Forest of fear

In 2107, due to genetic changes, a formula was discovered that prevented the occurrence of anger. Over several decades and the widespread use of this formula, corruption in societies became less and less and went towards destruction. Only a few refused to use this formula, strongly believing that using it would weaken their personal will.
Several generations have passed since the discovery of the formula. All the people were pretty much the same, and when the corruption reached its lowest point, with the spread of an epidemic, the mechanism of the formula underwent a strange transformation, and the suppressed anger of the people erupted, and everyone underwent a great transformation and took on an animal nature.
Those who refused to use this formula became the last survivors on Earth.