One story of the Grey's always fascinated me.

There was a theory they are future versions of us. Geoengineered the planet, or ship and sent biomechanical androids.

They messed up their genes, or their controllers. They're sent here to get code from the past to fix their race.

Lots of holes and don't really believe it.

Truth is stranger.

A genetic collapse has already occurred. The very forced integrations called for destory biodiversity. However, we are at a point where it is reclaimable by non-genetic sequencing means. That can change with many things on the horizon. Like nuclear war.