From "the social function of intellect"[1]:
"Henry Ford, it is said, commissioned a survey of the car scrap yards of America to find out if there were parts of the Model T Ford which never failed. His inspectors came back with reports of almost every kind of breakdown: axles, brakes, pistons - all were liable to go wrong. But they drew attention to one notable exception, the kingpins of the scrapped cars invariably had years of life left in them. With ruthless logic Ford concluded that the kingpins on the Model T were too good for their job and ordered that in future they should be made to an inferior specification. Nature is surely at least as careful an economist as Henry Ford. It is not her habit to tolerate needless extravagance in the animals on her production lines: superfluous capacity is trimmed back, new capacity added only as and when it is needed"
> It is not her habit to tolerate needless extravagance in the animals on her production lines: superfluous capacity is trimmed back, new capacity added only as and when it is needed
It's not exactly wrong, but it's way too anthropomorphic and attributes way too much intent.
Plus there's plenty of natural stuff which at least looks way over-engineered or redundant/unnecessary in its current form. The Mantis Shrimp's eyes for instance. The gallbladder also seems mostly redundant, and while one can argue that the lobed paired design of lungs is necessary considering the common occurrence of respiratory diseases redundant kidneys seem less than necessary.
I'll keep my paired lungs. Had one spontaneously collapse about 10 years ago, and had there not been a second in it's own pleural cavity, it would've been a much worse time for me.
As an aside, one really cool thing that happens in the case of a collapsed lung, is the trachea will shift toward the healthy side under less pressure. Called a tracheal deviation https://en.wikipedia.org/wiki/Tracheal_deviation
Nature can’t (or at least has a very hard time) climb out of the local minima it has created.
The gallbladder has a heap of design flaws but it is quite useful (until it causes problems). Bird lungs would be much more efficient a design as they don’t have dead space in the way ours do. And having 2 of an organ has more to do with our bilateral body symmetry which was an early evolutionary choice of our line than anything else
>It's not exactly wrong, but it's way too anthropomorphic and attributes way too much intent.
This made me start wondering something... at what point can something be attributed to intent? When did the first intent arise? If humans are blobs of matter following the laws of physics, why can we possess intent when nature cannot? What is the simplest process which can have intent?
This is probably just a restatement of an existing problem like where does intelligence come from. Just a random though I had reading your post.
People (geeks often) attribute efficiency to evolution's designs. The process really produces just barely good-enough for given environmental pressures/problem domain. Nature is the queen of avoiding pre-optimization and YAGNI.
Which begs the question, since humans have been able to dominate their ecology and competitors to such a massive degree, why didn't our evolution stagnate a long long time ago? The answer, as far as I have read, seems to be that for humans, competition within the species (for sexual opportunities, position in the dominance hierarchy, etc) has been the primary driving force pushing our brains to evolve to the size it is today.
If I could have a team of millions of developers spending centuries building applications then I too could work out the leanest possible implementation.
Nature makes a lot of pull requests, but has a great peer review system that prevents bad design entering the core of the system.
nature produces the optimal animals for survival, and its not limited to the current form the animal is in. (I'll get to that later). think of this as a machine learning problem, you want to have regularization penalties from over-fitting the environment, because it will inevitably change.
the author makes some absurd comments. "There doesn't seem to be any fundamental reason why an animal couldn't evolve which makes steel, for example. It would get its raw material like we do, from iron ore."
how does the author expect our bodies to produce heat in the thousands of degrees to burn out the impurities in iron and infuse carbon in its super heated state? i dont buy their argument that our bodies can make anything just because its building stuff at the molecular level. humans survived a lot of extinction level events, a lot of global famine. even if we could do the former, we might have gone extinct if we had extraordinary dietary requirements of iron. and what ever animal we evolved from would have also had to deal with that, and they experienced even larger extinction level events.
i was thinking about why the dinosaurs had such small brains. other animals and reptiles living today existed in the same period, and they had larger brains, so I thought the dinosaur brains were small by design, why?
i think because being big was adventitious, and being egg layers, only so much air can travel through a membrane. some eggs were as large as 2 feet long, probably not a lot of air getting into the whole system, so a hulking brain is a waste. even if they had small eggs, they needed the ability to evolve / or activate genes to grow big when allowed to do so.
Bone is an organ with multiple functions beyond structural support. It creates a reservoir for calcium and phosphate homeostasis and of course contains bone marrow. It also has attachments for muscles and connective tissue, and adapts to environmental conditions (eg see a tennis player's forearm). A titanium bone could do none of these things. The question should really be why are bones not reinforced with metal or metal composites. In general if greater strength is needed it can be achieved with thicker bone, which has a far lower evolutionary barrier than eg metal composite bones. Additionally, the material properties of the whole biomechanical apparatus need to be considered. A super strong skinny thigh bone isn't much good if the area available for ligamentous attachment is so small that the tendons keep tearing. Most injuries involve connective tissue and muscle rather than bone.
Not to mention the role of bone in blood cell synthesis!
The bone is a fascinating organ and sadly misunderstood by most people. They are, essentially, living rocks. Our bones are innervated, full of living cells, and constantly engaging in a chemical equilibrium with the body on CaPO4 as you point out.
Furthermore, the bone needs to grow along with the creature. It has to be soft enough to accommodate childbirth but allow growth and hardening as the organism matures. The process by which this occurs in natural bone is complex and remarkable.
I think what people mean when they say "reinforced with metal" is "reinforced with substances in metallic form".
From that point of charity we can start to say things like "Organic environments cause corrosion in commonly-available pure metals", or "Pure metals can be toxic to animal cells in large amounts".
Reminds me of The 6 Million Dollar Man. His super strength bionic limbs would have just torn the rest of his body apart. Strength has to be in balance with the rest of the body.
Extra functions of the bones cannot explain fully his question.
If it is possible to for the body to synthesize whatever material, it can create a frame for the bones, then wrap that frame in bio-active layers. Basically, a skeleton for the skeleton. Given the intricacies of other body organs (think the sizes and complexity of the eyes, says), such is not too hard of the task.
In fact, this probably answers all other concerns raised here. Corrosion and electric-conductive? A bio-compatible wrap (similar to enameled steel) solves that. Grinding between different bones? The ends of the bone can be built out of different material than the fragile length.
Furthermore, none of these concerns matter for, says, horns, especially the tips. Evolutionary speaking, it makes complete sense for animal to evolve steel-tipped horns: these steel parts hurt no one but their enemies.
(also note, carbon fiber avoids a lot of these bio compatibility issues).
In other words, animal kingdom did not have metal parts because synthesis is impossible, rather than because of disadvantages of metals per se.
> Evolutionary speaking, it makes complete sense for animal to evolve steel-tipped horns: these steel parts hurt no one but their enemies.
Lightning might be an important consideration here. An animal's chances of getting zapped would go up significantly if they were waving around metallic horns in a storm.
Good point, although there could be some strands of metallica alloy through the bone matrix to reinforce it, breaking your bones is so rare for most people, it's no surprise nature spent budget on other places.
It's sometimes underestimated at what level of detail evolution operates.
Consider this: there must have been quite a lot of prehistoric humans who died, or otherwise suffered reproductive failure, because they lacked eyebrows.
Breaking major bones, especially in times before modern medicine, was without a doubt a life-threatening event. And considering the prevalence of fractures today, with our largely sedentary lives, it must have happened fairly often
Surprised that this totally blows past the chemical reasons why not. There's an excellent answer by shigeta on the Biology Stack Exchange[1] to this very question.
His major answers are that electrical conductivity is likely to be a huge problem for the nervous system, and that iron and aluminum readily oxidize (aka rust). Iron oxidization is useful in hemoglobin but would be problematic in your bones, and while a body could be designed with conductivity in mind, it would at minimum also take a reworking the nervous system.
What you pointed out is a very astute answer, but comes from a creationist perspective rather than an evolutionary perspective. His main answer is:
> Firstly, fully reduced (oxidation state 0) metal has a high energetic cost to create in reduced form.
Basically, it takes a ton of energy to make steel. We are literally burning gigagallons of over a billions years worth of pressurized organic matter to have made all of the steel we have made in the past century and a half or so. We could make a super inaccurate but somewhat plausible estimation that we have used something like 150 million years worth of the entire earth's lifeforms at the time's dead bodies and converted that into 150 years worth of steel. So if my orders of magnitude are correct...it would be something like a million times more difficult energy-wise for an organisms to create steel from scratch than calcium-based hardened material.
That's assuming we have burned through 15% of a billion years worth of oil from bacteria, that 100% of the bacteria converted into oil and then converted directly into steel, and that there was only a billion years of bacteria to oil creation. I am sure these numbers are off, but maybe that means it's only 100,000 times or 10 million times more difficult for organisms to make steel rather than bones.
You are vastly overestimating the efficiency of turning life into oil, and vastly overestimating how much has gone into steel. The article even addresses the energy needed to reduce iron, and it's not that much. The high number of 60kJ/mole/reduction comes out at about 500 food calories per kg to reduce twice. Industrial molten iron production is only around 5000 food calories per kg. So it's really no big deal to produce a few kilograms per lifetime. (Mixing in other elements to get steel is a minor cost per kg.)
Well that's interesting, it seems we've got the next few centuries to start colonizing the solar system, or we're going to go extinct at this rate of usage... Who was it that made the theory, a next civilization may never happen because we used up all the easily available resources...
For one, the pins are small and hopefully don't touch nerves. More to the point, Titanium:
— Is nontoxic.
— Is biocompatible, and can semi-integrate into bones, a process called osseointegration[1], which makes for much better implants.
— Isn't ferromagnetic, so you can use MRI to examine and maintain implants safely.
— Is less conductive than many other metals.
Another problem is breaking/remaking these metal bones. Biomineral structures can be reformed - bones break mechanically, and have to be repaired. While biomineralization is mentioned, I'm not sure how easy it would be to 'digest' pure metal in order to repair it.
He talked about that in the article. His point being that metal bones would be effectively indestructible for typical loads placed on them by organisms and if they ever received damage, they would bend instead of break.
I'm not sure if conductivity matters. Bodily fluids are also conductive, yet don't seem to interfere.
More importantly, neurons use ion gradients across their membranes to conduct signals. It's not electrons flowing along, as it is for wires.
While the magnetic field created by thousands of neurons firing in concert can be picked up using wires (EEG, ECG), and neurons can be induced to fire with electric shocks, I actually doubt anything would happen if you were to connect two neurons by wire.
At the very least, the wires would need to have contact with the axons (neuron terminals). A neuron can be a meter long, but it is isolated by a fatty membrane along its body.
The article addresses that, albeit with some hand-waving:
> The activation energies for oxidation and reduction of iron are of the order of 30-60KJ/mole, comparable to the figure of 57KJ/mole for ATP, a molecule which is commonly used for delivering energy around our bodies. We normally make iron from its ore at very high temperatures, because the rate-limiting process is diffusion in the solid state. But the body makes materials in a very different way, from the bottom up, atom by atom, molecule by molecule. And of course the fact is that you are already oxidizing and reducing iron inside your body all the time.
>> But if you had metal bones they wouldn't ever need repairing: titanium alloy for example has a fatigue strength of about 500MPa which is more than five times greater than the stresses that it would experience in its life as a bone.
It's worth remembering that Calcium (the substance bones are made of) is, in fact, a metal [1]. And our bodies have no problem growing and repairing our bones. Why wouldn't that happen with steel?
Also- the bit about the stresses that a titanium alloy bone would experience in its lifetime- yeah, that, probably. We probably have bones as tough as they need to be, or _needed_ to be in the last million or so years.
________________
[1] A factoid that my 16 year-old self, obsessed with Metal (the music) found deeply satisfying. "Dude, my bones are made of METAL".
The calcium in bones is pretty much all in the form of calcium phosphate, which behaves very differently from a pure metal, e.g. with respect to conductivity. Saying that bones are made of metal is a bit like saying that stone is made of metal.
I would hazard a guess that necessary reactions involving calcium require (a lot) less temperature than those that would be necessary to build a bone-like structure out of iron or aluminium.
That's because neither you nor anything in your diet (nor anything in your diet's diet) has titanium teeth and jaws.
The Earth's crust is 3.6% calcium, and we get more than enough of that in our diet...it's 5% iron. There's even a lot of titanium - fully 0.6%, much higher than 'rare' elements like carbon! [0]
I don't think we'd have any trouble getting it if the metabolic and biological systems that are employed to get us calcium were instead employed to produce titanium.
"...why have our bodies, and those of other animals, evolved so as to make the particular structural materials that they do make, and not to make others, especially metals..."
Because that's what's good enough to get through the crucible of successful genome transmission? Evolution doesn't have an end goal; every "improvement" came about by random changes, either in the genome or in the environment, which yielded a reproductive advantage to some new gene or genes. I'm not sure if the author intended it but this seems to fall into the common fallacy of believing that evolution is an active process guiding organism toward some optimal state. Organisms don't evolve "to do" anything. They end up there. Contemporary genomes are what's left after everything else has died. Not the conquerors of mountains.
Evolution is one of the hardest things to actually fully integrate into a mental model. There are so many subtleties that just do not interact well with our tendency to ascribe motivation to stuff.
It seems fairly intuitive to me. Think of a bunch of marbles falling through a series of nets. Changes in a particular marble, or in a particular net, might let the marble fall through. Marbles that fall through one net get to try again with the next net. Evolution just means comparing marbles that collect in each net. There's a million answers to the question "how can a marble get through this net", and the nets don't care if anything gets through at all.
Then there is also the evolutionist's reply to this question: because the ocean has a lot more calcium than iron, (in ppm Ca: 400, Fe: 0.003[1]). So all the evolved mechanisms from shells to (cuddle) bone were in place due to available materials long before any other possibility presented itself.
Also from an engineering standpoint, I would think that just metal-izing the skeleton wouldn't be very helpful. You'd just switch to breaking all of the tendons and ligaments and other connective tissue first instead. So you'd need to strengthen those up too, and in a way that is still as durable and repairable.
Then all of this stuff is adding more weight, we're going to need bigger or more powerful muscles to move it around well. Then we'll need bigger/better heart, lungs, circulatory system to fuel that extra muscle power, and improved digestive system to get more energy for that stuff into the body. Skin is seeming kinda fragile with all of this extra bone strength and muscle power, better toughen that up too.
I think I have wondered far more often why bones aren't made from a substance stiff enough to act as anchor points for tendons, but also flexible enough to bend over and then snap back to its original shape without breaking. The bending stiffness and yield strength seem very important for the types of stresses on a biological organism.
So why aren't our bones made out of polyimide-polyamide-fiberglass composite?
I don't know enough biology to be sure, but I'm pretty sure that some of our ribs are fairly flexible in this way. I would guess, if we had to come up with a reason why those bones are flexible and our arms and legs, say, aren't, it's that the tradeoff in ability to exert large forces in a predictable way and taking bigger impacts before breaking isn't worth it.
Not that evolution is able to actively design things in that way, of course. More like it was an evolutionary advantage for those ribs to be flexible, but any flexibility in arm and leg bones and other major bones was not an advantage.
Evolution is also an optimization engine. Living creatures are not over-engineered because doing so requires additional resources, and resources are limited. Creatures that are not over-engineered are "fitter".
For example: during a famine, perhaps a growing child with "normal" bones is much more likely to survive than a steel-boned counterpart who is unable to find the required extra iron ore and energy needed to grow.
I know this is pretty much a nerdy tangent, but something similar is discussed often in Star Trek with the Klingon anatomy. Supposedly every major organ has a redundancy (though I'm not sure they really mean EVERY organ). It's seen as a strategic advantage by many for beings who live a violent lifestyle, but some question it as over-engineering. With twice the organs there's the potential for twice as many things to go wrong during a normal lifespan.
If you consider the fact that human males who live to 80 have a 80% chance of prostate cancer (IRL not Star Trek), it seems like we live with time-bombs that do eventually go off.
Did Klingons genetically engineer themselves? If not, this is hard to square with such a (relatively!) hard-science show. In order for that to happen through evolutionary processes, you would have to have chance mutations give them double (or higher) hearts, and that would have to happen for all the organs, and the selection pressure for warriors that survive (otherwise) fatal blows would have to be happening all throughout that process.
Telomeres, which protect your DNA from unravelling, degrade with age. I don't keep up with the aging literature but I've heard this mentioned as one of the major reasons determining the human lifespan.
Regarding the "twice your organs" thing - think of all the concurrency issues they can now experience! A new failure model.
> If you consider the fact that human males who live to 80 have a 80% chance of prostate cancer (IRL not Star Trek), it seems like we live with time-bombs that do eventually go off.
Except prostate cancer comes in different forms, and many old men die with it, not of it.
Readit News
[1] http://biology.unm.edu/pwatson/Humphrey%20The%20Social%20Fun...
It's not exactly wrong, but it's way too anthropomorphic and attributes way too much intent.
Plus there's plenty of natural stuff which at least looks way over-engineered or redundant/unnecessary in its current form. The Mantis Shrimp's eyes for instance. The gallbladder also seems mostly redundant, and while one can argue that the lobed paired design of lungs is necessary considering the common occurrence of respiratory diseases redundant kidneys seem less than necessary.
As an aside, one really cool thing that happens in the case of a collapsed lung, is the trachea will shift toward the healthy side under less pressure. Called a tracheal deviation https://en.wikipedia.org/wiki/Tracheal_deviation
The gallbladder has a heap of design flaws but it is quite useful (until it causes problems). Bird lungs would be much more efficient a design as they don’t have dead space in the way ours do. And having 2 of an organ has more to do with our bilateral body symmetry which was an early evolutionary choice of our line than anything else
https://en.wikipedia.org/wiki/Recurrent_laryngeal_nerve#Evid...
Evolution does not care at all about fixing waste, unless that waste harms the individual's ability to procreate.
This made me start wondering something... at what point can something be attributed to intent? When did the first intent arise? If humans are blobs of matter following the laws of physics, why can we possess intent when nature cannot? What is the simplest process which can have intent?
This is probably just a restatement of an existing problem like where does intelligence come from. Just a random though I had reading your post.
http://johnhawks.net/weblog/topics/urban_legends/henry_fords...
A few sources that support this thesis are the books, "Nonzero: The Logic of Human Destiny", "The Elephant in the Brain", as well as this paper: https://deepblue.lib.umich.edu/bitstream/handle/2027.42/5717...
Nature makes a lot of pull requests, but has a great peer review system that prevents bad design entering the core of the system.
the author makes some absurd comments. "There doesn't seem to be any fundamental reason why an animal couldn't evolve which makes steel, for example. It would get its raw material like we do, from iron ore."
how does the author expect our bodies to produce heat in the thousands of degrees to burn out the impurities in iron and infuse carbon in its super heated state? i dont buy their argument that our bodies can make anything just because its building stuff at the molecular level. humans survived a lot of extinction level events, a lot of global famine. even if we could do the former, we might have gone extinct if we had extraordinary dietary requirements of iron. and what ever animal we evolved from would have also had to deal with that, and they experienced even larger extinction level events.
i was thinking about why the dinosaurs had such small brains. other animals and reptiles living today existed in the same period, and they had larger brains, so I thought the dinosaur brains were small by design, why?
i think because being big was adventitious, and being egg layers, only so much air can travel through a membrane. some eggs were as large as 2 feet long, probably not a lot of air getting into the whole system, so a hulking brain is a waste. even if they had small eggs, they needed the ability to evolve / or activate genes to grow big when allowed to do so.
The bone is a fascinating organ and sadly misunderstood by most people. They are, essentially, living rocks. Our bones are innervated, full of living cells, and constantly engaging in a chemical equilibrium with the body on CaPO4 as you point out.
Furthermore, the bone needs to grow along with the creature. It has to be soft enough to accommodate childbirth but allow growth and hardening as the organism matures. The process by which this occurs in natural bone is complex and remarkable.
Metal bones can't do any of this stuff.
Deleted Comment
They are! Calcium is a metal.
From that point of charity we can start to say things like "Organic environments cause corrosion in commonly-available pure metals", or "Pure metals can be toxic to animal cells in large amounts".
If it is possible to for the body to synthesize whatever material, it can create a frame for the bones, then wrap that frame in bio-active layers. Basically, a skeleton for the skeleton. Given the intricacies of other body organs (think the sizes and complexity of the eyes, says), such is not too hard of the task.
In fact, this probably answers all other concerns raised here. Corrosion and electric-conductive? A bio-compatible wrap (similar to enameled steel) solves that. Grinding between different bones? The ends of the bone can be built out of different material than the fragile length.
Furthermore, none of these concerns matter for, says, horns, especially the tips. Evolutionary speaking, it makes complete sense for animal to evolve steel-tipped horns: these steel parts hurt no one but their enemies.
(also note, carbon fiber avoids a lot of these bio compatibility issues).
In other words, animal kingdom did not have metal parts because synthesis is impossible, rather than because of disadvantages of metals per se.
Lightning might be an important consideration here. An animal's chances of getting zapped would go up significantly if they were waving around metallic horns in a storm.
Consider this: there must have been quite a lot of prehistoric humans who died, or otherwise suffered reproductive failure, because they lacked eyebrows.
Breaking major bones, especially in times before modern medicine, was without a doubt a life-threatening event. And considering the prevalence of fractures today, with our largely sedentary lives, it must have happened fairly often
Holding our bodies erect is a pretty important job too.
His major answers are that electrical conductivity is likely to be a huge problem for the nervous system, and that iron and aluminum readily oxidize (aka rust). Iron oxidization is useful in hemoglobin but would be problematic in your bones, and while a body could be designed with conductivity in mind, it would at minimum also take a reworking the nervous system.
1: https://biology.stackexchange.com/q/9419/4101
> Firstly, fully reduced (oxidation state 0) metal has a high energetic cost to create in reduced form.
Basically, it takes a ton of energy to make steel. We are literally burning gigagallons of over a billions years worth of pressurized organic matter to have made all of the steel we have made in the past century and a half or so. We could make a super inaccurate but somewhat plausible estimation that we have used something like 150 million years worth of the entire earth's lifeforms at the time's dead bodies and converted that into 150 years worth of steel. So if my orders of magnitude are correct...it would be something like a million times more difficult energy-wise for an organisms to create steel from scratch than calcium-based hardened material.
That's assuming we have burned through 15% of a billion years worth of oil from bacteria, that 100% of the bacteria converted into oil and then converted directly into steel, and that there was only a billion years of bacteria to oil creation. I am sure these numbers are off, but maybe that means it's only 100,000 times or 10 million times more difficult for organisms to make steel rather than bones.
— Is nontoxic. — Is biocompatible, and can semi-integrate into bones, a process called osseointegration[1], which makes for much better implants. — Isn't ferromagnetic, so you can use MRI to examine and maintain implants safely. — Is less conductive than many other metals.
1: https://en.wikipedia.org/wiki/Osseointegration
Also, related : https://biology.stackexchange.com/questions/60780/how-to-for...
More importantly, neurons use ion gradients across their membranes to conduct signals. It's not electrons flowing along, as it is for wires.
While the magnetic field created by thousands of neurons firing in concert can be picked up using wires (EEG, ECG), and neurons can be induced to fire with electric shocks, I actually doubt anything would happen if you were to connect two neurons by wire.
At the very least, the wires would need to have contact with the axons (neuron terminals). A neuron can be a meter long, but it is isolated by a fatty membrane along its body.
> The activation energies for oxidation and reduction of iron are of the order of 30-60KJ/mole, comparable to the figure of 57KJ/mole for ATP, a molecule which is commonly used for delivering energy around our bodies. We normally make iron from its ore at very high temperatures, because the rate-limiting process is diffusion in the solid state. But the body makes materials in a very different way, from the bottom up, atom by atom, molecule by molecule. And of course the fact is that you are already oxidizing and reducing iron inside your body all the time.
It's worth remembering that Calcium (the substance bones are made of) is, in fact, a metal [1]. And our bodies have no problem growing and repairing our bones. Why wouldn't that happen with steel?
Also- the bit about the stresses that a titanium alloy bone would experience in its lifetime- yeah, that, probably. We probably have bones as tough as they need to be, or _needed_ to be in the last million or so years.
________________
[1] A factoid that my 16 year-old self, obsessed with Metal (the music) found deeply satisfying. "Dude, my bones are made of METAL".
Well, yeah. I think evolution makes you as good as you need to be to reproduce before you die, rather than optimise every characteristic.
The Earth's crust is 3.6% calcium, and we get more than enough of that in our diet...it's 5% iron. There's even a lot of titanium - fully 0.6%, much higher than 'rare' elements like carbon! [0]
I don't think we'd have any trouble getting it if the metabolic and biological systems that are employed to get us calcium were instead employed to produce titanium.
[0]: https://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth...
Because that's what's good enough to get through the crucible of successful genome transmission? Evolution doesn't have an end goal; every "improvement" came about by random changes, either in the genome or in the environment, which yielded a reproductive advantage to some new gene or genes. I'm not sure if the author intended it but this seems to fall into the common fallacy of believing that evolution is an active process guiding organism toward some optimal state. Organisms don't evolve "to do" anything. They end up there. Contemporary genomes are what's left after everything else has died. Not the conquerors of mountains.
[1] http://www.seafriends.org.nz/oceano/seawater.htm
Deleted Comment
Then all of this stuff is adding more weight, we're going to need bigger or more powerful muscles to move it around well. Then we'll need bigger/better heart, lungs, circulatory system to fuel that extra muscle power, and improved digestive system to get more energy for that stuff into the body. Skin is seeming kinda fragile with all of this extra bone strength and muscle power, better toughen that up too.
So why aren't our bones made out of polyimide-polyamide-fiberglass composite?
Not that evolution is able to actively design things in that way, of course. More like it was an evolutionary advantage for those ribs to be flexible, but any flexibility in arm and leg bones and other major bones was not an advantage.
For example: during a famine, perhaps a growing child with "normal" bones is much more likely to survive than a steel-boned counterpart who is unable to find the required extra iron ore and energy needed to grow.
If you consider the fact that human males who live to 80 have a 80% chance of prostate cancer (IRL not Star Trek), it seems like we live with time-bombs that do eventually go off.
Regarding the "twice your organs" thing - think of all the concurrency issues they can now experience! A new failure model.
Except prostate cancer comes in different forms, and many old men die with it, not of it.