Many years ago, on an Earth of an alternate dimension, there lived a man named Dr. Michael Grant. Grant was a scientist who had developed an experimental chemical agent known as Cortexin. He tested his mutagenic drug on several species of animals inside of his laboratory including, apes, rats, bats and tigers. The exact purpose or nature of the Cortexin compound remains shrouded in mystery however.

Shortly after beginning the initial stages of his experiments, the world fell sway to a global catastrophe commonly referred to as the Great Disaster. Earthquakes and tidal waves erupted all across the globe and the nations of Earth found themselves at the mercy of nuclear Armageddon. Dr. Grant did not survive long enough to see his experiments come to fruition, but the lasting after-effects produced a legacy that would endure for centuries.

A large section of the Earth was rendered uninhabitable due to atmospheric nuclear radiation. However, the radiation produced a mutagenic side-effect with the surviving Cortexin-infected animals from Dr. Grant's labs. Not only were they safe from the long-term side-effects of nuclear fallout, but the strange drug permanently altered their genetic structure. With each successive generation, the various animal species began to evolve adopting specific physical human characteristics. Within two human generations, apes, birds, felines, canines and many other breeds were developing heightened intellect, bipedal locomotion, extra fingers, toes, thumbs and even the ability to articulate.

As each race grew in strength and numbers, they began to form primitive tribal societies and family clans. Many of the clans did not live in harmony with their cousins, and a culture of survival of the fittest soon developed among them.