In my story there will be animals that are incredibly strong and resistant to injury. To better understand how to design my creatures, I'm asking for help understanding how to make the Eurasian Brown Bear (common in Europe during the 1200's) more resistant to medieval weaponry.

  • No magical answers.
  • Technology from the year 1200.
  • Changes to the bear should be evolutionarily defensible. (Read that as "it makes sense that such a fictional creature could evolve naturally based on the actual evolution of creatures on Earth.")
  • A single shot from any bow/crossbow of the period should not be capable of killing the bear.
  • This question considers the bear's defense, not the bear's offense (I may ask that as a separate question). In other words, while the need to dodge longer claws might make the bear harder to kill, that technically isn't a defense against the weapons of the time, and therefore doesn't answer my question. (So say we all...)

Question: Given these conditions, what changes to the Eurasian brown bear would make the animal substantialy more difficult to kill?

Best answer conditions:

  • The best answer will look beyond the ordinary or obvious (e.g., "thicker skin") to consider the bear's entire physiology.

  • The best answer will consider unique examples of actual evolution as enhancements (e.g., a rhinoceros' horn) but must justify how those enhancements would improve the bear's defense against early medieval weapons.

  • The animal described by the best answer will still be perceptually a bear. (shaggy, walks on all fours, likes salmon). In other words, if the creature were drawn, a child might say, "that kinda looks like a bear...." (This is intended to avoid answers that could be interpreted as, "don't use a bear, use a rhinoceros.")

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    $\begingroup$ You might want to check out my old question Could a creature evolve a biological “bulletproof vest”? as well. It's not the exact same premise, but you may find some of the answers helpful. $\endgroup$
    – user
    Jul 14, 2018 at 6:28
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    $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – James
    Jul 14, 2018 at 23:37
  • $\begingroup$ This will be be opinion based! I say that because: In order to make the evolution make sense any changes you make would effect every species. So you are talking about something different then a bear! It wouldn't be a bear at that point! $\endgroup$
    – Cbm.cbm
    Jul 16, 2018 at 11:24
  • $\begingroup$ Hello P.Lord! I now have 22 hours to award the bounty. Or, more accurately, you have 22 hours to award the bounty. I'm going to give it to whomever you choose as the best answer. Please remember the conditions for the best answer in your post and have fun! I'll come back in 20 hours or so and award to the checkmark. $\endgroup$
    – JBH
    Jul 17, 2018 at 20:00
  • $\begingroup$ @Cbm.cbm, "priarily opinion-based" has a different meaning here than everywhere else on Stack Exchange due to the creative and fictional nature of the site. From our perspective, POB means "the OP has not provided sufficient explanation for how the best answer will be judged," meaning it's wholly subjective to the OP (not the answerer!). Remember, we expect to answer questions about magic.... $\endgroup$
    – JBH
    Jul 17, 2018 at 20:02

21 Answers 21


I can think of something that might from an evolutionary standpoint give you a better armored bear.

First, lets talk about the armor. It will come from 3 layers.

1) Thicker Skin Yeah, this is kind of a gimme. More dense skin is harder to pierce and will help to dissipate the penetration power of crossbow bolts and simpler spears

2) Dense Fat Layer More energy disipation and it also means that anything that gets through still has more distance to travel to get to vitals.

3) Closer and Heavier Ribs This will make it harder for broad bladed spears to get through to the vitals underneath.

How to get there? You only need a few changes to their habitat and ecosystem.

1) Lots of Spiky undergrowth Animals will evolve naturally to be resistant to sharp things in the environment. Look at how thick an elephant's hide is and Look at acacia trees. There are a lot of thorny trees like acacia, Mesquite, and so on. Make those kinds of trees a bit more cold resistant and put them in the bear habitat. Thicker skin will be necessary to make sure those long nasty thorns don't penetrate with irritants and potential infection.

2) Cold Fat is a great insulator. Cold would necessitate a thicker amount of subcutaneous fat. The defensive porperties would be a by-product.

3) Wild Boars The Bear would have to compete with another omnivore and possible food source. Wild boar have the nasty sharp tusks that can pretty much gut other animals and they are low to the ground. This is how the Bear gets a better armored ribcage from evolution. If the bear is going to hunt these beasties as a main food source, he needs to be very tough to deal with another fast, tough, and dangerously armed animal. The ribcage will help the bear fight off a charge from a 600lb angry pig with tusks. So up the boar population in the area.

These changes are going to make a bear an even more formidable animal. Sure, a crack shot from a crossbow might get through, but it would be pretty unlikely. The heavy bear hunting spears of the time would be harder to use because as you taper the point to get through the ribs, you make the spear point weaker.

It's not a perfect armor, but I think it would be plausible from an evolutionary standpoint.


Social changes:

I don't think that any physical changes are necessary to make bears more resistant to medieval weaponry. They are absolutely fierce, 600 pounds, with long claws, and an absolutely devastating swipe and bite. If you put a single soldier vs a single bear, I would probably bet on the bear.

However, they are solitary animals, and live mostly alone. The tolerate each others presence for purposes of procreation, and feeding when food is abundant.

Now give them a social, pack like structure, the ability to communicate and cooperate like wolves, and they become a terrifying foe. One bear is dangerous, 2 bears, twice as dangerous. 3 bears working in cooperation would be terrifying

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    $\begingroup$ +1 for 'bears are already pretty resistant to medieval weaponry. What we need is more bears.' $\endgroup$ Jul 11, 2018 at 14:32
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    $\begingroup$ Not only will pack behavior make bears more dangerous in the immediate, it would also make them more dangerous in the long term. Competition between pack members creates an intelligence arms race. Furthermore, Bears already exhibit problem solving techniques and tool use in hunting. With this in mind, social bears could be a real nightmare. A dangerous, tool using, highly social omnivor? Who does that remind me of... sciencemag.org/news/2016/04/… ncbi.nlm.nih.gov/pubmed/22367156 $\endgroup$
    – Dent7777
    Jul 11, 2018 at 20:04
  • $\begingroup$ The reason why bears evolved that way is because they are solitary animals. If they would be a pack animal they would have evolved differently! $\endgroup$
    – Cbm.cbm
    Jul 16, 2018 at 11:28
  • $\begingroup$ @Cbm.cbm Yes, they evolved as solitary animals for a number of reasons: 1. their food sources can effectively be gathered individually. 2. Their metabolism allows them to store calories from spring through autumn, then hibernate through the winter. They have no need to cache, store, or share food sources. 3. They are an apex predator that happens also to be an omnivore. However, none of these are in direct opposition to forming a pack. Fishing salmon can be done more effectively as a group, Hibernation caves would be better with sentinels, and could store the packs extra food. $\endgroup$
    – Nate White
    Jul 16, 2018 at 15:33
  • $\begingroup$ @NateWhite Forming a pack means having many bears in the same hunting grounds. This introduces competition for food. I doubt you could have pack-forming bears without increasing the number of huntable animals in the area too, basically multiplying the amount of all animals by some number. $\endgroup$
    – Orphevs
    Jul 16, 2018 at 17:11

Evolutionary Problem

You have a big problem.

Ask yourself this question: What type of animal eats armored bears for breakfast?

The only way I can see a bear gaining armor via evolution is if they have a predator.

If you want armored bears to make sense in your world, you will need to introduce an animal that is a natural enemy of the armored bear. A dragon makes sense; your bears could love dragon eggs. But, a beaked T-Rex with feathers would also make sense; the beak evolved to tear off the armor easier.


The Armadillo type of natural armor makes the most sense.

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    $\begingroup$ +1. I wonder if just keeping the SabreTooths around and maybe enlarging them a little would be enough evolutionary incentive for bear armor. $\endgroup$ Jul 10, 2018 at 21:36
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    $\begingroup$ This is a good first start, but bears are predators, not prey. The question probably should be 'What type of animal would a bear want to eat that is so tough to kill it needs armor?' $\endgroup$
    – Ton Day
    Jul 11, 2018 at 7:54
  • $\begingroup$ I don't how much change of the world in general is allowed. But the 'predator' could be a tribe/race of elves/trolls/orcs/whatever in the environment. They hunt bears with their spears and live their since billions of years (long enough for the tribe to have evolutionary impact) $\endgroup$
    – Sip
    Jul 11, 2018 at 14:05
  • $\begingroup$ A possible alternative to a predator of the bear could be prey fighting back against the bear forcing it to develop armour. If deer would not just run away, but every deer and hart would fight back, this would force bears' evolution to create armour to protect them against horns' and antlers' attacks. $\endgroup$
    – Alex2006
    Jul 12, 2018 at 11:19
  • $\begingroup$ @alex2006 - I plan on updating the post such that it explains various evolutionary paths such as: territorial disputes (saber-tooth tiger suggested by HenryTaylor ), food competitor (griffon), guarded food (dragon), food that fights back (unicorn) - your suggestion, and the occasional predator (feathered t-rex with a beak). $\endgroup$ Jul 12, 2018 at 12:43

Give them human-level intelligence and grasping ability (which does not necessarily require opposing thumbs). They will be on par with humanity when it comes to warfare, and thus will be much, much harder to kill. They will actually have the advantage for being tougher than us.

But why stop there? Add a symbiothic relationship with sharks...

Just because

... And these bears will be giving humans a good run for their money.

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    $\begingroup$ Lol, great drawing but not quite close enough to bears for me :) $\endgroup$
    – P.Lord
    Jul 6, 2018 at 16:53
  • $\begingroup$ I am being serious. Increase in intelligence, paw anatomy and symbiosis are alll things that can bears can evolve under the right ecological pressures. $\endgroup$ Jul 6, 2018 at 17:13
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    $\begingroup$ @P.Lord: if you wanted an example of why this is broad and opinion based.. this answer covers broad, your response opinion based. $\endgroup$
    – Joe Bloggs
    Jul 6, 2018 at 17:22
  • $\begingroup$ @Renan I agree with the inteligence but as stated in the question I want the fundamental role of the animal to be the same. $\endgroup$
    – P.Lord
    Jul 6, 2018 at 17:31
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    $\begingroup$ I'm really tempted to change my avatar to that drawing... $\endgroup$
    – user535733
    Jul 6, 2018 at 19:49

We’re going to need a bigger bear

The most evolutionarily defensible solution is to replace the Eurasian brown bear with a different species of bear that lived at another time in another place. The largest known genus of bear is now extinct. It was the short-faced bear that lived in the Americas up to 10,000 years ago when it died out along with much of the megafauna of the time. Compared to the Eurasian brown bear the short-faced bear looks reasonably similar except for its size. The short-faced bear weighed in at nearly 1,000 kg. That’s over 3 times the mass of the 300 kg brown bear. Standing on 4 legs it would be 5-6 feet high capable of staring down would be hunters at eye level. Just due to this bear's sheer mass it should be significantly harder to kill using spear and bow and even more dangerous if you only succeed in wounding it.


It looks like the weapons used at that time in history would be swords, spears, and maces.

So what defends against them for human armor? Metal plate to prevent penetration and leather padding to absorb the blow. Let's convert that into natural defenses, shall we?

Let's fist take the humble Armadillo. It has a distinct feature: natural leather armor. So let's make it much more bony, making it a sort of plate armor. Coupled with the preexisting hide covering it (the bear's natural hide), that should make it resist, although not be immune, to 1200 era personal weaponry.

Of course, thicker bones and stronger muscles would most likely be needed to support the additional weight, but with the side benefit of making this Dire Bear harder to cripple and slightly more resistant to damage from human weaponry.

Using this path, you can keep all classic bear features (fur, 4 legs, snout with pointy teeth inside, same diet but higher in calcium and in sheer quantity, etc.) while hopefully making it a reasonable bear mkII.


First, I will have a look how bears were hunted in that period.

Bear spears were used for the hunt of bears in Russia as soon as 1255. Military use of this weapon dates back as far as 1149. Source: Wikipedia
These spears hat a tip with a two-sided blade and some sort of crossguard to prevent the weapon to get thrusted too far into the flesh of the animal. Multiple hunters used those to kill the bear after it got cornered by dogs.

I could only find some other, seemingly high risk types of hunting methods, of which none is relevant for this question. (E.g. angering a bear, climbing a tree and then hacking of the paw of the bear when it tries to climb after the hunter, and so immobilizing it).

Now, how would a bear defend itself with a natural body armor or otherwise agains a spear? I got some ideas:

  1. Its hair resembling whalebone:
    Whalebone is, in multiple layers, really resistant against alot of things going against it with great force. A blade may even break if it is thrusted against it. Pro: Very resistant against attacks. Con: Very heavy, and unlikely to evolve.

  2. Better senses:
    Bears have not the best eyesight, and only an average hearing. Hunting relies on getting the animal into a situation where it cannot escape. If the bear has better senses, it may realise sooner how it could escape or fight back efficiently. Pro: Better awareness = harder to hunt; could evolve naturally without alot of handwaving. Con: None I could fathom.

  3. Living in herds:
    This may sound lame, but imagine a group of bears, animals which weight multiple hundret of kilos each. They will defend each other, and you do not really want to fight a group of bears simultaneously... Pros: An unstoppable force of nature from which every sensible hunter will run away from. Fast. Con: Large predators only seldomly form herds or packs. It would have to be a large change in behaviour to get a solitary animal to do this.

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    $\begingroup$ Lions are big predators that operate in packs. But they also hunt large prey, which is probably the main thing bears would need in order to group up. $\endgroup$
    – Erik
    Jul 11, 2018 at 7:38
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    $\begingroup$ A con for "Better senses" would be the processing power required to take advantage of those senses. That would require a change in skull size or a reallocation of brain functions. Both are fun tradeoffs on the evolutionary timescale. $\endgroup$
    – Cort Ammon
    Jul 13, 2018 at 14:37

The weapons available in 1200 mostly rely on piercing: arrows and/or blades.

To make a bear more resistant against them, the first idea to have a thicker layer of fat under the skin.

When dealing with an arrow, the thicker fat layer would dissipate some if not all of the kinetic energy of the projectile away from vital organs.

When dealing with blades, it would require a larger effort from the blade owner in order to reach vital organs, and I doubt an angry bear is a place where people like to indulge for long times, considering the possible interaction with its claws.

A thicker fur would also go in that direction, of keeping kinetic energy away from vital organs.

Then also an increase in size would help fighting those pesky humans. Considering that humans would be surely be aided by dogs in their hunt effort, all the above points are also helping against them: thicker fat layer and fur make dog bites less dangerous, and bigger size can be advantageous, too.

Shortcoming of these changes is that warm climates may become less suitable for such a well coated bears, shifting their habitat further North.

To top this, add social behavior, such in wolves or lionesses: it will increase the chances of spotting an attacker and would help protect the individual in a group.

Cons is that the pack would need a larger territory to have enough energy income.


Accelerated evolution 101 - the human solution

The bears need some changes in eyesight, habits and socialisation. These changes are:

  • Excellent night vision
  • Symbiotic working relationship with humans
  • Willingness to wear barding (provided by humans)
  • Trainable to patrol a set area (its territory)
  • Completely nocturnal, returning to human-protected caves during the day
  • Somewhat active during winter (instead of complete hibernation)

Individual bears have been trained for centuries to work in entertainments. Now compare a sheep, cow, goat or dog from 1000 years ago to a modern example and imagine if the same breeding program efforts had been put into bears by some European society in order to create a guard animal. The bear would roam their specified "territory" (which is far enough from where the livestock are penned for the night), knowing that they can eat anything or anyone they catch out there but they will get a feed on their return anyway provided it is before dawn. It may be justifiably argued that dogs, geese and other animals were already good guard animals, but in most cases they alerted the humans that there was something to be done. If there is a 250-480kg bear on patrol, the humans just need to pick up some grisly souvenirs the next day and hang them out as warnings.

So how does this meet the OP requirement:

  • No magic - check
  • Year 1200 tech - humans have been breeding animals for millenia
  • Evolutionarily defensible - bred for a particular purpose. Eyes may not change quickly to include more rod cells, but breeding can select for good sense of smell and hearing
  • No single shot kills - shooting over open sights in the dark at an armoured bear in the forest? Which you somehow spotted before it detected you? On its home territory? Extremely likely to survive. And bite your head off. The key is the tactical employment of the bears (ie not using them as dramatic looking units to assault a fortified wall in some pseudo-historical fantasy wargame).
  • The bear's offensive capabilities are not a factor - check, I have not worried about them. They are already good enough for the purpose.

These bears may be bred to be slightly smaller than the standard European Brown Bear - it is not critical to their function; it will make them easier to feed during lean times and it makes them harder to detect and harder to hit at night.

Finally, there is a human constitutional change that would be required for the society existing in symbiosis with its nocturnal guard bears. There must be a provision that:

A well-regulated militia being necessary to the security of a free state, the right of the people to keep and armour bears shall not be infringed.

  • $\begingroup$ The right to arm bears would make them a fearsome foe, so fearsome as to be unbearable $\endgroup$ Jul 13, 2018 at 13:25

IMO the defensive requirement is excessively artificial, because it seems to assume that defensive measures are never offensive ones and vice versa. The obvious answer to that is the tired old cliche 'best defense is a good offense'. Also, effective solutions are likely to result in bears no longer perceptually being a bear.

Objections aside, here are 2 non-mutually exclusive answers:

Chameleon Bears

The bears are able to change their appearance to blend in with their surroundings. Optionally, they are able to regulate their body heat and metabolism as well. Avoiding detection aids bears in hunting prey on land and also in turn keeps them from being hunted by humans. If anyone trespasses on their territory or strays too close to their cubs, chameleon bears can proactively deal with the problem by stalking the intruder before giving him a good mauling.

I know this doesn't directly make them more resistant to medieval weapons, but it takes the approach of there being no target to attack at all. Why would bears have hide if they weren't able to hide?


Like porcupines, the bears have an array of long barbed spines on their back, and optionally also secrete a strong toxin that coats these spines. This one does directly answer the question because it would be very hard for spears and arrows to get past this extra layer at all.

Since we're talking about bears and not porcupines the spines would be scaled up appropriately, so they could probably rival the length of spears that humans wield. Having this adaptation also allows bears to utilise the hedgehog defense. A mother bear can defend her cubs this way as well, by hugging them real close before curling up into a ball.


Your bearcupines could have their paws adapt to be able to grasp their spines, and the intelligence/instinct to wield their spines both as a spear and a javelin. They can now hunt animals and fish the way humans do. It also allows them to fight the humans on equal-ish terms if they have to. Spearmen? Bear spears you back. Archers? Bear returns fire with thrown spines. With the strength of a bear behind it, being hit by one of these 'javelins' is probably closer to being shot by a ballista.

If that's not enough for you, throw in chameleonic skin as well.

  • $\begingroup$ Bearcupines. That's absolutely brilliant. The downside would be the nutritional cost to grow and replace the spines. For example a deer's antlers represent a years worth of nutrient. Porcupine quills are modified hairs, so much less resource intensvie than horn/bone, but still, this would require a lot of additional calories for the bear. $\endgroup$
    – Nate White
    Jul 12, 2018 at 20:58
  • $\begingroup$ @NateWhite Yeah, beacupines are definitely the more fun but less practical option due to the energy cost required. Chameleon ninja bears would be the more workable option here. $\endgroup$ Jul 14, 2018 at 21:16

Reason for evolution

First you need to explain why your bears did evolve to resist arrows. You could just say that they evolved that way because of the humans hunting them, but this might seem a bit too short in terms of evolution. A better way is to find a natural cause for this.

Enter the dart-tree

The dart tree (known as Hura Percutans) is a cousin from the existing Hura Crepitans, whose fruit is explosive. The differences are power (100x more powerful explosion) and shape of the seed (shaped as a dart). The Percutans fruit will explode more or less randomly and send killer darts in all directions. A dart will pierce through a normal bear. Also note that this tree is dangerous for neighbouring trees, so it tends to create clearings around it in forests.

Evolution to survive

The bears needed to evolve a bit to survive this. Basically they did two things:

  • Augment resilience
    • Duplicate organs that are vitals. If one of the heart is struck, the other one will carry on.
    • Distribute organs. Two hearts not too close from each other are less likely to get both hit at the same time
    • Augment resistance to infections and cicatrisation and healing capacity, so even if a bear is hit, it can survive
  • Reduce exposition
    • Develop a strong preference for dense forest: clearings might indicate its presence. Also dense forest does not let projectile go through very far.
    • Maintain a low profile. Bears started to walk closer to the floor, much like crawling. They are less likely to get hit this way.

Advantage against humans

These evolutions gave the bears massive advantages against bow and other similar weapons:

  • It is very difficult to stay far enough from a bear and at the same time having a clear enough sight of it to shoot it in a dense forest. The result will be that you need to get much closer than on open ground, and hence reducing the advantage that a long range weapon is giving you. Most likely the bear will surprise you from behind a tree and maul you. Especially a crawling bear.
  • Even if you can hit it, it is more likely to survive and either to charge you or to escape.


Good luck for your bear hunting session in this dense dark forest, full of crawling bears and killer trees. Have fun.


Everything is made of Keratin. From the hair of your forearm to the rhino's horn like you mentioned. Your nails and the foot of a horse.

Did you also know that every hair on your body comes along a tiny muscle system? That's why they raise when you're cold or scared. Of course, we being almost naked compared to a dog in terms of fur, don't have much use of that system.


A bear that evolved with a thicker fur, in comparison to a goat's horn in density and strength could have also evolved with a better muscular hair moving system. While having separated units of really thick hair would not do it's justice against a bolt, if the contraction of said muscles would stiff up that section of the body that was in danger and grouped the fur in a certain pattern, that would make a bold and strong scale like defense.

Having that system activate by will or instinct would grant the bear a movable and flexible fur that would still look like a bear. And of course multiple strikes against its fur would eventually breaks the keratin... but it grows back! It's in all senses still just fur!

If you have a problem with the active use of said defense, remember, you can't get an off guard bear with medieval technology. His hearing and smelling abilities surpasses easily a normal human being's.

  • $\begingroup$ "remember, you can't get an off guard bear with medieval technology" Sure you can, you sneak into their cave while they are hibernating. $\endgroup$
    – Nate White
    Jul 12, 2018 at 21:00

As has already been mentioned, unaltered bears can already survive a shot from an arrow or bolt. Aside from thicker hide, how do we make them even better pin cushions? Two prongs.

(A) Make the bears capable of taking more hits.

Super fast blood clotting. Some of the gigantic tortiouses of the galapagos were tragically famous for their blood clot speed: sailors would keep the animals on board as a preservable food supply, cutting the poor, still-living creatures apart one limb at a time over the course of journey.

Superb immune system. Crocodiles are well known for their excellent resistance to bacterial infection. They frequently endure large cuts, even limb loss, and yet never end up with infections despite the fact that they live in bacteria-rich swamps.

(B) Make the bears capable of taking hits in more places. The ability to absorb lots of arrows to the chest without dying still won't protect you from an arrow that makes a direct hit with a vital organ. Some suggestions:

Organ redundancy. Super healing isn't much use if you get hit in the brain, unless you have a backup brain in your spinal column!

Every organ has liver-like regenerative properties. This isn't a perfect fix, because a bolt to the liver is definitely no picnic, but combined with the other traits, this could be a real boon

Evolutionary Origin This really depends on your world. If you want bears to be specially adapted to resist medieval human armaments, the best explanation for these adaptations is that they evolved over the course of thousands of years of combat with medieval humans. Note that I say "combat" and not "being hunted": if the bears were merely hunted for thousands of years, they might just become smaller, more shy, sneakier - things that probably don't suit your narrative. On the other hand, a population of bears that live in an area where the only food is either humans or livestock, where all vegetable forage and prey animals have been deplete, then they might be forced to evolve the ability to go toe-to-toe with iron-clad warriors. Note that the Panda evolved to be completely vegetarian - it's not enough to merely deprive your bears of meat food to drive them down this path. If your humans have not been at this technological level for thousands of years, contrive another creature in the ecosystem that might simulate human-weapon wounds. Perhaps these bears evolved in a wasteland of undead, fending off legions of heavily armed skeletons?


I'd have a suggestion, similar, but different to one by @KerrAvon2055.


Bears were hunted by humans for millennia. Because of very useful bear fat, (believed, never true) magical powers of bear heart, early-adopted beekeeping or at least honey collection from wild bees, usage of bear claws for impromptu weapons, you name it.

When mammoth died out, humans were already hunting bears. Modern European bears date back for around half a million years. We need to increase this span or to make humans hunt their predecessors.

Make humanity exist for ten millions years instead of roughly a million. Make prehistoric bears also bears from which the nowadays bears descend.

We might also need a longer medieval period. Say, the classical fantasy medieval times (but without magic) span for few millennia. But this is a more boring and less productive options. We need millions of years of stone-spear bear hunting.

Maybe, some kind of repeated regress of humanity to early stone age would help. Best, something that not affects bears a lot, like a repeated mild climate change cyclus that strikes the fur-less apes, but not furry bears.

Summarising, as bears were hunted for such a long time, but

  • humanity never managed to rot bears out;
  • both humans and bears adapted to the hunt;
  • evolution is a bitch;

and hence bears have developed some kind of an evolutionary mechanism to increase their chances.

This could have been:

  • the (boring) more strong hide;
  • the spikes a la *sauria;
  • venomous blood;
  • better reaction and longer arms;
  • full-carnivore mode to pump up activity and reaction time;
  • pack mentality a la wolfs;
  • thicker fat layer, so spears have troubles reaching vital organs;
  • instinctive fear of human-like shapes, such as bipeds in general;
  • you name it.

You will need to have large sub-arctic prey. Then make bears hunt that prey in packs.

Eurasia has lost its large sub-arctic prey (such as mammoths, wooly rhinos, etc) due to hunting and ice ages. As was already said, bears are pretty dangerous already, but they are solitary and choose to leave humans alone.

You can make them hunt mammoths and whooly rhinos in packs, which will make them also much more dangerous to humans, and also suitable for domestication to be used as war beasts.


Okay so why are the medieval people killing bears? Possible reasons:

  1. To eat them, either for actual nutritional value or because bear meat/fat/gall bladder is alleged to impart good luck or special powers or cure certain diseases. The way around this one is to make the bear's flesh toxic in some way. Some lizards have toxic green blood, which might be to prevent them getting malaria. If the chemical in bear blood or bear muscle is toxic to humans as well as to whatever parasite the bear is trying to kill, then we'll steer clear of them. Alternatively, like the hawksbill turtle eating toxic sponges, the bear eats something and accumulates the poison in its flesh. This could lead to all sorts of folklore about it being unlucky to hunt bears (as well as them being bad tempered and dangerous).
  2. Bears kill our livestock and eat our crops. We want rid of them. If they are too tough to hunt, we'll revert to poisoned bait, traps and the like.
  3. Because killing a bear proves your manhood. I don't think there is any way to stop people trying to do suicidally stupid things in the name of machismo, no matter how tough or dangerous the bears are.

So, toughening up the bears... They no longer hibernate. Instead they have to survive the whole winter outdoors. They'll need a number of physiological and anatomical changes to do this:

  • Really thick fat layer. Real bears build up lots of fat to sleep thru the winter - as nutrition. These bears need lots and lots more, because they'll be using it up faster as they will be active all winter. The fat is an extra layer of protection. Perhaps it is 11 cm thick like polar bear fat layers - but equally thick all over the animal. So your crossbow bolt has to penetrate more than 11 cm before it hits muscle, bone or vital organ.
  • Thick skin is also a good insulator against the cold. So above the fat is thick skin.
  • Mammals have two layers of hair - ground hair (down fur) and guard hairs. An air layer is trapped between skin and fur to keep the animal warm. Here's a diagram of polar bear fur and skin. Perhaps your bears are unique and have additional types of hair and their pelt is a sandwich of several layers of fur and several air layers for maximum insulation. Again, this means the depth your blade or bolt has to penetrate becomes much deeper than for a normal bear.
  • To accumulate all this fat, they have expanded their diet to include more brains and bone marrow. Not just crunching up rabbits and salmon like regular bears do - these guys have evolved the bone crushing jaws of spotted hyenas, to crack open the toughest skull and the strongest leg bone. If they can crush a bison leg or skull and not worry about bone splinters in their mouth, then they can crush the wooden shaft of a spear and not worry about wood splinters.

So people who stick a boar spear in a bear may not get the blade deep enough to inflict a serious wound, and their spear will be bitten in two shortly afterwards!

This does mean that there will be a time of year - early spring - when bears are easier to kill. They'll have used up lots of their fat reserves, and will have moulted their thick winter pelt for a lighter, shorter summer fur. Also bears which live in warm places will be accumulating fat to get through the dry season, not the cold season.


Bears usually were hunted like how boars were back in medieval times, with huge spears in hunting parties, with dogs to flush them out. This is because (believe it or not) bears were pretty big and scary animals. Being that they were pretty hard to kill, you wouldn't have to make very many changes.

Bears have extremely thick fur already, which along with it's fat, reduces the kinetic energy and penetration of attacks effectively. You could could say in your world that they produce some sort of oil or resin that makes their fur matt and thicken. This could make the hair super hard and layered, making it function like full body armor. The substance coating it would hold the hair stiff against attacks from spears or broadswords. You could explain it by saying that it is waterproof, and so bears evolved it in order to be able to dive into rivers quickly, get food, and leave without all the water weighing them down, or something along those lines (maybe they have fast predators?).

You could also couple by increasing the layer of fat in their skin to make them bigger and tougher to kill, and it keeps the organs from harm if a spear stabs them (harder to reach heart).

Like I said, bears already are extremely hard to kill (as stated here https://en.wikipedia.org/wiki/Bear_attack#Fur) and all you have to do is augment their best natural defense.

If this isn't enough, you could couple it with Nate White's "move in packs" method.


Very wooly floofy, bears. Thick tough hairs cover their body and grow long into an afro-like mass covering their body. Like the fur of a bison but 10x thicker and fluffier and tougher. They don't shampoo and condition it, so after living their outdoor lifestyle eventually this is caked in mud which stiffens it even more and adds mass. Arrows hit this 14" layer of muddy thick floof and lose most of their energy. Even after being told, swordsmen still underestimate how deep the floof is, and just end up hacking some of the floof off. They're scared, they aren't sure where in that mass the actual body is, and they don't want to plunge their sword deep in there and have it get stuck and lose it when the bear lunges away. Spears are still the best weapon. After all, how do you defend yourself from a man that attacks you with a pointed stick? But the floof still gives a fighting chance. The bears aren't often holding still while fighting, and when a spear enters the floof, the moving floof is likely to push it off target. You have to be really strong and unwavering to hold your spear on target as it pushes through the floof. Most spears miss or only hit glancingly on the bear's actual flesh, and then are likely pulled out of their owner's hands. During battle the bears will sometimes shake like a wet dog, flinging the accumulated weapons out of their fur and outward in all directions.


Physical, mechanical defense against weaponry is going to be hard to defend in evolutionary terms. Physical structures are energetically expensive to develop and maintain, so there needs to be a good reason for them to exist, but in terms of avoiding intelligent hunters behavioral changes are probably more plausible. But, if you're willing to suspend disbelief just a bit...

Crumple Zones

Most modern cars have specially engineered regions which are designed to absorb kinetic energy and dissipate it, rather than passing it on to the entire structure of the car itself. That way you have one section that, while it will be damaged badly, will protect the overall structure from bearing serious damage. If the bears have regions of some combination of bone, muscle, and/or some sort of shatterable armor (like chitin in insects, or the armored plating of armadillos) which are arranged correctly, the force of a projectile could conceivably be bled away such that the bear can handle it. Additional shots to the same region would be bad news, though.

Grooves and Ridges

This adaptation would involve some sort of hard or tough structure on or beneath the skin which has patterns of raised and lowered sections which redirect the force of a projectile elsewhere. If a crossbow bolt hits straight-on, bad news again, but if the angle is even slightly off the grooves can "slide" the arrow off to the side. Depending on how effective the physical structure is at resisting being punctured (bone and tough, leathery skin would be different in how well they avoid being punctured, torn, or scored) this could very well prevent the bolt from blasting inwards to any meaningful organs.

An important feature of this if the structure is under the skin is that blood loss needs to be dealt with. Skin that is lightly vascularized, or adaptations that promote rapid clotting of some sort would help.

Rapid Clotting

Even in the case of an actual bear, shooting one with a crossbow is more likely to really, really anger it than kill it outright. Blood loss over time is a more serious concern, especially if the bolt hits a major vein or artery. A bear which can quickly slow the bleeding will have more staying power. Such an adaptation would have implications for internal blood clots (think brain aneurysms), which would reduce the creatures' survivability, but you can get around those. The clotting factor may only activate upon exposure to external air, based on some carefully-maintained internal chemical condition, for example.

Low-Density of Important Structures

If most of a bear's mass is not strictly necessary for it to live, then a bolt is less likely to hit something critical and cause it to die. This is similar to DNA-- most of the DNA in a human doesn't code for any proteins and is just sort of "there". But when exposed to potential damage (like mutations during replication), just as a matter of probability those are more likely to affect some region which doesn't code for anything, and so the error is irrelevant to the survival of the larger organism. If a bear's body is mostly structures which, if hit, wouldn't destroy its ability to function or cause it to bleed out, it would be much harder to take one down with a projectile.

Redundant Structures

This one may be the hardest to defend from an evolutionarily plausible perspective, but redundant structures would mean that even if one were destroyed its function would still be carried out. It's hard to imagine a situation in which having, say, two hearts would be worth the additional energy beyond having just one. But perhaps they work in concert (sort of like having two lungs), where losing one makes you less good at surviving than having both but isn't necessarily life-ending.


Bears are already pretty resistant to modern weapons, unless you get pretty lucky with a 1200's crossbow you're just going to aggravate it. You'd like it more resistant yet and still a bear so, you can give it: thicker fat, thicker preferably matted fur, heavier bones, or just make it all around bigger. You could mess around with the internal structure somewhat as well, if you thicken and extend the ribcage down to cover the liver, spleen, and kidneys completely, enlarge the head by thickening the skull and increasing the jaw muscles and thicken the long bones in the same way, expanding the musculature accordingly you have thick muscle over thick bone over all the major organs without making any major changes to how the animal looks except that it will look somewhat fatter.

Some of the material in this question my be of use to you also.


/A single shot from any bow/crossbow of the period should not be capable of killing the bear./

It is extremely difficult to hit the bear. The bear is quick.

This bear is small, lean and lithe. It has converged on the body habitus and lifestyle of its Carnivora cousins. The mongoose genus (https://en.wikipedia.org/wiki/Mongoose) is absent from Europe and so in this world ursids have evolved to take that niche - like weasels and stoats but larger and more powerful. Just as fast. A mongoose can kill a cobra because it is so much faster than the cobra it can dodge its strike, move around and grab its neck.

https://www.youtube.com/watch?v=MqkWQo5JNzE mongoose dodges arrow

View here a mongoose that heard the arrow coming, saw it in flight and dodged. Picture your quick little bear doing exactly that. A single shot is not capable of killing the bear because they dodge the arrow.

I can see the comment coming and so will answer in advance: Yes, if you tied down the bear first then a single shot that hit would be capable of killing the bear.


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