The Fifth World


The former domesticated cat has rewilded itself to become an exceedingly successful mesopredator all over the world. Cats partially domesticated themselves following the invention of agriculture, drawn by the mice attracted by stored grain. Though cats and humans maintained a friendship over ten thousand years, cats always remained at least somewhat independent. With civilization’s collapse, people began living less settled lives and stopped storing as much food that would attract rodents, thus ending the conditions that originally drew humans and cats together.

Habitat and behavior

Cats live on every continent, including Antarctica. Most cats live in small, temporary colonies, mostly consisting of a few related female cats and their kittens. Male cats tend to roam over large areas and live solitary lives, except for occasional breeding.

Most cats in the Fifth World have become fully feral and avoid humans, but occasionally humans might find a kitten whose mother has died and raise it as a pet. These cats never develop the usual fear of humans and sometimes remain with their human friends for the rest of their lives. Normally this only goes for female cats, as intact male cats will generally become aggressive in adulthood and leave their human families. Some cats that stay with humans will end up forming colonies near the human village.

Ecological impact

Cats hunt with remarkable efficiency. As humans carried them around the world, they contributed to mass extinction, devastating local songbird populations. Following collapse, former housecats found their way outside and survived by hunting even more. Across North America, where many ancient families kept them as pets and civilization had largely wiped out apex predators, they drove many once-dominant mesopredators to extinction, including raccoons, skunks, and foxes. However, once apex predators such as coywolves and panthers returned, they preyed on cats enough to keep their numbers in check. That delicate balance continues to this day.


Before collapse, scientists genetically engineered a breed of cat whose fur would change green in the presence of dangerous levels of radiation. These genes spread rapidly among the feral cat population in the years following collapse. Now most cats contain at least some traces of these genes. Stories and songs warning of green cats abound. The glimpse of a green cat in the forest is a signal of doom in many traditional stories.