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Why are bones not made of steel? (2010)
- westmeal 9y agoIt's a cool idea and forgive me if I'm wrong but don't the bones in the body create new T & blood cells using the bone marrow? If every bone was replaced in your body how would you generate new cells?
- verelo 9y agoAlso, weight! Bones are not weightless but steel...
- pmlnr 9y agoSteel/metal foam is surprisingly light, a bone-fabric like structure of metal would be pretty light as well.
- jablan 9y agoAlso, steel pipes, as on bicycles.
- yoz-y 9y agoWhat about joints? Wouldn't harder bones wear them more quickly?
- anotheryou 9y agothis was my main thought, but maybe foamy constructions can stay springy
- BjoernKW 9y agoEasy: Exchange the blood for something entirely different, too ...
- westmeal 9y agoTrust me I'd replace blood with transmission fluid any day but that's pretty far from an organic being eh
- jacobush 9y agoI guess you could create a hollowed out titanium bone and keep the yummy bone inside. Probably even a titanium/bone composite where most of the strength comes from titanium but where enough bone and bonemarrow was still there to make if function as a regular bone.
- Amorymeltzer 9y agoSurprised 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. 1: https://biology.stackexchange.com/q/9419/4101 https://biology.stackexchange.com/q/9419/4101
- jstanley 9y agoIf conductive bones are problematic, why do Titanium pins etc. not cause problems?
- Amorymeltzer 9y agoFor 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. 1: https://en.wikipedia.org/wiki/Osseointegration https://en.wikipedia.org/wiki/Osseointegration
- epmaybe 9y agoAs an aside, there was a professor of mine in college that had a startup to apply an electric current through some rods and pins to stimulate osteoblast formation and therefore better osseointegration.
- gilleain 9y agoAnother 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. Also, related : https://biology.stackexchange.com/questions/60780/how-to-form-biological-metallic-tissue https://biology.stackexchange.com/questions/60780/how-to-for...
- YeGoblynQueenne 9y ago>> 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".
- yoz-y 9y agoI 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.
- lawlessone 9y agoafaik Aluminium also requires an electric current is run through it while being refined. It's more than complicated metals like iron.
- yorwba 9y agoThe 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.
- yoz-y 9y agoHow much heavier could one's bones get before they would not be able to swim anymore?
- deleted 9y ago[deleted]
- mnw21cam 9y agoTo answer that question, have you ever tried to swim with a 1kg weight belt? Such devices are commonly used by scuba divers to maintain neutral buoyancy. 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.
- KozmoNau7 9y ago> the difference in density between seawater and fresh water is about 3%, and it's noticeably easier to swim in the sea 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.
- gaius 9y agoI add 2kg when diving in saltwater, but it will be different for everyone
- mannykannot 9y agoAt least part of the ballast normally carried by divers is to compensate for the buoyancy of either a wet- or dry-suit, and for the buoyancy of SCUBA tanks (some are buoyant when empty, at least in seawater [1].) Treading water while carrying an extra kilogram would be quite a struggle for many people. On the other hand, the article compares bone to metals on an equal-weight basis. [1] http://www.huronscuba.com/equipment/scubaCylinderSpecification.html http://www.huronscuba.com/equipment/scubaCylinderSpecificati...
- smileysteve 9y ago
- kazinator 9y agoBone in fact sucks at repairing itself in the face of age-related degeneration such as osteoporosis, arthritis and such. If you had titanium bones, you wouldn't become hunch-backed and short in old age, nor would your fingers deform.
- ceejayoz 9y agoI don't see how titanium bones would remove the need for healthy cartilage, and I'd expect if we had metabolic pathways to create titanium we'd have ones to break it down, too.
- toasterlovin 9y agoI would not discount the effect that sedentary lifestyles may have on degenerative diseases. Modern life is a huge confounding variable when evaluating the effectiveness of our bodies.
- kazinator 9y agoModern life means having an unprecedented probability of living past forty.
- CapitalistCartr 9y agoBones can give and break. This can be a benefit. Better to break a bone than rend the flesh in many cases.
- taneq 9y agoMore importantly, better to break a bone, then let it knit back together more-or-less as it was, than to bend a bone and be stuck with a permanently bent limb.
- FreeFull 9y agoOn the other hand, if a fully broken bone isn't set properly, then you are stuck with a permanently bent limb anyway.
- hotsauceror 9y ago"...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.
- toasterlovin 9y agoEvolution 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.
- hotsauceror 9y agoIt 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.
- toasterlovin 9y agoFWIW, I don't think the analogy you described is what many people would describe as "fairly intuitive", though I think it's a reasonable one. 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).
- falsedan 9y agoFor starters: the body would oxidise them & they would rust, and the detached flakes would travel to other parts of the body, blocking blood vessels or causing iron poisoning. A better question would be: why haven't organisms evolved which use iron in their skeletons?
- JoeAltmaier 9y agoMarrow is full of it !
- falsedan 9y agoinsects ain't got none, son
- comicjk 9y agoBone is a composite material, made of calcium phosphate interwoven with collagen fibers. It's not clear to me that structural bits of iron would integrate well into this structure.
- pvaldes 9y agoBlood cells contain iron. This is the reason to blood being red instead the cyan or transparent blood found in hundred of extant animals. 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.
- falsedan 9y agoIt's not clear to me what your point is. Are you saying that my suggestion that the article should have addressed a different (similar) hypothetical is at odds with your imagination and the physical structure of bone?
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- rlpb 9y agoEvolution 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.
- Pigo 9y agoI 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.
- hotsauceror 9y agoTelomeres, 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.
- SilasX 9y agoDid 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.
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- nmeofthestate 9y agoI'm not so interested in what bones are made of - I've never broken one. However, I'd love it if my joints could be replaced with something less awful.
- buckthundaz 9y agohttps://www.youtube.com/watch?v=LGUhVelktk4 https://www.youtube.com/watch?v=LGUhVelktk4 http://www.toddbumgardner.com/hip-and-shoulder-mobility-the-cars-solution/ http://www.toddbumgardner.com/hip-and-shoulder-mobility-the-...
- Gatsky 9y agoBone 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.
- agumonkey 9y agoGood 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.
- matt4077 9y agoIt'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
- masklinn 9y ago> 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 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.
- danso 9y agoFun read. I was thinking the answer would simply be kind of the same as the reasons for not making an entire plane out of whatever its "indestructible" black box is made of.
- ufmace 9y agoAlso 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.
- logfromblammo 9y agoI 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?
- ufmace 9y agoI 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.
- jdonaldson 9y agoBones not only have to be structurally sound, they also have to be decomposable. Otherwise skeletons would never go away, and it would be too difficult to reclaim the raw materials from them. 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.
- BurritoAlPastor 9y agoWhy do bones need to decompose? What possible evolutionary pressures could be exerted for traits that aren't expressed until after death? (See also the carboniferous period, before the evolution of wood-decomposing bacteria. 60 million years with no decomposition!)
- jdonaldson 9y agoDon't confuse trait selection for evolutionary pressures. If previous generation exhaust or over-sequester resources it dooms the species that relies on them. 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.
- mannykannot 9y agoEven if the current situation is a global optimum in the sense you propose, it would be purely coincidental, as evolution doesn't do global optimization or long-term planning, and prey does not adapt for the convenience of its predators.
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- tw1010 9y agoFrom "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" [1] http://biology.unm.edu/pwatson/Humphrey%20The%20Social%20Function%20of%20Intellect.pdf http://biology.unm.edu/pwatson/Humphrey%20The%20Social%20Fun...
- masklinn 9y ago> 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.
- kmano8 9y agoI'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 https://en.wikipedia.org/wiki/Tracheal_deviation
- grondilu 9y agoAren't all biological tissues made out of proteins? I mean, the very mechanism of DNA transcription implies that products are necessarily polymer-like, if I understand correctly. DNA can't make metals. I suppose some purely enzymatic mechanism could produce 3D-cristals (a metal is a macroscopic aggregate of microscopic crystals, right?), but apparently no such mechanism exists. It'd be great though, as we could probably replicate it. I would also say that nature does make metals, it just needs to go through a behavioral layer.
- lurquer 9y agoIncorporating steel into bones (and, presumably shells) would result in lifeforms that would be very difficult to kill. It may be the case that an ecosystem cannot establish itself if the members' defense mechanisms are too strong. It may be physically impossible to evolve muscles strong enough to crush a steel skull. (Or, at earlier stages, to crush a clam.) Is there not an evolutionary pressure that tempers the establishment of defense mechanisms (such as steel-plate covered creatures) that are too effective?
- theophrastus 9y agoThen 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. [1] http://www.seafriends.org.nz/oceano/seawater.htm http://www.seafriends.org.nz/oceano/seawater.htm
- deleted 9y ago[deleted]
- Houshalter 9y agoEvolution is all about local optimas. If you can't reach your goal with just a series of small improvements, it can't happen. The article claims an organism could just eat metal ores. Sure, but to do that you need to start with an organism that already eats and digests ores. Presumably calcium bones evolved in an organism that already had a lot of calcium in it's diet for other reasons.
- deleted 9y ago[deleted]
- wellboy 9y agoSo, to summarize, we don't have a steel skeleton because 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?
- vlehto 9y agoI'm not an expert in the field, but I'm pretty certain the writer of this piece is neither. He is not using correct units and seems to be misusing the term "fatigue strength". 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.
- TheSpiceIsLife 9y ago> So let's look at the facts. The bones in your body are made from material which has a tensile strength of 150MPa, a strain to failure of 2% and a fracture toughness of 4MPa(m)½. For a structural material that's not good. We can make alloy steels that are ten times better in all three of those properties. 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.
- mattdeboard 9y agoYo this guy just explained the rock eater in Neverending Story