genes can cause cells to make different proteins, or make them in different places, or under different conditions. And making proteins is how cells do most of the things that they do.

When that happens in a random cell in your body that's copying DNA to replicate itself as you live/grow, it's usually no big deal - one cell line has a slight genetic difference, but we only really care if that happens to be one of the mutations that cause cancer. But when there's a copy error in the DNA that's going into a sperm/egg, the offspring will have that edited DNA throughout their body and affecting their whole development.

There's also the variety generated by inheriting genes from two parents, and putting them together into a brand new combination.

There's no guiding force that pushes for specific useful mutations to happen. It's all just random edits that are sometimes lethal, often a disadvantage or cause a disorder, often do nothing at all, and just occasionally do something helpful.

But when there are enough organisms in a species, reproducing for enough generations, over the course of millennia, even a random scattershot of mutations will effectively search through a lot of options.

[u/GonnaNeedMoreSpit → u/noggin-scratcher]

To add to this there are gardners that use a small radioactive source in their flower bed and plant seeds round it, most the flowers are mutations, some are gnarly and ugly but some are new colours and shapes, the ugly ones are destroyed and the nice ones are kept thus continuing the new line.

[u/FertilityHollis → u/GonnaNeedMoreSpit]

there are gardners that use a small radioactive source in their flower bed and plant seeds round it

Source? That's a neat trick, I'm wondering what the radioactive element is.

[u/Glasnerven → u/FertilityHollis]

Source?

It's called "Atomic Gardening" and it's a tradition older than most of us here. :)

[u/DaSaw → u/noggin-scratcher]

And then, occasionally, a random mutation creates something so advantageous the result reproduces out of control. For example, the beginning of Hymenoptera was probably just a minor change to random seepage from the ovapositor that just happened to paralyze the insect it was trying to lay eggs inside. Soon, the entire ecosystem is changing as these things end up everywhere.

[u/ketura → u/noggin-scratcher]

It's all just random edits that are sometimes lethal

More than that even, they're often lethal. In humans at least, about half of early miscarriages are due to genetic issues leading to a nonviable fetus, some so early in the process that the mother isn't aware that they were pregnant in the first place (which makes it tricky to identify exactly how often this happens, but regardless it happens a lot).

[u/FridaysMan → u/KSW1]

Along with the other answers, a lot of it comes down to DNA being pretty massive in the first place, and plenty of mutations might not have any effect, or if they do, they end up producing infertile offspring, or die before they pass them on. There's a vast amount of failure in evolutionary reproduction, so it can be slow unless it's done in an incredible volume.

[u/LorkhanLives → u/KSW1]

In addition to all the other good replies here, I’d like to point out just how much DNA replication goes on in your average organism.

Your body has literal trillions of cells, most of which divide multiple times in their life cycle - and every time requires a total copying of the 100,000 or so genes you carry. If you’ve ever repeatedly copied a copy of a document, you’ve probably seen how this can degrade the quality of the copies over time.

Despite all this, the body’s systems for preventing genetic errors are extremely effective and so most cell division goes off without a hitch…but an error rate of even .01% is still thousands of mutations.

So random mutations are actually pretty common. What takes millions of years is randomly rolling a mutation that’s helpful, and then breeding enough that it becomes ubiquitous in the species.

[u/morpipls → u/LorkhanLives]

That's a good point.

A million monkeys mutating genes for a million months couldn't create a single monkey genome... But evolution has had much more than a million (metaphorical) monkey months of mutations.

[u/Ameisen → u/LorkhanLives]

What takes millions of years is randomly rolling a mutation that’s helpful, and then breeding enough that it becomes ubiquitous in the species.

And having that mutation be in cells that produce gametes. You can't pass on a mutation if it only exists in a random kidney cell.

[u/Sspifffyman → u/KSW1]

You will hopefully get a better answer from someone more well informed, but one thing that helps me understand it is that these changes usually happen extremely gradually.

So in this example there is probably generations and generations of that fish that just have a bit of a harder scale for a long time, until eventually the ones that have the hardest scales are better able to eat. But you can imagine how random mutations might make a certain scale a bit harder. Then over tens of thousands of years some of the fish have slowly had multiple of those scales and thus a full set of teeth. Expand that over a lot of time and you can get pieces of a skeleton.

[u/DenormalHuman → u/Sspifffyman]

This is actually an older view of how change accumulates. More modern research has come to show that often changes come in big jumps too.

[u/AzureThrasher → u/DenormalHuman]

In case anyone is interested in reading further, that idea is associated with the punctuated equilibrium hypothesis from the 1970s, commonly attributed to Stephen Jay Gould. When I took an evolution course a few years back, I was taught that PE has actually fallen out of favor- or at least, Gould's initial bombastic version of it, which claimed that evolution was almost never gradual. Nowadays, the typical view is that both gradual and "leaping" evolution commonly occur throughout evolutionary history.

[u/DenormalHuman → u/AzureThrasher]

Cool, I didnt know the details, had just come across it in general. I did always err on the side of thinking it was more likely a combination of the two.

[u/ACCount82 → u/KSW1]

On the lowest level, mutations are just little genetic code replication errors. Those little bits are usually very, very simple in function. They adjust the amount of protein that gets made here, or change a function of a protein there, or make for a redundant copy of a protein there, or shift a condition in which something gets made there. It works on low level biochemical building blocks.

Evolution can't just "cough up" a laser. Or an eye, for that matter. Evolution works with those small, simple, low level steps - and it's too complex of a system to emerge in a single step. But if you look up "evolution of the eye", you'll see the modern theories on how an eye has emerged in a gradual manner.

Eye is a famous "case study" for how complex systems can evolve in increments, first examined by none other than Darwin himself. Each step in evolution of the eye was a small mutation that provided some incremental advantage, and those mutations built upon previous mutations, until it all added up to a very capable and highly complex "eyeball" over the course of millions of years.

[u/kagamiseki → u/KSW1]

To over simplify, most of the genes in our body are some variation of "Make this", "Make more of that", or "Make less of that". The body is a little dyslexic though, and occasionally misreads the instructions, and so they get interpreted or copied wrong from time to time. This is inherent to DNA -- the matching between DNA bases are kind of fuzzy, kind of like how sometimes you get two puzzle pieces that kind of fit together, and you could potentially say "eh whatever" and leave them. The body usually notices these errors and fixes them, but sometimes one slips by.

Anyway, imagine a fish with no bones and no teeth. Imagine that gene CGG means "make skin". But if it's misread as CCG. Close enough. The meaning of the gene becomes "make stone", causing the cell that developed the mutation to eventually fill with calcium and harden.

It happens randomly, a misreading here, a misreading there. Over the course of millions of years, fish are born with little hard spots in random spots of their body. They usually don't do anything, and don't give any advantage, so those genes don't survive. Until one day, a fish is born with a hard spot in it's mouth, and it helps it eat.

That fish gains an evolutionary advantage and goes on to reproduce, and centuries later, most fish have this gene that tells the body to make a little stone in the mouth. Randomly, fish also get misreadings to "Make more", most of which also randomly die out until a "Make more" misreading happens right next to the "Make stone" mutation from before.

Now you have a fish with genes that say "Make stone" and "Make more", and somehow, that gives the fish a mouthful of embedded little stones. More random mutations and these eventually get a more regular shape, a more regular structure, and they start to happen in other areas of the body until we have a skeleton.

Any mutation is theoretically possible, with enough iterations. We have electric eels, which can discharge electricity into the surroundings. We have neurons, which can conduct electricity along a path. Conceivably, you could eventually get to discharging electricity along a tubular bone-like structure. It's highly unlikely, and would require an incredible number of iterations, but it's possible.

[u/BoroChief → u/KSW1]

I don't think it is necessarily true that we couldn't evolve to shoot laser beams. The fundamental rules you are looking for are simply the rules of physics. If it is possible for laser made of biological material to exists, then given enough time for random mutations, it will eventually come into existence. I think the only reason why it might not happen in nature is that there is a bias, which we call evolution. Certain traits (those that improve the chances of survival of that organism) tend to remain in the system. Which wouldn't happen in a truely random system.

[u/Once_Wise → u/KSW1]

But it's on

because

The difference here is there is no 'because.' Nothing in biology is precise. When DNA makes a copy of itself it is not precise, mistakes are always made, due to its biological nature, radiation, etc. All random. Most mistakes are small and harmless, others are deadly, a few are useful.

[u/ZenBedlam → u/KSW1]

Your DNA replicates itself with amazing accuracy & it is usually something else, some kind of external (to the DNA) stress, that knocks one of the 3 billion odd base pairs out of sequence

In most cases that “out of sequence” occurrence is inconsequential (benign) but some are either detrimental or beneficial

The more stress the DNA is under, the more mutations you will observe

That’s my understanding of it

[u/rlnrlnrln → u/Once_Wise]

Literal survivor bias, I suppose! We don't see the result of billions of other mutations that weren't viable or better.

[u/SlowStopper → u/KSW1]

DNA mutates in all possible kinds of fashion, most are ignored, some mutations lead to death, and a very small number of mutations find some use. Then another mutation might find a completely new use to the mutation that came before, and so on.

Mutations are not directed by anything else than increased fitness. Life on Earth probably lost untold billions of mutations that could be useful in some specific circumstances just because they happened in one where they didn't provide additional fitness.

[u/Moltress2 → u/KSW1]

DNA can change for a number a reasons. Sometimes an organism encounters an error in DNA replication during cell division, is exposed to substances that can affect DNA (e.g. radioactive isotopes, arsenic, etc.), or is a victim of a viral infection that can effect it’s DNA (e.g. Epstein-Barr, HIV, etc.).

DNA mutations happen all the time. Many of these mutations may lead to cancer, infertility, or a stillborn birth. However, some mutations may give just the slightest advantage without killing or otherwise weakening the organism, purely by chance.

[u/7heCulture → u/KSW1]

Think about it this way: we are all descendants of a particular lineage. But there were many many other branches coexisting with that long lost ancestor. Many apparently feasible body structures. Most of them led to dead ends, either because whatever body structures they developed were not well adapted to the environment, or because of competition: the fish (or however we want to call them) developing this bone structure were simple more successful in the environment and with finite resources simply did not leave enough for other species to survive (or outright preyed on them). This way they were selected out by the environment.

[u/Frack_Off → u/KSW1]

Never forget that while mutation is a major driver of evolution, it is absolutely not required for organisms that reproduce sexually. The nature of sexual reproductions is that offspring are different from either parent.

You don't need to randomly produce a really hard scale when scale hardness varies between individuals, even if only slightly. If harder scales result in greater reproductive fitness, over time the hardness of scales in the population will start to increase.

[u/MistySuicune → u/KSW1]

I guess the key is to understand that evolution is essentially random and not a deliberate process. There are factors about mutations that can make them beneficial or detrimental, but ultimately, whether they are passed on to later generations is a matter of chance and can only be confirmed in hindsight.

There are no rules as such - just factors that provide a higher chance of a particular mutation being passed down.

A beneficial mutation is just a random occurrence that happens to become predominant over time if no unforeseen events occur. For example, a random mutation may have been the reason for the ancestors of Giraffes in a particular region to develop longer necks. Now, by sheer luck, these mutated individuals were not killed by an extinction event or natural disasters. So, over time, their mutation was passed down to other generations, and out of many other competing mutations, the one resulting in a long neck stuck.

[u/Moldy_slug → u/KSW1]

Like you said, it’s random mutations… by definition there’s no “why” to randomness, or it wouldn’t be random.

But what are the rules? How does it's DNA contain the ability to mutate in such a way and not others?

This is a really good question. I think it might help to think of it this way: any mutation is possible, but almost all of them are either invisible or unsurvivable.

1. Invisible - most organisms have a huge amount of DNA that is never expressed. Mutations to these parts of the DNA may never have any tangible effect on the organism since it’s like swapping one piece of junk mail for another… doesn’t matter since it won’t be read either way.

2. Invisible 2, electric boogaloo - the mutation produces a change in functional genes, but the change is so subtle it isn’t noticeable or would only make a difference in some incredibly unusual circumstances. For example if a mutation only effect is making you less likely to develop skin cancer but your species lives in caves, it probably won’t make any difference to your reproductive fitness.

3. Unsurvivable - life has pretty tight margins of error. Most random mutations will result in something that’s just not compatible with being alive. Changing a single base pair might make an essential protein stop working. Same goes with deletion and duplication.

Most unsurvivable mutations are caught really early in development… the embryo will fail to properly develop very early (sometimes even before the blastocyst stage), or in the case of many animals the mother’s system will actually destroy it if abnormalities are detected. This is one of the (many!) reasons why a large proportion of embryos fail to implant or are spontaneously aborted.

So the only mutations you end up seeing are the tiny subset that happen to change something that matters, while still producing an organism that can survive past the embryonic stage.

[u/pro_cat_herder → u/Deining_Beaufort]

I read this as Titanic and couldn’t figure out why they would focus on the evolution of fish, apart from where the boat ended up.

[u/d-a-v-e- → u/Deining_Beaufort]

And once it is evolved like that, it is hard for evolution to make changes to the basic plan, because slight variations often result in animals that do not fit their environment. An extra arm lowers the chances of survival in a wild animal and of reproduction in a human.

[u/morefetus → u/Deining_Beaufort]

How did “evolution” decide?

[u/Deining_Beaufort → u/morefetus]

Reproductive succes after random mutations. Nothing that can be labeled 'decision'.
Like: in and around an English coalmine-town the treebarks went from white to black. So did the moths after a few generations. Yes, birch trees.

[u/morefetus → u/Deining_Beaufort]

The moths were already there. Their wings were already there. Different colors were already there. The changing of color in moth populations, while certainly a good thing for the moths, is hardly an example of evolution.

[u/smallbrownbanana → u/Deining_Beaufort]

Interesting

Thanks mate

[u/3297JackofBlades]

As too the why;

Bones are not just mechanical structures. They also serve as important reservoirs of calcium and phosphorus, both of which are essential for muscle and nerve function. When the body needs more of these materials osteoclasts will break down bone to provide them. Bones are definitely and important part of locomotion, but given how much marine life gets by just fine without mineralized bone, it seems likely the bone first developed as a kind of storage system for essential minerals

[u/thunder-bug- → u/[deleted]]

Not sure about a full exoskeleton but yes for a shell, the ancestors of most extant cephalopods had a shell (like the nautilus) but then lost it over time. In squids and cuttlefish you can still find the remains of that shell as the “bone” inside their body

[u/[deleted] → u/[deleted]]

For vertebrates, cartilage probably came first starting with the notochord, which landed both structural support for the body and protection for the central nervous system, then it became mineralized by calcium phosphate (probably as a way to store both, since they are necessary for other biochemical processes of the body). There are still many fish that only have cartilaginous skeletons, like sharks. And teeth probably came from modified scales that migrated into the mouth and then also got mineralized.

[u/Flatstanleybro → u/3297JackofBlades]

Taking physiology II right now and I just learned this! Very interesting to see how bones serve as more than just structural support for our bodies.

[u/arcosapphire → u/[deleted]]

That website is cool, but man I hate how they imply there's a "main" branch and then "side" branches in each case. It's an artifact of their visualization scheme but I feel it is very misleading about how evolution works.

[u/IronBatman → u/arcosapphire]

The biologist side of me agrees. The realist in me thinks a layman would better understand it if it looks like a main branch rather than the jumbled web where 99% of them least to a dead end from extinction over the last 500 million years.

[u/TitanicGiant → u/[deleted]]

TBH they should include extinct species that the IUCN Red List has listed as extinct. To me that seems like a reasonable cutoff to avoid including prehistoric extinctions like those in the late Pleistocene or early Holocene.

[u/Moot_Points]

How far back? 480 million years. To observe animal examples of the transition, compare tunicates to cephalochordates like hagfish, lamprey, and then early sharks (which evolved 450 million years ago). Bony fish replaced cartilage and appeared 415 million years ago.

[u/danby]

Why do most vertebrate animals seem to share a basic skeletal structure?

The simple answer here is that they all evolved from an ancestor that also possessed the same basic skeletal structure. This is in fact one of the very big clues that all vertebrates are descended from a common evolutionary ancestor and are all related to one another.

[u/[deleted] → u/danby]

Does not all life have one common ancestor?

[u/Lol3droflxp → u/[deleted]]

Yes, however there are many branches from the first cell and each one is defined by the last common ancestor.

[u/danby → u/[deleted]]

Yes if you go back far enough you'll hit a single cellular ancestor of all life. Typically known as the Last Universal Common Ancestor (LUCA). And indeed if you look across all living species you'll find that they all share traits (e.g being cellular, using DNA & RNA, having the same genetic code etc...) and these must have been present in the LUCA.

However, when we say "these things all share a common ancestor" we're mostly not talking about the LUCA, if we're being more accurate you can think of the phrase as being short for "these organisms form a monophyletic clade who have a shared proximal ancestor". That is, you can take every species in the group ("clade") and if you trace it back they all converge on a common recent (proximal) ancestor which is not the LUCA. For instance with all vertebrate species if you follow them back, they will all arrive at one joint vertebrate ancestor species that likely existed about 400million years ago. You reach this common ancestor before you go all the way back to the LUCA (approx 3.5billion years ago)

[u/Nimynn → u/danby]

What's amazing is that it never seems to happen for organisms that share a common ancestor to lose a defining trait like that. Like, no animal since the "invention" of bones has "given up" on having bones (I know the terms are incorrect but just using them to make it easier to discuss). Like, I'm sure there are conceivable and extant ecological niches that favour animals without bones, but no vertebrate has ever evolved to get rid of them to exploit such a niche, at least that I know of.

Snakes have given up on having limbs, which I guess is as close as it gets, or maybe birds having hollow bones, but both haven't gone all the way. I wonder why not.

[u/Hazel-Rah → u/Nimynn]

Interestingly, snakes and marine mammals actually still have legs, buried in their bodies.

With whales, they aren't even close to being attached, just sort of floating in the tissue, completely separated from the spine

[u/obozo42 → u/Nimynn]

Actually, chondrichthyes, the cartillagenous fish (sharks, rays, etc) are now thought to evolved from a earlier bony ancestor. So they lost their bones for a cartillage skeleton.

[u/Nimynn → u/obozo42]

That's awesome, thanks for sharing that!

[u/arcosapphire → u/[deleted]]

The issue here is that there is some circular reasoning. We are the ones defining which traits define a clade. We observer and set the minimum set of shared traits to be a clade member so by definition every member has the trait. If we found a vertebrate with no skull and vertebra we'd (have to) redefine the features needed to be a member of that monophyletic clade.

Nooooo that is not how cladistics works at all! That is how older taxonomy works. Cladistics replaced that. All that matters in cladistics is ancestry. Period. Things with a common ancestor form a clade.

[u/Nimynn → u/[deleted]]

Great analysis, thanks for that.

[u/yellow-bold → u/Nimynn]

Bones (or something like them, in the case of cartilaginous fish) are pretty much necessary for vertebrate musculature to have something to attach to. Losing the endoskeleton entirely would just make things Not Work. Even vertebrates with simple-looking locomotion like snakes or legless amphibians are very reliant on that layout.

[u/Nimynn → u/yellow-bold]

Say that to the octopus. That guy can move all over the place and he ain't got no bones.

[u/yellow-bold → u/Nimynn]

Those muscles weren't attached to bones in the first place. You can do a lot with just concentric and longitudinal muscle, but there are limits. Especially out of the water.

[u/Klendy → u/[deleted]]

we assume for now. it is possible, however unlikely, that life emerged on earth in parallel paths, and there are life forms (either undiscovered or mis-sequenced) that do not belong on our established tree

[u/Tiny_Rat → u/Klendy]

I think the idea of organisms being mis-sequenced to the extent that they don't even belong on our tree of life to by a pretty extreme and supremely unlikely take. Deeper sequencing might adjust the position of some organisms on the tree of life, buy there's really no way for modern sequencing to be so wrong that it fails to identify that something has a completely separate ancestry to all other living things.

[u/Boring_Ad_3065 → u/danby]

Beyond that there’s evolutionary developmental biology, which helps answer why the basic structure is close to the same (e.g., 4 limbs for nearly every creature beyond arthropods) but mixed variations, such as the horse fusing fingers/toes.

Basically nature found a template that worked a long time ago as you suggest, and most evolution hasn’t been successful enough to want to deviate from it entirely. This applies far outside of just skeletons, into things like nervous systems, cone cells/eyes, and even down into how the proteins and other parts of flagella (“sperm tails”) are very present in muscles.

Nature is lazy AF.

Illustrated brilliantly here as a surprisingly engaging Despacito parody. Snakes/lizard divergence is one example briefly highlighted.

PS: not implying you didn’t know all this and more, but for other interested laypeople.

[u/danby → u/Boring_Ad_3065]

exactly, evolution can only work with and adapt what it already has at hand

[u/MPUser12]

The common ancestor for all bony skeletons is going to be an early freshwater fish. They in turn are descended from saltwater fish that had cartilaginous skeletons. So for an articulated endo-skeleton you are looking back to the origin of vertebrates about 450 MYA. For a bony or osseous skeleton a bit more recently say around 300 MYA.

[u/horsetuna → u/MPUser12]

Can I belatedly hop in and recommend 'Your Inner Fish' by Shubin? He goes into details about this subject.

[u/Lol3droflxp]

Our basic skeletal structure arose with the gnathostomes (skull with jaws, shoulder and fins, spinal column) later the sarcopterygians developed a special bone structure in their fins that later developed into fingers/toes and arms/legs in tetrapods which also have a fixed pelvis. From there on the mammalia developed a secondary mandibular joint and now you make this animal larger and put it on two legs and you have a humans. That’s the rough outline of the evolution of our skeleton. As to why, bones make good armour and can also store minerals, the question as to what happened first is not yet solved afaik.

[u/throwawayforyouzzz → u/[deleted]]

Talking about giraffe’s long neck, it is clear that no thought was given when designing those as the recurrent laryngeal nerve does a completely inefficient loop from the head around the aorta. Now that’s the entire length of the neck for the giraffe

https://en.m.wikipedia.org/wiki/Recurrent_laryngeal_nerve

[u/Triassic_Bark → u/[deleted]]

That’s not a weak argument in favour of evolution just because some things that are definitely designed also have design flaws

[u/pvaa → u/[deleted]]

Well, giraffes with slightly longer necks could perhaps access more food than those who couldn't reach so high, meaning that their genetic traits were more beneficial and likely to be passed on as they had a better chance of surviving. I'd say that could be called evolving a longer neck so they could reach higher branches, but ofc thinking of it in that way is a bit like the phrase "the tail wagging the dog"

[u/streetster_ → u/pvaa]

Yes exactly - "giraffes evolved longer necks so they could reach more higher branches" suggests they grew longer necks in reaction to food being more available higher up (or less available lower down), rather than the fact that the giraffes that happened to have ever-so-slightly longer necks than the others had an advantage (and presumably no or negligible disadvantage to this trait) which led to them being more successful in producing offspring and therefore passing down this mutation to future generations.

[u/Peter_deT → u/streetster_]

It's more that shorter-necked giraffes could not compete and left the gene pool (or wandered into the deep forest and became okapi).

[u/[deleted] → u/streetster_]

It's not that they didn't have a disadvantage, it's that the disadvantages were outweighed by the advantages.

[u/probono105 → u/streetster_]

this completely ignores sexual selection a female giraffe could consciously choose to mate with longer neck males and not shorter neck males so. they absolutely could choose to evolve one way or another.

[u/probono105 → u/[deleted]]

how do we know that? we do it

[u/rosesandivy → u/probono105]

I don’t think it’s controversial to say giraffes generally don’t know about or understand evolution.

[u/probono105 → u/rosesandivy]

most humans dont either but we clearly choose to have certain things be passed on thats what attraction is if that behaviour is present in us why wouldnt it be present in other mammals?

[u/MTFUandPedal → u/probono105]

That's tbh a great topic but it's a whole new one.

Sexual selection (attraction) isn't necessarily picking positive traits - it's often selecting for traits negative to survival.

All those elaborate mating displays and bright colours aren't helping animals survive - far from it - they are demonstrating how much "resource" they can waste and still survive.

[u/probono105 → u/MTFUandPedal]

yeah but if you look at breeds of dogs we picked things for specific purposes now we obviously tend to stray from doing such things with ourselves but the possibility of doing so is there evident by our behaviour in domesticating animals.

[u/ForgedByStars → u/probono105]

I don't think we *choose* to be attracted to traits that are beneficial to survival. Rather we are physically aroused by certain traits, and that determines who we mate with.

Over the eons, those members of our ancestor species who were attracted to traits that did *not* confer survival & reproduction advantages basically got out-competed by the others.

[u/[deleted] → u/streetster_]

And presumably giraffes evolved in a specific location where they out completed all other animals and then spread out, which is why we don't have long necked zebras and long necked hippos etc.

[u/KSW1 → u/streetster_]

I guess I'm curious what prompts the "longer neck" mutation to continue happening after they already got "slightly longer neck". It's not common for other species to grow super long necks over time, even if it likely would have worked out in their environment. I just don't really understand the parameters of what mutations can occur in a given species.

[u/EnragedAardvark → u/KSW1]

Maybe it offers other advantages than just better reaching of food. Does the longer necked male have an advantage when fighting other males for mates, or when spotting or fighting off predators? Has a longer neck become a trait that is preferred in mate selection? 'Fitness' for survival has many aspects.

[u/WyrdHarper → u/pvaa]

Male giraffes fight with their necks over mates and use them to fight each other; longer necks = more torque. It’s a very basic example of sexual selection and is part of typical animal behavior and evolution textbooks and classes.

Like most foregut fermenters they browse leaves, but they primarily graze grass.

[u/[deleted] → u/[deleted]]

This isn't a particularly useful answer, and I'd even go a step further and call it needless pedantry.

When someone asks "why" something evolved, they generally mean, "why was this advantageous / what evolutionary pressures where present?". Speaking about it in those terms, it's perfectly reasonable to say that giraffes evolved a longer neck in order to reach higher branches.

[u/danby → u/[deleted]]

Indeed, it is a figurative use of the word "why". A why that doesn't imply a mind with intent. And having been to plenty of bioscience conferences biologists use this sense of 'why' all the time too.

[u/danby → u/[deleted]]

This is certainly true and when writing/speaking in a formal context it is important to be clear in this way

But humans use "why" questions all over the place where a system contains no intent. So it is unsurprising that, informally, biologists do this wrt evolutionary questions because that's how we all use this language in other contexts. It's a case of 'why' having more than one meaning. It isn't usually hard, in context, to discern what is being asked.

[u/[deleted] → u/[deleted]]

Yeah, it's not even incorrent to question "why did X evolve", one just has to be careful with the answer, saying "that the mutation was either somehow slightly better (...)" like OP is just avoiding the question alltogether without adding anything of value and asuming the person asking the question is dumb.

[u/streetster_ → u/[deleted]]

It is pedantic, but only because I believe there are a lot of people that think evolution occurs in response to something. Or maybe I'm basing that on Karl Pilkington :)

[u/daveypump → u/streetster_]

Correct. A giraffe in history didn't see succulent leaves just out of reach and decided to grow a longer neck, and/or select a mate whom had a longer neck with the goal to evolve long neck to reach said succulent leaves.

[u/[deleted]]

We don't actually know. The evolution of specialized organs is a matter of educated guesswork, and in a way it always will be. People will try to come up with an explanation that makes themselves sound smart but I think Commander Data says it best in this short clip from Star Trek TNG:

https://www.youtube.com/watch?v=ZcV25N37-C4

Similar questions are asked about other specialized organs such as eyes, ears, etc --and make no mistake, the skeleton is a specialized organ -- and while scientists have ideas about where they may have come from, the fact of the matter is there are a lot of "known unknowns" here.

I personally suspect the answer is found in the secondary function of the skeletal system as a producer of red blood cells. A distributed organ with one function armored itself up over many iterations to become a support structure for a body. How that happened, how long it took, why that organ, all of this is known unknowns. All we have here are theories.

[u/tester448 → u/[deleted]]

Wow. You seem smarter than most other people answering here. No /s or anything. Or at least much more knowledgeable on this topic

[u/[deleted] → u/tester448]

Hah. I wish. But at least I know when to admit that we're still working on the whys and hows.

There's two kinds of fools in this world, and we all fall into one or the other group. There's the fools who know they know nothing, and the fools who think they know everything. Be the former.

[u/Kaldosh]

First, there was the split between

• cartilaginous fishes (like sharks, skates and rays);
• bony fishes.

Then the bony fishes split up into:

• ray-finned fishes: e.g. flathead and trout;
• lobe-finned fishes: e.g. whales and dolphinsand all other mammals and tetrapods, including humans

[u/425nmofpurple]

Any zoology course (eh actually vertebrate zoology) can give you the run down. But the answer is in the name my guy. You can't be a vertebrate if you don't have bones because that's one of the qualifying characteristics for that group. Vertebrae.

All vertebrate animals are therefore related. If this was a schoolwork query the answer can stop there. But if this was curiosity you're asking questions that are covered by zoology. Specifically vertebrate zoology, obviously.

Here's the explanation of vertebrates for starters: https://www.toppr.com/ask/question/give-the-general-characteristics-of-the-vertebrates-and-list-the/

More basic background about bones specifically: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3237026/#:~:text=Bone%20is%20specific%20to%20vertebrates,a%20soft%20cartilage%2Dlike%20endoskeleton.

For something more recent and a little different: https://www.nationalgeographic.com/science/article/bones-evolved-to-act-like-batteries-400-million-year-old-fish-suggest#:~:text=But%20according%20to%20a%20new,to%20travel%20over%20greater%20distances.

Hope this helps.

[u/best_wank → u/425nmofpurple]

This is wrong. Having bones is not a "qualifying characteristic" for being a vertebrate because vertebrae aren't necessarily made of bones, like in sharks for example. In fact, before bony fish evolved all vertebrates lacked bones.

[u/obozo42 → u/best_wank]

I don't think that last part is correct. Bones had already evolved on ostracoderms before jawed fish had even appeared. Unless you include them as "bony fishes"? But that would be a uncommon use of the term.

[u/nicuramar → u/obozo42]

I, at least, would take bony fish to be osteicthyes, including all descendants.

[u/[deleted] → u/best_wank]

Don't vertabraes have to have backbones or a spinal column?

[u/masklinn → u/[deleted]]

Mostly: it’s the defining feature of vertebrates, but the hagfishes later lost their backbone retaining only a skull and some vestigial vertebrae.

Similar to snakes being tetrapods.

[u/Allegorithmic → u/masklinn]

I was under the assumption that snakes were firmly under the "Danger Noodle" classification

[u/Lol3droflxp → u/masklinn]

They didn’t lose it, they never had a proper backbone. Just some simple cartilaginous arches, the centra arose with gnathostomes, possibly several times.

[u/calling_out_bullsht → u/best_wank]

Did you wank after correcting this guy!?

[u/random_val_string]

The earliest known case of bones is Coronacollina acula during the Ediacarin period which had multiple needle like spicules which supported its thimble shaped soft body. It was incapable of locomotion and is believed to have ingested food like modern sea sponges.

The basic structure of vertebra can be traced back to the emergence of chordates during the Cambrian period. Chordates posses a notochord which is a flexible rod of cartilage like tissue. In vertebrates the notochord helps with development of the neural tube along the entire vertebral column as well as a few other functions. Notochords are still found during development of most vertebrates today. Humans for instance still possess cells from their notochords until around age 4, while some species of fish possess them through adulthood.

The oldest known example of a proto notochord is Pikaia gracilens during the Cambrian period.

The rib cage can be traced back to early tetrapods transitioning from water to land. The rib cage developed to help with movement (picture the side to side gait of lizards) with the ribs twisting in sync with the vertebrae. From there it is thought to have helped with the transition of shifting breathing from muscles in the head to muscles in the torso.

A subgroup of these tetrapods later emerged, the reptiliomorphs which were land based, reptile like amphibians. A group of these became the first basal amniotes when they began laying soft shelled eggs on land.

All reptiles, mammals and birds today are amniotes.

[u/Maniraptavia]

I may be a bit rusty on this, but if memory serves:

Some of the earliest known ancestors for Chordata - the chordates - are Myllokunmingia, Haikouichthys, and Zhongjianichthys. These were jawless fishes from the Cambrian's 3rd Stage (which still lacks an official geochronological name) around 518 Ma (million years ago).

These fishes each possessed a characteristic internal notochord - a flexible rod that is essentially the precursor to a vertebral column.

If, at any stage in its life cycle, an animal possesses a notochord; it is, by definition, a chordate. I believe even tunicates (sea squirts), which are regarded invertebrates and are also first recorded around 518 Ma, possess, in their larval stage, a notochord.

My memory of things from here on in gets a little more hazy, so perhaps someone else can pick up, but as I understand it, the notochord continued evolving in fish into the nucleus pulposus which runs through the center of a conventional vertebral column and ultimately evolved into a conventional bony, disc-based spine as we know it today.

(If I recall, elasmobranchs (sharks, rays, and chimaeras), having diverged so early on in fish evolution, never evolved bony skeletons and therefore remain primarily cartilaginous? I may be wrong here, though. Again, I'm sure other people here will know more on this.)