Hijack

One pitch a day: in August of 2011, I dedicate twenty minutes each day to writing an « elevator pitch » for a story or a game.

In prehistoric times, an alien civilization nudges humankind forward on the evolutionary path, then retreats to other regions of space to enjoy different flavors of life. Events unfold mechanically from then on. Once human technology reaches the adequate level, the master plan of the godfather race comes to fruition. It happens in a laboratory. Some of the scientists who research cures to diseases stumble upon the vaults of possibilities hidden into human genes. They unlock them and soon after devise efficient treatments.
The secondary effect, which behaves like an airborne virus, does not kick in before many months, and by then containment is not an option anymore. The human race undergoes a genetic reconfiguration on a global scale.
All the babies who get born after the scientists unleash what was hidden in the genetic vaults are not human babies. They are alien babies with alien bodies, waiting to host alien minds.
Alien machines detect these changes and alert the alien race, which sends millions of minds to Earth. These reincarnating hedonists are perfectly happy to enjoy the civilization humans built. They inherit the planet, its art, its cultures and its history. They begin to enjoy this flavor of life with the assistance of their aging parents.
Some humans object to the genocide perpetrated by their babies.