Wild animals like wolves, lions and bears rarely attack people. They behave as though they know humans are dangerous and generally best avoided.

Imagine a group of people traveling sideways in time, to a world that resembles Earth as it would have been had humans never evolved. Thus, the familiar species of wild animals are present, differing from those of our world only in having never been exposed to humans.

How much more dangerous would they be?

I can think of three possibilities:

  1. The knowledge 'humans are dangerous, do not try to eat' is instinctive. Then the animals would be extremely dangerous for many generations until enough of them have been shot to evolve that instinct.
  2. The knowledge is somehow learned. I don't quite see how this could be learned in the life of an individual animal, but if it is, then by hypothesis it could be learned quickly by the animals of the other world.
  3. I've got it the wrong way round. Predators don't use the algorithm 'hunt anything that moves unless you know it's dangerous', they use the algorithm 'avoid unless you know it's safe'. In the absence of positive identification of humans as safe, the animals of the other world would avoid humans just like the ones of our world.

Which of these is the case? Or is there something else I am missing?

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    $\begingroup$ You aren't wrong there is little bit of each, and more $\endgroup$
    – MolbOrg
    Mar 25 '21 at 5:42
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    $\begingroup$ I have noticed that playing children tend to shout and scream a lot. And I wonder if they did that in the Stone Age. Perhaps some predators hearing unfamilar creatues making a lot of noise in one direction would go the other way just to be safe, and the noisyness of children might have evolved to deter predators who were unfamiliar with humans. $\endgroup$ Mar 25 '21 at 17:05
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    $\begingroup$ Might wolves, lions or bears rarely attacking people be more about contact being rare? What might “traveling sideways in time" mean? Doesn’t that suggest you’re looking not about time, but some variation of the many-worlds/multiverse theory? In a world resembling Earth as if humans never evolved, how far back are you going? 4,000 year of written history? 300,000 years of archaeology? What between? $\endgroup$ Mar 25 '21 at 23:24
  • $\begingroup$ "I don't quite see how this could be learned in the life of an individual animal" — maybe it could be passed on inside packs: so if a species tends to live in packs, or however named groups, in certain conditions it could be enough if only one individual has had the experience. $\endgroup$
    – Levente
    Apr 26 '21 at 0:26

10 Answers 10


All of these are true, so it depends on the animal.

First, you have a lot more to worry about than predators; herbivores are often more dangerous than carnivores. Carnivores may hunt you when they are hungry, while herbivores may attack you for just being too close in case you are a predator. Hippo are more likely to kill you than a lion. An elephant in musth will kill you because you are there. Animals with young are particularly prone to this. Of course this is not all herbivores but most of the larger ones.

For predators, it depends on the predator. Large ambush predators like crocodiles are often not that picky; strange food is food, because they rely on ambush they have less opportunity to investigate prey. This is the predator that will be most dangerous to your people, because they don't know what signs to look for.

Most other predators tend to investigate new things before trying to eat them; some of them of course will conclude you are food. Humans are large enough that most predators default to seeing humans as a potential risk to hunt, so spend a lot of time investigating. But some predators are large enough this is not the case; things like polar bears and tigers are large enough they have to learn humans are dangerous. The bigger a predator is compared to a human the more likely it will decide you are worth eating without much investigation. A t-rex, just like a large shark, might nibble just to check, but a human may not survive the nibble.

Humans have the double edged sword that we look bigger than we are, which makes animals wary, but predators and herbivores react differently when wary. Predators avoid, while herbivores may default to "drive it away".

These are behaviors that evolved over and over again in the animal kingdoms, often with no human contact whatsoever. There is every reason to believe these are the behavioral patterns you will see on another planet.

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    $\begingroup$ Herbivores don't necessarily "want" to kill you rather than scare you away. But getting trampled by a herd of cows is not good news for a human, regardless of the cows' motives for stampeding. $\endgroup$
    – alephzero
    Mar 26 '21 at 1:11
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    $\begingroup$ A polar bear is significantly more dangerous than a tiger. It will try to eat you. $\endgroup$
    – Nelson
    Mar 26 '21 at 7:56
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    $\begingroup$ @alephzero I never said anywhere that herbivores want to kill you, in fact I say the opposite that they want to drive you away. $\endgroup$
    – John
    Mar 26 '21 at 15:25
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    $\begingroup$ I don't see how this actually addresses the OP's question. This makes a lot of statements about how animals are here on our Earth, but says nothing about how they would be different if they did not evolve alongside humans. If your argument is that animals would continue to behave exactly as they do on Earth, you should probably make a statement that says so specifically. $\endgroup$
    – Nosajimiki
    Mar 26 '21 at 15:55
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    $\begingroup$ @Nosajimiki there is a huge range of animal behaviors but these are the ones that pose a threat to a human sized animal. we see these strategies evolve over and over again everywhere in the animal kingdom there is no reason to believe it would be different on another planet. But if you want I will say it in the answer proper $\endgroup$
    – John
    Mar 26 '21 at 17:52

It can be any of them, depending on the environment where the animal is grown and the animal's own behavior.

Take for example the dodo: living in an environment with no predators, it didn't have the flee instinct, thus it was easy to capture. So easy that it got extinct. Or the pigeons which are being eaten by catfishes, not being used to avoid threats coming from underwater.

On the other hand, curiosity might lead the animal to investigate what that funny, fur-less and two legged beast is. For a predator that usually means try to give it a bite. That's what most of the sharks do when seeing a surfer or a sub.

Also note that for a predator approaching an unknown being, the being starting to run away usually triggers the hunt instinct. And it takes a lot of cool to have a beast the size of a lion or a bear sniffing around you and not flying away.

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    $\begingroup$ See the giant pacific octopus, which is known to be a naturally intelligent and curious animal: it's already been shown that their first instinct is to be defensive, while once it realizes the weird guy swimming in front of it isn't a threat it will start touching it all over with its tentacles to investigate. $\endgroup$ Mar 25 '21 at 12:49
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    $\begingroup$ Uhm, sharks don't really randomly take bites out of surfers. This almost never happens outside of movies, giving even more credibility to the idea of them playing it safe $\endgroup$
    – Hobbamok
    Mar 25 '21 at 14:54
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    $\begingroup$ @Hobbamok, what I have read is that they either poke the human if they happen to be at the same level, or bite when they are attacking it mistaking the surfer for a seal as seen from underwater. In that case they usually "spit it out" because a seal is much more fatty and tasty than a surfer. $\endgroup$
    – L.Dutch
    Mar 25 '21 at 15:31
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    $\begingroup$ "That's what most of the sharks do when seeing a surfer or a sub." No. Sharks bite surfers because they look like their usual prey when looked at from underwater, not because they are curious what that thing they don't know tastes like. $\endgroup$
    – Polygnome
    Mar 25 '21 at 15:36
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    $\begingroup$ @Polygnome It's a little of both. Studies of sharks have shown they'll bite at something new they think looks good, but they aren't as enthusiastic about it as when they've mistaken a swimmer for a sea otter or a seal. $\endgroup$ Mar 26 '21 at 1:18

Generally Option C

As far as predator go, the "hunt" kind (all of the big carnivores on earth atm)are naturally fairly cautious. They don't kill from a distance, they don't catch things in traps which incapacitate them. They have to get Up Close and in harm's way. There's a chance prey could hurt them back, and getting hurt can be a death sentence even if they make the kill. So their basic reaction to anything initially is to be very cautious about it. Now how long they stay cautious depends on the species and the animal. Lions, for example, will get over that shyness fairly quickly if it's just a single weird thing. (think vids of lions meeting drones or RC vehicles for the first time) They know they're in a group of other apex predators who will, to some extent, take care of them if they're injured, so they're more willing to test out new things. Solitary hunters like Leopards are far more risk adverse because they know if they get hurt they're on their own.

Of course there are things humans could do to "give the game away" as it were. Running in panic can trigger chase responses, then the thing finds out the human is a squishy frail bag of food and the jig is up. A predator like a web-building spider or an ant lion is also pretty "grab first, ask questions not-at-all" which is likely based on their hunting style. So if you had a thing big enough to eat humans that makes webs that catch humans it likely wouldn't think twice of eating one in its web.

For herbivores things are much more complicated and again depends on the animal. For instance if you ran across a gazelle who'd never met a human it's reaction once you got close enough would be "Flee in panic." But if you got close to, say, a Water Buffalo or Hippo it's reaction wouldn't vary from what it is now. Which is generally "Trample/gore/bite to death." Basically if an herbivore would get aggressive when hunted it'll get aggressive towards an unknown human which gets too close. "Too Close" bye the bye, is also fairly random and will depend on how the herbivore is hunted and by what. Is fairly slow and lives in the open? You might trigger the fight-or-flight reaction from further away than something which is lots faster than everything which hunts it.

All of the above are, naturally, size-dependent. A 20ft carnosaur of some sort wouldn't think you're a threat at all, and chomp on you just to see what you tasted like. A 50ft carnosaur might ignore you entirely as being too small to be worth the bother. Meanwhile a 50ft herbivorous dino might trample you to death, because you're about the same size as the raptors which hunt the herbivore in packs. Then again, if the herbivore is only hunted by things 20ft tall or bigger it might just ignore you until you actively annoyed it.

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    $\begingroup$ Also note: Humans tend to camp/travel in packs, which also affects things $\endgroup$ Mar 25 '21 at 16:48


There are two cases of predators in the modern world that have no natural fear of humans and well-documented interactions with people: polar bears in the high arctic and oceanic whitetip sharks in the open ocean. People have reported similar encounters with both. With polar bears, polar bears are known to walk towards human activity, wander through settlements in the far north with no fear, and even try to knock over tour busses in the arctic to try and get at the humans inside. But you don't have to take my word for it, here's a YouTube video of a wildlife photographer nearly getting eaten by polar bears, only being protected by a very strong acrylic cage. Polar bears often aren't afraid of the sound of gunfire and don't see humans as dangerous, they see them as food.

Oceanic whitetips are similar. Far out in the ocean, they rarely encounter human activity and hence most don't have much of an innate reaction to humans. They live in an environment with little natural food and as a result they are often hungry all the time and always on the lookout for new food. Oceanic whitetips are insatiably curious, and studies have actually found they're drawn towards sounds of human activity, such as those made when a ship sinks, because they exhibit curiosity towards any novel stimuli in their environment. This is why oceanic whitetips are the number one threat to shipwreck survivors out of any marine animal. Survivors of oceanic whitetip attacks will note that nothing really drives them off. You can punch them, hit them in the gills, and it won't convince them that you're not a worthwhile target. They'll just circle back around and wait for you to weaken enough that they try again. The only real way to get away from an oceanic whitetip is to get out of the area.

The thing that most of the other answers don't point out is that while predators aren't naturally bloodthirsty, they're naturally curious. Predators are highly opportunistic, and as a result they're always interested in a new opportunity that might bring them something to eat. Humans are the same way, it's the whole "can't look away from a car crash" phenomenon. If a stimulus isn't immediately threatening, predators will often investigate it to see what it is. Deviating from the routine is potentially a huge benefit if the animal learns of a new food source it can exploit (this is how man-eating lions, tigers, and bears start). And the way many predators investigate something interesting is with their mouth.

In your situation you would probably have predators investigating the novel humans in their environment out of sheer curiosity if nothing else. Without a fear of humans they won't be conditioned to avoid people. Eventually a predator, most likely a young male or some other individual who are prone to taking risks, would likely eventually try to take a bite out of humans. And if that predator isn't killed or harmed the predators would quickly learn that humans are easy prey. There are cases among large predators IRL where predators learn which prey items are good to eat and how to catch them by watching each other.

The good news is that any real defense would drive the predators off. A predator won't try to attack someone if you figuratively bop their nose hard enough unless they are really starving, and having potential prey that is strange and can bite back is enough to make a predator decide to go bother someone else.

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    $\begingroup$ Indeed, my (hybrid) cats investigate everything new in my house by watching it for a while then slowly approaching and chewing on it to see if it’s food. But if the thing makes noise or moves toward them, they’ll usually back off. Usually. $\endgroup$
    – StephenS
    Mar 26 '21 at 3:32
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    $\begingroup$ "where predators learn which prey items are good to eat and how to catch them by watching each other." Orcas apparently teach each other how to kill sharks and extract their livers. $\endgroup$
    – Michael
    Mar 26 '21 at 15:20
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    $\begingroup$ @Michael Supposedly tigers in one national park in India have learned to trap deer by chasing them into the water. Only tigers in this one national park do it, and biologists think its a learned behavior. They're worried the behavior might go extinct due to poaching. $\endgroup$ Mar 27 '21 at 3:10
  • $\begingroup$ @user2352714 Can you provide a link for that? Sounds interesting. $\endgroup$
    – Cyphase
    Mar 27 '21 at 23:42
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    $\begingroup$ @Cyphase It's in Alan Turner's The big cats and their fossil relatives (1997) $\endgroup$ Mar 28 '21 at 0:53

We are finding in much of Canada with the decrease in hunting and general firearm use that bear and cougar are losing their fear of humans, and we are getting an increase in injury/death encounters. Case a few years ago with a cougar on the edge of the school grounds watch the kids play.

I have done canoe trips where we had bears wander into camp.

While wolves in North America seem to either leave people alone, (or they are smart enough to cover their predation...) in Europe they have a grimmer reputation. As others have mentioned polar bears actively hunt people.

That said, Medieval Europe was characterized by far more fear of predators than actual predation. This came up about a week ago (~apr 20 ) on reddit's /r/AskHistorians. The fear was much greater than the reality.

Larger predators tend to cautious about things that are strange. This can change if hungry, or you smell interesting. The more different you are, the more likely they are to give you room.

Size ratio is also critical: lone predators tend to prey on animals smaller than they are. To hunt animals larger than you are requires group effort. Wolf packs are larger where they prey on moose than where they prey on whitetail deer. Polar bear and grizzly are enough larger that we don't intimidate them. Also, they are less likely to be cowed by our standing posture as they can also stand. (To a coyote, a human is much taller, hence larger)

In places where wolf are hybridizing with coyote we are getting "coywolfs" which are intermediate in size between the two species. They seem to have the coyote's comfort levels of living near humans, are better able to treat medium sized dogs as 'lunch'. At this point they don't seem to have the wolfish pack structure. If you want an interesting sidelight in an urban story, picture a hybrid with wolf smarts and pack stucture, and coyote's 'just at the edge of accurate rifle shot' proximity to humans. Could make the cityscape more interesting.

Small animals are more likely to attack with a 'nothing to lose' attitude. One trapper I know said the only time he's ever been attacked was by a muskrat.

Herd animals are dangerous just because you can get in the way. Having a hundred zebra or buffalo running toward you can ruin your morning. Large herbivores are dangerous. Rhino and Hippo are cases in point in Africa.

Many animals during the mating season are more likely to see you as a threat. Moose are have a rep for aggression when in rut.

Herbivores learn quickly. Look up what the ecological impact on both deer and general riparian ecology was from the re-introduction of wolves into Yellowstone.

Consider: Look how fast dogs learn things. Admittedly we've been breeding dogs that pay attention to human body and voice.


The algorithm animals use is less based on fitting objects into a formal ontology the way we do ("this one is a human, that one is a gazelle"), and a lot more based on salient features that are being perceived in the moment. When it comes to differentiating between danger/prey/not-interesting, the most important feature seems to be size. Other important ones are pattern of movement, sound and smell. There are sometimes additional highly-specific signals that can elicit specific behavior (example for instinctive ones: the red spot on a gull's beak, example for learned ones: a command for a trained dog), but these are species-specific and won't bring you further here.

Ontology-based learning does happen (e.g. once a predator has been wounded by a porcupine, it learns to avoid all porcupines), but I have the impression that the perception-based behavior is usually more dominant for animals. For example, my cat has learned very well that the string on her rod toy is totally uninteresting once caught. Nevertheless, as soon as I wiggle it in front of her, she cannot help but go into a hunting mode. It is even observable how she is not so much using her intellect to decide "now I will play with this toy", but how her autonomous nervous system visibly drives her body, from changing her pupil dilation, up to the typical haunch twitches.

So, it is not especially important that the animals have never seen a human. As soon as they perceive the human, the features observed in this perception will guide their behavior. If humans are of the "proper" size, they can be attacked for two reasons, either because they resemble prey (again observable in house cats, they prey-attack anything in the size range of a mouse), or because they resemble a danger to be driven away (typical in e.g. swans attacking kayakers - but note that the reaction of a Baltic seal to a kayaker is panic, again because of the size, they are rather undaunted by larger and noisier motor boats).

The behavior of the animal will depend not only on what it perceives, but also on the context of the encounter. There is the "aggro radius" mentioned in other answers, its size depending not only on species, but also on the lay of the terrain, the personality on the individual animal, and on its current emotional state. Other factors matter too - meeting a lion pride at dawn, when it is looking for prey, is different from meeting it at noon, when it is holding its digestion break.

Getting to know humans will get animals to learn behavior in some very specific ways, which won't have that much influence on being attacked in general. The closest would be if a lion pride learned to specialize in humans - they are not indiscriminate, each pride has its favorite pray animal, and the knowledge how to hunt for that specific animal is passed down from the adult lionesses to the young ones. The more common examples are the ones where it changes the animal's chance of survival - if you have an animal species which would behave neutral to a human-sized (or a boat-sized!) animal approaching them, and thus becomes easily slaughtered by an expedition of humans newly arrived in its territory, or hunted animals learning that humans are dangerous at distances larger than what their instinct tells them. Also, there are of course the cases of taming animals, making the behavior of that individual animal change drastically, although in the long run, you will still have instances when the animal chooses an otherwise suppressed behavior from its repertoire, that's how zoo keepers or circus trainers get injured by big animals.


Your World Will be Much More Hostile Towards Humans

Any animals that humans have been effective at killing in large numbers at some point in the past have evolved to naturaly fear us. Meaning the first time they see a human, they will typically run away or hide. This includes most species of bears, canines, felines, crocodilians, ungulates, and other primates. This is because after generations of natural selection, all living members of these species come from ancestors who thanks to genetic drift naturally avoided humans. Basically, they feel the same way about us as we feel about snakes. Any members of these species who did not naturally avoid us were more likely to end up dead for even getting close to us; so, they could not pass on their genes to their modern descendants.

To prove that genetic fear plays a big part in keeping modern humans safe, we need only look at what happens when our domestic animals (who don't fear us) start breeding with wild animals that do.

One of the most common examples used are domestic dog/wolf hybrids. Nearly all pure-bred wolves fear humans even if they have never personally seen a human. However, when a wolf breeds with a domestic dog creating wild offspring, these offspring are known to be very likely to hunt humans. Because domestic dogs do not fear us, 1/2 of their offspring can only learn to fear humans through actual experience (meaning getting hurt trying to eat one of us). This makes them far more dangerous to humans; so, they often need to be put down.

Another common issue with domestic hybrids comes in the form of wild pigs. Many breeds of wild pigs actually have a fair amount of domestic pig ancestry; so, many hunters consider them among the most dangerous of animals to hunt because they are more likely to choose to fight a human hunter instead of flee compared to other animals.

There are also some other animals such those mentioned in user2352714's answer that do not fear us; so, those animals are also good to use as behavioral models, but unlike user2352714's summation about why they do not fear us, it has more to do with evolution than individual learning. If it was just about learning, grizzly bears in remote enough of areas would feel just about as inclined to eat humans as polar bears are, but in reality they are not.

So in your world, every animal that is big enough to even consider hunting/fighting a human is likely to do so. You will also have much larger populations of dangerous predators because they've never had to compete with humans for survival before. It will take many generations and a lot of dead animals (and humans) before the animals on your planet will develop any natural fear of humans. Until then, all you have is learned fear which is much less sustainable.


Closer to C, but not quite the way you have it. There isn't such a thing as a safe/not-safe species, but predators will always look for the safest circumstances to hunt. Basically looking for lunch that is:

  • Much smaller than the predator.
  • Alone or separate from it's group.
  • Obviously weakened by injury or illness.
  • Obviously weakened by being young.
  • Hampered by the environment (e.g. a large snake might try to get away if it saw you on land, but might attack in the water).
  • Unaware that the predator is there.

One of the main differences is that large predators have been forced out (removed/killed) of many areas, which reduces how often they come into contact with humans who fit the above criteria. But if you go sideways to a world where that didn't happen, now you have grizzly bears in southern California and lions in Greece...and sending a kid out to play in the back yard alone is a bad idea.

(It's also notable what animals won't be there. In North America there won't be red foxes in the western areas or coyotes on the east coast, and no pigs or horses at all.)

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    $\begingroup$ Wolves in Canada form large packs to take down moose, which are several times larger than they are. Packs are smaller where the main prey animal is mule deer, and smaller yet when the have white tail. Coyotes don't pack other than the parents working with the current set of kids. They will take down deer with their family pack especially in heavy snowfall winters. $\endgroup$ Apr 14 '21 at 18:23

It is in the nature of animals to avoid getting hurt. This is why a swan can be "scared" away by a much smaller bird for example. If there is no reason to risk getting hurt, its better to avoid it. Remember that getting hurt is a massive problem outside of a society: infection, the energy to regenerate the wound and a lower chance to find more food or survive another encounter are all big reasons not to tempt getting hurt if you dont have to.

The template of a predator has several key factors, such as eyes that are able to focus on the same spot in front of them to judge distance. Prey like a cow for example has eyes on the sides if their heads so they can see movement much more to their sides and almost behind them. If a predator recognizes another predator it needs to make a decision: is this food or is it dangerous enough that eating it might hurt me and my chances of getting the next meal. (I'm ignoring animals that have evolved to specifically eat certain predators here). Ofcourse a predator can always decide: I think I might starve if I dont eat quickly and you look weak enough, so I'll risk it today.

There's also other animals that will happily attack humans. Hippo's are extremely territorial and wouldnt care if they've never seen you before, they'll come out and brutalize you if you dont watchout.

Honeybadgers have similarly evolved to make other creatures afraid of it. Its hyper-agressiveness helps other creatures learn to avoid it. If a human got close, it would not hesitate.

Similar for insects.

Tl, dr: yes tons of creatures would have no problems attacking humans for a number of reasons. Their only advantage is that no animals have learned to specifically target humans as prey, but predators can learn to eat them if humams "let" them.


I note that a world without humans would not necessarily be a world without people.

There are numerous species of mammals with intelligence ranges which might possibly overlapp considerably with that of humans,andwho might possibly deserve to be considered people.

I note that before the evolution of genus Homo, the supreme beings onland were members of the orber Proboscidea, elephants and their relatives. There were proposcideans on every continent escept for Antarcticaand Australia for many millions of years before humans arrived.

As late as about 13,000 thousand years ago there were over 15 species of proboscideans distributed over the world, from cold tundra to the tropics, from lush jungles to barren deserts, which are now extinct. And they may have had intelligence levels comprable to that of humans.

So humans who travel sideways in time to an alternate universe where humans never evolved might find that in every environment the dominent species is a proboscidean one.


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