Cause of the apocalypse: In 2050, the human gene editing technology "Project Dawn" went out of control, causing a synthetic enzyme called "Pryon Particle" to spread in the global atmosphere. It is not fatal, but it catalyzes an irreversible "reverse evolution" in organisms.
Variation settings:
Human beings: 90% of the population undergoes "explicit evolution", that is, atavism. Some people reverted to their ancestors as apes, losing the ability to speak, and their muscles became gnarled; some people reverted to their ancestors as more ancient reptilian brains, and became living corpses that only knew how to eat and bite. They are collectively known as the "old people".
Survivors: 10% of humanity remain unchanged and are called "new people". They do not have any superpowers. Their only advantage is that they still maintain the thinking, logic and emotions of modern people.
Reconstruction of the biological chain: Domestic animals revert to beasts (pet dogs regain their wolf nature and become larger), insects become giant, and plants become more primitive and aggressive. Humans are no longer at the top of the food chain, just one of the prey.
The core contradiction: the extreme lack of survival resources, and the natural aggression of the "old people" against the "new people". What's more important is the internal struggle among the survivors over "whether to use old people for experiments" and "whether to abandon the old, weak, sick and disabled".
