# Could human bone act as effective natural armor?

I've recently come across a disease that I am unhealthily intrigued by: Fibrodysplasia ossificans progressiva. Basically, instead of soft tissue healing normally, it calcifies and grows bone to replace damaged cells. This is, obviously, very unhealthy and currently lacks any form of treatment.

Now, onto the question. Would human bone be useful as a kind of armor/exo-skeleton? Could it prove light enough, but strong enough to protect against predators and the elements?

What I imagine is large flat plates that cover inflexible parts of the body (forearm, torso, etc) like a suit of armor might. Another possibility is that it grows as scales, which is more flexible.

For this question, I will assume that the armor grows with the body, avoiding the obvious health risks

EDIT: I just want to clear this up. I only reference the disease as the inspiration for the question. I didn't mean for it to factor into the question

• Based on the nature of the genetic condition, such ossification is rigid and inflexible. Thus, the victim would be incapable of bending by the bone growing around this body, to say nothing of the internal fusion of joints. But I'm assuming you're not dealing with the disorder itself, but rather a modification of it. – Isaac Kotlicky May 29 '17 at 13:55
• As a aside, thank you for inventivizing me to research the process of bone construction and molecular dynamics. This will take a while to write, though... – Isaac Kotlicky May 29 '17 at 14:19
• Very much related, though I don't think it is a duplicate: Could a creature evolve a biological “bulletproof vest”? – a CVn May 29 '17 at 14:43
• Check out various animals like turtles or armadillos. There are several examples in nature of something similar happening – Raditz_35 May 29 '17 at 14:48
• Erm, does it not already... after all armour protects... organs? Rib cage protects... organs?. Skull protects brain, etc. Obviously I think yes, it could do so. – djsmiley2k May 29 '17 at 16:31

It depends what you want to defend against but large plates might be good against claws - which are designed to cut through flesh - but there are some aninmals with the jaw strength to break bones.

But yes, bone is harder than flesh and would offer more resistance, therefore it is a form of armour.

Thicker bones give more protection but also add more weight. If we aren't changing the human too much (ie having a, literal, exoskeleton and no internal skeleton) we can look at how much weight is being added.

I found something that quotes human bone density as $1600$kgm$^{-3}$. Another source says the surface area of a human is $1.5-2.0$m$^2$. So, for a thickness of $1$cm of bone (can make this thicker or thinner if you like, this is just a ball park).

We get: $$1600 \times 2 \times 0.01 = 24 kg$$

This is quite a large proportion given average human body weight is around 80kg (I couldn't put that link in but a quick google shows it). You can tweak those numbers if you like. Maybe you only have plates on 1 square meter but you're still left with 12kg extra mass.

Humans are designed for running long distances, running away from predators or, as a pack, towards prey. The extra mass would seriously inhibit this and mean your new humans need to become bulky fighters rather than runners.

Some edits:

Firstly a few people pointed out that, in the army and such, modern humans can train to run with heavy armour (see Hankrecord's comments). I completely agree we can manage, however with the OP asking about predators I had (perhaps incorrectly) assumed this meant they were living in a hunter/gatherer type society where any and every edge you could get was essential. It seems to me humans evolved to run long distances and, assuming this was for survival, the extra carry mass of the bone would render this survival tool less efficient. This is why I proposed they would become bulkier fighters compared to their unarmoured counter-parts.

Secondly dlatikay provided this source which provides figures for the density of different bone types. They said:

So the weight could range from ~23kg (solid-massive) to ~6kg (spongy).

Which provides us with different uses for the bone - perhaps even different types (or classes) of armoured humans. Ranging from those with thick solid armour who might risk a run in with a heavy clawed animal to the lighter, spongy armoured humans who may be more useful as scouts, mountain climbers who may be better equipped to take a fall or some other attack where the force is spread out (rather than in a sharp tooth or claw).

• 1) Why do you think 1cm is enough armor? _______________ 2) this weight is not too much of a hindrance. Assuming the armored humans grow with their armor, they get used to that. – Mindwin May 29 '17 at 15:13
• Nothing said we were re-evolving the species, but good call on the weight issue. Is that for bone in general or compact bone in particular? I imagine the cancellous bone would be quite light but ineffective as armor. – Isaac Kotlicky May 29 '17 at 15:30
• @Mindwin I don't think 1cm will hold up to a lot but it was a lighter option I thought I'd start with to make a point about weight. The humans who grow with their armour will become more muscular - hence the final sentence about bulky fighters rather than runners. The bone increases the carried mass of a runner (mass that doesn't contribute to movement) so they will never be able to run as fast as a human without. I'm not saying they can't run, only their tactics would have to change - a slight difference in speed means you can't catch prey. – Ludo May 29 '17 at 15:36
• @dlatikay The OP seemed to be asking about bone as it is within the human body - referring first to a mutation. I welcome any corrections to the density figure though, I don't want to give a misleading answer. – Ludo May 30 '17 at 8:40
• I checked with another source, this interesting post, and found it to match closely with your calculation: a median cortical (mineralic) density is 1.15g/cm³ and a median trabecular density is an astonishing 0.3g/cm3. So the weight could range from ~23kg (solid-massive) to ~6kg (spongy). – dlatikay May 30 '17 at 10:29

From the disease itself, unlikely.But with genetic engineering yes.

There are mammals that had bone armor, the giant ground sloths(as well as other Xenarthra) had subcutaneous bone armor(osteoderms). Sloth armor is often referred to as biological chainmail. Armadillo and glyptodon take it even further creating a much more rigid bone armor, gaining additional production at the cost of flexibility.

• Quadrapeds have the advantage of a relatively broad and flat back and flanks to present to predators that are ideal for plates of bones. Such structures would severely compromise the movement of primates, which is why few if any have been discovered with them. – Isaac Kotlicky May 29 '17 at 14:32
• You would want a ground dwelling primate: something like a baboon. But the best defense is a good offense and the thing about primates is that their group offensive is one of the best there is. Five male baboons who are sure of each other can drive off just about any predator. Armor of this sort I think would slow down a primate-style offense. – Willk May 29 '17 at 15:18
• If it's a genetic disease, armor plating could evolve from it, however, given enough generations. – liljoshu Dec 21 '17 at 17:50
• not likely with how it work, it is about ossifying any injured tissue and quickly becomes lethal without heavy medical intervention once triggered. something has to make it into the next generation before it can continue to evolve. Although it could come later as it continues to evolve after genetic tampering has been done to cure it. – John Dec 22 '17 at 1:43

I am please to report that the subject has been positively responding to the gene therapy. The real breakthrough was using CRISPR to edit the ossification gene to activate only upon external oxidative scabbing rather than internal inflammation. The platelets seed an osteon at the site of the wound that develops into a sesamoid bone. As a result of picking at their skin, subject has developed bone studding over the outside of their body. These sesamoids have a higher than average ratio of compact to cancellous bone tissue. While the development of this lamellar bone is slow, it is exceedingly durable.

In an interesting development, where the sesamoid bone meets the skin a second collagen coat has developed. Rather than the usual alternating parallel sheets of collagen, subject seems to be developing "woven" patches that function much like kevlar with the bones embedded in this matrix. This appears to allow a much more efficient dispersal of impact, functioning much like the recently deployed Dragon Skin vests.

While the density of the bone does add to the subject's weight, it has not seemed to slow them down. Additionally, the nature of the bone plating does not seem to impede flexibility or range of motion. We estimate that when fully optimized, the exoskeleton and energy dispersal system would theoretically be capable of at least a Gigapascal of compressive force (a sixfold increase) while simultaneously minimizing exposure to the more fragile tensile or shear forces. At that point, the dissipating collagen mesh should be able to disperse the force of heavy weaponry without damaging the internal organs of the subject.

Unfortunately, test subject has proven overly belligerent and have begun to grow bone "claws" as a result of scraping at the walls. They've hospitalized three guards this month.

### Below is an updated schedule of Project Anthromegalous:

Subject Armadillo - Bone exoskeleton. Proof of Concept. Scheduled for demolition

Subject Bison - Genetic enhancements for increased physical performance