Wasteland was more than a "spiritual ancestor" to Fallout.
The original project that Interplay started was going to be Wasteland 2, only at the last minute EA refused to let Fargo use the Wasteland title.
Interplay then renamed it Fallout: A GURPS Post-Nuclear Adventure, and were going to use the Steve Jackson RPG system (thanks mostly to Tim Cain's love for the GURPS game system and Fargo's desire for a known product).
After a very rocky relationship between the development team and Steve Jackson Games, Interplay decided to drop both Steve Jackson and GURPS from the title.
The project finally became known as Fallout.