Humans are an ancient and technologically advanced civilization. Humanity had a long and storied history until war eventually led to their destruction, which brought the destruction of their civilization.
On Soror in the Betelgeuse system, it was discovered by three French scientists that it was inhabited by humans. The humans on Soror lived in a primitive state in the jungles, whilst being hunted by the intelligent simians. Apparently ten thousand years ago the human society on Soror was advanced in biological study, but experienced a species-wide mental regression, while the apes drastically evolved mentally.
Human civilization survived, at least in New York City, until at least the year 2500.
The humans of 3978 are shown to have devolved to a primitive state and are shown harvesting food from the trees until they are hunted by gorilla soldiers. The human children are kept as pets while adults are kept in cages.
The humans are still prisoners of the apes. When the Alpha-Omega Bomb goes off, the humans and all other life on the planet perishes when the planet is destroyed.
Travelling to 1973, Cornelius recalls from his history that a disease brought to Earth from outer space by astronauts had killed all of the world's cats and dogs. Apes became household pets to replace the pets they lost from the deadly disease and, over the course of a few centuries, became slaves.
In the year 1991, cats and dogs have already become extinct and humans put apes into slave labour due to their ability to learn and adapt, but they eventually rebelled, taking control of Ape Management and achieving their freedom.
The result of the war exterminated a large population and human cities were left destroyed by nuclear weapons which were being used in the war.
In post war society, apes and the surviving humans manage to cope in peace under the leadership of Caesar, who learns of the future destruction of Earth and attempts to change the future.
The artificial virus ALZ-113, developed by Dr. Will Rodman as an aggressive viral disease cure, instantly both increased the intelligence of ape species and killed most of the human population of the planet around the year 2016. The few surviving humans are immune to the virus.