In a post apocalyptic setting, when a virus wiped out the vast majority of our population, society is based on small settlements, barely surviving. The world is changed, nature is taking over. Lets say that 98-99% of the population is gone, and a setting is happening two generations after the "worlds end".

Taken in consideration that "old world" technology is preserved, even though the knowledge to create again is lost due to population disappearance, in my opinion, there is nothing more frightening then a group of humans anywhere with proper tools. Would like that to not be the case.

I have a problem of coming up with a type of creatures, a species, or something similar that will keep humans "in check", and in some manner make travelling, inter-settlement interactions, hunting for food, spreading across the vast land for farming etc. much more difficult. Basically a thing that is kind of preventing people from advancing from their current state of life, that they have to confine themselves in protected settlements, to keep the outside world out.


I had some thoughts of maybe evolving currently existing predators (wolves, bears, bobcats, coyotes and so on) to be bigger, meaner, smarter, but I don't think that is enough to "keep us in check". Nor it is ecologically sustainable. If a number of carnivorous predators raise, in a matter of years the number of the hunted grazing animals will fail dramatically. If rats were to evolve in the ruins of the cities - what would sustain them, what would they eat after humans have are gone and the nutrients that come with them too? Maybe introduce a whole new species?

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    $\begingroup$ this is all highly opinion based. You already have the planet apparently being sentient and making decisions. So just have your apparently sentient earth create whatever scary movie monsters you want it to. $\endgroup$
    – TCAT117
    Mar 2, 2018 at 4:50
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    $\begingroup$ Welcome to WorldBuilding Bora! Interesting question, but sadly I have to say that this is opinion-based - every answer seems to be exactly equally valid, making it impossible for the community to vote to decide which answers are good and which are bad or just mediocre. For example "Mutant humans" like in Metro seem to be a good idea - but giant killer rabbit seems equally good. I am voting to temporarily put this on hold until you edit it to correspond to our guidelines. Please take the tour and visit the help center to learn more about the site. Have fun! $\endgroup$
    – Secespitus
    Mar 2, 2018 at 8:32
  • $\begingroup$ The most obvious would be feral dog packs. They are already a problem in some urban places where the government doesn't bother controlling their numbers. They would be even more of a problem because their bite might carry infection and because they evolved (assisted by selective breeding) to look "cute" to humans, so they might judge them less dangerous than they are and get close to them on purpose. $\endgroup$ Mar 2, 2018 at 10:30
  • $\begingroup$ @Secespitus Hey mate, thank you for welcoming! Yea, my first post, so, yea, the question is kinda broad. I tried limiting the question to the evolution and sustainability of the ecological system, which should make the answers less Opinion-based... Hope thats enough. Cheers $\endgroup$
    – Bora
    Mar 2, 2018 at 15:13

2 Answers 2



Rats are cooperative, highly resilient, opportunistic eaters and pretty clever as it is. Rodents can grow to quite impressive sizes (citing both the Capybara and the now extinct East Timor Giant Rat)

The ability to organize and hunt in packs is more dangerous than actual size itself (as the fate of various megafauna at the hands of humanity may attest to) but in order to make your predators fearsome I'd let the rats grow to where one lone rat may pose a plausible threat. Say around 10-15 kilos (about the size of a large Maine Coon cat or a small Wolverine or an European Badger) for at least the largest and most dangerous individuals.

Rats are used to humans and are used to live in and around human settlements. This makes them a better threat than bears and wolves who are naturally shy. It would also make it crucial to devote a lot of time an energy just to keep rats away from your homes.

Sure, you need to handwave a bit to make the rats larger and also move them from primarily scavenging to aggressive hunters, but once you do they'll be nightmarish indeed.

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    $\begingroup$ I was going to answer the same, except I would have introduced a brain mutation rendering the rats more intelligent and dexterous. Possibly not all rats, but a few intelligent "King Rats" could easily make them a worrying menace. $\endgroup$
    – LSerni
    Mar 3, 2018 at 16:19
  • $\begingroup$ But those larger rodents are not socialized to human presence and quite elusive in the wild being largely nocturnal and solitary or small family groups. This is necessary because they require a large territory to feed larger bulk. I think of the smaller raptors in Jurassic Park and how terrifying they became once it was realized that they were cooperative in their hunting. At this point in evolution (even with sudden mutation) mankind itself is its greatest predator and the scary horror movies with mutants probably have it right. $\endgroup$
    – Hebekiah
    Jul 13, 2018 at 16:58

Humanity's greatest strength is cooperative effort (eusociality) and numbers. Without enough people and all the methods of uniting them we weren't so much the top of the food chain as just another species for a long, long time. A human's greatest hunting talent wasn't weapons or intelligence as much as the brain's growth as a redundant system with good cooling; animals stop moving when their brains get hot; humans could follow any animal until it stopped, unable even to defend itself, then hit it over the head or whatever. Fire in cooking then allowed us greater nutritional extraction from meat and vegetable sources.

So, small groups spread out around the planet could easily take a long time to advance (and already did). They themselves make good predators of themselves (did and do). There are plenty of examples like aboriginal island dwellers that didn't advance much and had limited population, where it wasn't really relevant if they were top predator or not, still just scratching for survival.

The idea of large mean predators and large dog packs would necessitate a food source and human beings don't breed and grow fast enough to sustain them reliably. So if you have it possible for large predators you make it possible for humanity to rise.

Instead, remove all the large grazing animals, everything bigger than a rabbit, and no large predators, including humans, will rise in population. This isn't so difficult as most wild populations of large herbivores have already been wiped out or reliant on domestication (abundance of food in fast growing animals, medication/disease control in genetically UNdiverse populations).

Often people who live in less densely populated areas or where cities are spread out see lots of wildlife; not just deer but elk, ducks, eagles, coyotes, etc, and think farther out in the wilderness it must be like wild animal disneyland with them packed solid; but in reality the further you go the more sparse wildlife becomes. We aren't just apex predators, we are a huge source of nutrition for very many animals (our cultivation and waste and predator control). With centralized human habitation gone (whatever catastrophe takes out all cities), wildlife will shrink and resemble the extremely sparse regular pattern as it exists far from human activity.


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