Why are bones not made of steel? (2010)
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[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...
Ummm, fair enough. But then you say...
> My genes want to beat your genes
Your genes don't want anything. They have no desires. No emotions. They're just molecules. Long, complex polymers, granted, but just molecules, nonetheless.
Humans are still evolving. Probably faster than ever. See http://www.pnas.org/content/104/52/20753.long .
What does "a long long time ago" mean to you?
It's only 65M years since mammals underwent the massive adaptive radiation after the K–T extinction.
It's only 50,000 years since the human population started to greatly increase. (See previous reference.)
You need to be very careful in looking for references which support your thesis. You'll not find good counterarguments that way.
Be very cautious about any reference which emphasizes "dominance hierarchy" in humans, especially when based looking towards chimpanzees (Pan troglodytes) as a model for understanding how early humans interacted.
Only more recently have we been looking at bonobos (Pan paniscus), which are evolutionarily equally distant from us. The thing is, bonobos have rather different behaviors than chimpanzees, including in how they deal with dominance.
Unfortunately, a lot of wide-spread cultural beliefs on this topic are wrong, or at least much more controversial than can be used as the basis for any good understanding. See for example "alpha male" at https://en.wikipedia.org/wiki/Alpha_(ethology)#Controversy and https://www.youtube.com/watch?v=0Ti86veZBjU .
I would advise you to look for books by people who work in, or very closely to, anthropology, archeology, and genetics. And stay away from evolutionary psychologists, most of whom in my experience have a flawed understanding of evolution.
As an example of a warning flag, your last link, a book from 1990 is pre-genome, and talks much more about chimps than bonobos.
You might be interested in "Why are there so many explanations for primate brain evolution?" at http://rstb.royalsocietypublishing.org/content/372/1727/2016... .
They argue that the Social Brain Hypothesis (SBH) has the strongest support:
> SBH is an explicitly two-step process: an ecological problem is solved socially (i.e. as a cooperative process) and a big brain is needed to allow the requisite level of sociality to do this. The group created by big brains is not an end in itself (a mistake made by many attempts to compare between alternative hypotheses: e.g. [18,103]), but rather the means to an ecological end. It is important not to mistake this view for group selection: it does not involve the differential survival or extinction of groups. Rather, it is a group-level or group-augmentation explanation (sensu [104]), such that individuals living in larger social units have higher fitness than those living in smaller ones.
The only mention of "dominance" in that publication is in the title of a citation to a paper from 1980.
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.
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".
Nothing like dropping the clutch on your new 800 hp motor and having the rear axles snap. Or have the flywheel disintegrate and saw through the bell housing and your feet.
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
A bit pedantic, but: there doesn't need to be a direct line between a morphological feature, like eyebrows, and death and/or inability to reproduce. Evolution is a statistical process that operates over an entire population of organisms. So, a feature like eyebrows can evolve even if they have a relatively minor impact on organisms with eyebrows, like, say, by making them 3% better at hunting or whatever. Because if you have a population of thousands or millions of organisms, that 3% hunting advantage will make a difference.
1. Eyebrows are a pretty elaborate structure to have evolved purely by chance.
You don't get from not having eyebrows to having eyebrows via a single mutation. It seems reasonably likely that the specific shape of eyebrows (as in, one person has bushy eyebrows and another has thinner eyebrows) might be tied to sexual selection (as in, the variations don't serve a functional purpose other than being attractive to the opposite sex). But that eyebrows exist at all is probably tied to some survival/reproductive benefit.
2. I think you underestimate the impact that something as a small as, say, a 3% improvement in an outcome can have on the evolution of a specific trait.
You can use a spreadsheet to model this yourself. Start with a population where 1% of people possess some trait that allows that subpopulation to have 3% more children per generation that the other 99% of the population. I'm showing that it takes a little over 150 generations for the descendants of that first group to comprise 50% of the population. As a point of comparison, there have been roughly 7,000 generations of humans. So, you can see that natural selection will act even on minute details of anatomy because when you play them out for many generations they matter.
We will probably never have a definitive answer to the question of why we have eyebrows. The best we'll ever do is some decent hypotheses. So if the argument is that eyebrows serve function X, but we find out in the future that eyebrows do not, in fact, serve function X, then a naive observer will think that eyebrows did not evolve to serve any purpose and are, in fact, just a random feature.
IMO, a more thorough argument is to point out that the only way species-wide, complex morphological features like eyebrows can possibly exist is if they serve an important purpose, even if that purpose has a miniscule impact on the outcomes of any given organism. This argument is resistant to any given explanation for the purpose of eyebrows turning out to be wrong.
Plus it gets to a deeper understanding of evolution.
P.S. I'm skeptical about the sweat in the eyes explanation for eyebrows. Anecdotally, my eyebrows have never kept sweat from getting in my eyes. And less anecdotally, if you spend a few minutes looking at somebody's face and imaging sweat rolling down their forehead, you'll see immediately that eyebrows aren't very effective for sweat diversion.
My money is on protecting our eyes, which are our most important sense organs. If you google image search "mma black eye", you'll see what I think is kind of remarkable: despite serious trauma to the surrounding areas, most people's eyes are intact.
That's not an argument. It's a tautology. In any field other than evolution, such a statement would be ridiculed.
There are infinite reasons that could explain eyebrows. Design. Alien intervention. Lamarckisn processes. The Will of the Flying Spayhetti Monster. Out of this myriad of possibilities, if you suggest they arose because and persisted due to conferring a survival/reproductive benefit, the burden is on you to demonstrate such. This can be done in two ways. The first is by storytelling... creating a Kipling-esque 'just so' story involving, perhaps, sweat or sexual attraction or whatever. The second method is by using science. Namely, measuring the degree (if any) that eyebrows effect survival/reproduction. From that number, one can backtrack and determine mathemstically how many generations it would have likely taken for the phenotype to become ubiquitous, and see if it lines up with other assumptions. To summarize, before conjuring up 'just-so' stories, find 1,000 people with no eyebrows, a 1,000 with bushy eyebrows, and show me a measurable difference in their fecundity rates. Or, use chimps. Or, dogs. Doesn't matter. As mentioned, I personally don't think eyebrows have squat to do with survival/reproduction... you can't counter my null-hypothesis by assuming a priori that every phenotype must confer some sort of advantage.
I tend to agree with you that a lot of things that are called "science" are mainly story telling. There is "physics envy" for a reason. Physics focuses on a very small subset of reality that have observations that are true with uncertainties of 5, 6, 9 sigmas. This is the level of truth one needs to build up a models of complex things that match reality almost all the time. Physicists at LIGO or CERN don't publish in journals some observation with P=0.05 and expect others to use it. Hopefully the reproducibility crisis in psychology will get many truth seeking fields to spend more time on understanding what is true at the lowest level. Feynman had a good essay about this issue many years ago about rat studies[1,2].
[1]Feynman's Caltech speech:http://calteches.library.caltech.edu/51/2/CargoCult.htm [2]More recent short essay on the rat study: https://www.realclearscience.com/blog/2014/02/the_rat_experi...
I guess I consider the eye brow just the hair on the surface and maybe the skin/muscles to move it, not the whole bone structure underlying it.
You wrote: But that eyebrows exist at all is probably tied to some survival/reproductive benefit.
I disagree. Not every trait has something to do with conferring a benefit. Many traits are simply random artifacts of an exceedingly complex dynamic system. Your assertion hypothesizes otherwise. That's fine. But, it would be reasonable to expect data to back it up. In my experience, I've seen no correlation between eyebrows and the number of offspring.
As far as your second point, 3% is enormous. But, in any case, the problem is a failure to appreciate that there is a 'noise' threshold below which a probabilistic benefit will have no effect. That is, the length of my pinky may have some miniscule effect on the number of my offspring. But, if the effect is too low, it simply will not have an effect no matter how many millions of generations go by; the randomness of life will swamp it out. To put it in information theory terms, the signal would be indistinguishable from the noise.
Many people pay money to disagree with that assessment, at least according to sales of eyebrow pluckers, waxers, and makeup kits that are specifically designed to make it more attractive.
Either those people are wasting their time (which needs explanation, since over time people who waste their time and money on things that don't aid reproductive success should be selected away). If it does matters to their reproductive success, then it reflects either cultural or a deeper preference.
Personally, I have heard people comment about people who either lack eyebrows (usually through some stupid prank or accident) or have very thick eyebrows.
Not having eyebrows definitely interferes with facial signaling, and we signal quite a bit through eye contact. 'The eyes are the windows to the soul'. The eyebrows frame them.
We've arrived at a circle in this thread, considering the eyebrow example was initially offered to show how even small advantages will, over time, make some phenotype (and genotype) dominant.
This is also mathematically true: given a coin with only the most minimal bias, cumulative results of coin tosses will eventually drift far away from 50%/50%.
Concerning your empirical observation regarding the evolutionary usefulness of eyebrows: How many people have you seen being clearly impacted (in regards to their offspring) by missing toes, being born with only one kidney, having ears shaped sub-optimally for capturing sound etc...?
Because extremely little regarding your body is left to chance. Unless you're one of less than a hundred with a given feature, be assured that it's a variation that, for a significant number of prior generations, has proven to be useful.
This is what troubles me. I understand your point. But, if it takes a trillion years to 'drift away from 50/50' is it meaningful to describe the bias as something other than zero? That is, is there some Plank's Constant kinda-thing for probabilities? The reason this always comes to mind is the absurdly low probabilistic effect on fecundity of, say, a finch having a 4cm beak versus a 4.1cm beak. If the effect is some probability so low that it would take millions of generations to manifest itself, then, in light of the fact that finches were probably single-celled organisms a million generations back, the probability may as well be zero.
In that spirit, here's the next volley:
> I disagree. Not every trait has something to do with conferring a benefit. Many traits are simply random artifacts of an exceedingly complex dynamic system.
As I said previously, given how complicated of a feature eyebrows are (they have a skeletal component, hair, and muscles which contribute in complex ways to facial expressions), there is no plausible way the existence of eyebrows is due to random variation. Eyebrows would require a whole bunch of very specific mutations to occur at once and mutations are rare. The specific form that people's eyebrows take probably has a fair degree of randomness, but that eyebrows exist at all cannot be due to chance.
Further, every single person has eyebrows. If whether or not a person had eyebrows were truly of no consequence to genetic fitness, some people would have them and other wouldn't.
> But, it would be reasonable to expect data to back it up.
This argument goes both ways. As you say, I have no numbers to show that eyebrows are under selection, but you have no numbers showing that they are not. But your position is worse than that, since you are lacking a plausible explanation for how eyebrows can even exist, given how complicated they are anatomically, without having been selected for.
> In my experience, I've seen no correlation between eyebrows and the number of offspring.
That's not entirely true. After all, only people with eyebrows have children. :P I am only party kidding about that, btw. Per my previous point, the fact that everyone has eyebrows means that they contributed somehow to people having children.
But more seriously: surely you can agree that eyebrows have an impact on attractiveness. After all, a great many people, both male and female, pluck, shape, thin, or color their eyebrows. And surely you can agree that attractiveness at one point was linked to reproductive success (though I agree that it probably has a limited correlation in modern life)?
> As far as your second point, 3% is enormous. But, in any case, the problem is a failure to appreciate that there is a 'noise' threshold below which a probabilistic benefit will have no effect. That is, the length of my pinky may have some miniscule effect on the number of my offspring. But, if the effect is too low, it simply will not have an effect no matter how many millions of generations go by; the randomness of life will swamp it out. To put it in information theory terms, the signal would be indistinguishable from the noise.
If you make the change in outcome 0.3%, I'm showing that it takes 1,500 generations for for the offspring of the starting 1% subpopulation to reach 50% of the total population. That is all things being equal, etc., etc., but still not very long in evolutionary terms. The thing about evolution is that it acts on gene frequencies in populations. That allows the effectiveness of very minor changes in genetic fitness to be assayed over time. And the larger the population, the more precise the assay is.
But it also means it might not have appeared for a specific reason in humans. It might very well have just been there and useless (but not detrimental) at one point, then used for something.
They're not that prevalent, and they may not have been more prevalent in the past, sedentary life likely contributes to some form of osteoporosis by providing less continuous stress and it adds "extreme" sports as discrete high-risk events.
And of course just because it's life threatening does not mean it's going to be weeded out, selection is an important part of evolution.
The thing that brought this into full relief for me was the story of Brian Jones, a member of the Starting Strength community. He fell off of a roof and shattered both legs. Doctor told him he would never walk again, etc., etc. But he did. And then he start lifting weights. Of course, his body adapted to the increasing load he was placing on it.
Specifically, his body responded by growing muscle and making his bones more dense. His bones got so dense that the metal pins which were inserted into his leg bones after his accident started getting pushed out into the surrounding flesh and he had to have surgery to remove them (links to his story below).
I would bet good money that the majority of bone breaks (excluding things like car crashes and obvious stupidity), even in children, are a result of our largely sedentary lifestyles interacting with our body's evolved tendency to not engage in metabolically expensive activity like growing muscle and denser bone unless it receives signals indicating that they are actually demanded by our environment.
Brian Jones' story:
Video form: https://startingstrength.com/resources/forum/articles-and-pl...
Written form: https://startingstrength.com/article/barbell_training_as_reh...
About sedentary lives, I'm fairly convinced that nomadism made for stronger everything, bones, tendons, muscles (coordination too) so their lifestyle (granted you're not living near cliffs and have enough food) didn't increase the % of fracture.
Of course human minds would tend to underestimate this. Evolution harnesses the parallelism inherent in reality and atoms. Natural selection operates at all levels of detail at once.
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.
> 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.
("In Creationism, special creation is a theological doctrine which states that the universe and all life in it originated in its present form by unconditional fiat or divine decree." - https://en.wikipedia.org/wiki/Special_creation )
Take this quote from "The Vanishing Case for Evolution" by Henry Morris, http://www.icr.org/article/vanishing-case-for-evolution/ one of the founders of the Institute for Creation Research:
> The absence of evidence for evolution does not, by itself, prove creation, of course; nevertheless, special creation is clearly the only alternative to evolution.
How can special creation - one type of creationism - be both a "metaphor for evolution" and "the only alternative to evolution"?
Obviously it can't, which is why it's incorrect to summarize creationism as you did.
Progressive creationism is more accepting of evolution, in that it says "microevolution" occurs but "macroevolution" does not. Even this cannot be seen as a metaphor for evolution, because it rejects part of evolution.
Perhaps theistic evolution fits your description (https://en.wikipedia.org/wiki/Theistic_evolution ) but otherwise most types of creationism do not.
— 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.
Also, related : https://biology.stackexchange.com/questions/60780/how-to-for...
"So it seems that there are no fundamental reasons why animals could not evolve a metal skeleton"
The main reason is that most multicellular organisms (especially vertebrates) go through developmental stages where they grow in size. Mineral bones can be grown like this, while metal ones probably could not.
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.
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[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...
Almost all our carbon goes back to the air.
This leads to the interesting concept that when you are losing weight, you are actually exhaling most of your weight loss.
Edited: Downcommenter is correct. Sorry, glitched. I was thinking about various things and pulled plants into the mix when the article is only about humans.
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.
Still, it relies on harnessing our spatial reasoning and I don't think most people are good at visualizing or reasoning about billions of marbles being sifted through billions of nets (in the case of simpler organisms) or even millions of marbles being sifted through ~7,000 nets (in the specific case of humans).
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.
Most of it is to remove genetic birth defects, but there was an entire arc in Enterprise about how a large population of Klingons were genetically altered to give them superior strength and skills. So it's possible that it was related to this, or was engineered at some point in a similar fashion. The whole arc was only to explain why the Klingons looked different in the early series and movies. Berman and Braga tried their best to keep the canon intact, and to have it make sense.
Well, all humanoid races (as revealed in TNG) in the galaxy (or maybe only in the Alpha and Beta quadrants) were genetically engineered by and from a common precursor race visiting from elsewhere, so if you take “themselves” broadly enough, yes.
They also kind of disastrously tried to genetically engineer themselves much later, borrowing from humans doing the same thing, but that's not the source of their unique anatomy (though there's no reason that has to be the only time they did that.)
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.
1. We evilved from the sea, where Calcium is far more abundant than metals 2. Having a skeleton 100x harder than out current one, would require 100x stronger muscles and tendons, if you don't want them to snap 3. You couldn't swim with metal bones, which would again be a problem with 1., and make it hard to survive as a species if you drown very easily.
Other arguments, which however, were debunked
1. It takes too much energy to create steel. It doesn't, maybe twice as much. 2. You also have other bone functions. However, you could also have those with a semi-steel, semi-organic bone structure. 3. Bones need to decompose, so that you don't steal too much resources from the environment. Possible argument?
Regular structural steel, used for all sorts of typical building applications, has a yield strength of 250MPa and an ultimate tensile strength of about 400MPa. So bone with it's 150MPa tensile strength, about 60% that of steel's yield strength, is pretty good!
For comparison, typical structural timbers have a tensile strength of around 18MPa.
The proper way of conducting this kind of material comparison would be finding the design limit. In this case it would be probably either toughness/weight of fracture toughness/weight. Then if you are unable to come up with specific grade of metal that simply beats bone, you have absolutely no case. Typically alloying for high strength decreases both toughness and fracture toughness.
If you had titanium bones, you wouldn't become hunch-backed and short in old age, nor would your fingers deform.
A better question would be: why haven't organisms evolved which use iron in their skeletons?
Having a transparent blood could have pros and cons, like hiding the level of injuries to the other antagonist in a fight, but you need copper for that.
On the other hand, if you could replace a bone by a hollowed tube of metal, you could bassically smuggle anything that you want at plain sight. Even radioactive substances. Such procedure would be quickly forbidden.
Also, the 'explanation' begs the question, why wouldn't we see a bone replacement evolve that's suited for iron reinforcement? Your clarificiation is a small step down the 'whys', but saying "because bones have evolved to use calcium" is tautological.
Or put it another way, the difference in density between seawater and fresh water is about 3%, and it's noticeably easier to swim in the sea. So if you have bone replacements that make you 3% heavier, you should expect to notice it.
On the other hand, the article compares bone to metals on an equal-weight basis.
[1] http://www.huronscuba.com/equipment/scubaCylinderSpecificati...
This really messed with my head when I swam in Lake Constance last year. I was so used to swimming in salt water than the different buoyancy in fresh water completely threw me off for a couple of minutes.
I also have the opinion that bones enable healthier predator/prey relationships because they're just weak enough to get pulverized by a larger physical force (i.e. from a predator). I realize teeth could be steel as well, but in that case muscle would no longer be enough to completely crush a skeleton.
Nature really seems to value materials that are just strong enough to get the job done, but just weak enough to get reclaimed easily.
http://www.bbc.com/earth/story/20151014-superpowers-of-the-n...
http://www.newsweek.com/orcas-killing-great-white-sharks-eat...
(See also the carboniferous period, before the evolution of wood-decomposing bacteria. 60 million years with no decomposition!)
The carboniferous period sequestered a huge amount of carbon. That's a process spread across an enormous time frame. But, that was primarily atmospheric carbon, which can be circulated much better than terrestrial minerals. Since it was atmospheric, you wouldn't have localized shortages (air currents bring in fresh air). It took much longer, but the trees of the period gradually choked themselves out by pulling too much carbon out of the air. It just had to happen on a planetary scale and geologic time frame.
I would also say that nature does make metals, it just needs to go through a behavioral layer.