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.
Cornelius says that a disease brought to Earth from outer space by one of the astronauts killed all of the world's cats and dogs, leaving humans. Apes became household pets to replace the pets they lost from the deadly disease, over the course of a few centuries.
Human civilization survived, at least in New York, until at least the year 2500.
In the year 1991, 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 Earth's 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.
The humans are shown to be primitive and were shown harvesting food from the trees until they are hunted by the gorilla soldiers. The human children were kept as pets while the adults were kept in cages.
The humans are still prisoners of the apes. When the Alpha-Omega Bomb went off, the surviving humans and other life on the planet perished when the planet was destroyed.
The artificial virus ALZ-113, developed by Dr. Will Rodman as a 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.
More to come...