I suppose "fundamental" isn't the correct word but "hereditary" is more accurate. After Jaws and 1941 Spielberg was eyeing doing a James Bond film (in most interviews he references a "international globe-trotting film" but in the Making of Indiana Jones book its directly said that he wanted to do a James Bond film)....the powers that be wouldn't let him (probably something to do with going over budget on Jaws and 1941.) George Lucas tells Spielberg that he had something better, this was the Indiana Jones character, the idea of an adventure serial. Through story talks with Lucas, Spielberg, and Lawrence Kasdan the name "James Bond" ended up getting thrown out several times (along with Humphrey Bogart and Clint Eastwood.) This meeting really established the idea that this character was going to be Spielberg's James Bond. Before casting the idea was tossed around that they could cast multiple actors for the trilogy (assuming the first was successful), similar to James Bond...but they later rejected it because they felt it was too on-the-nose of an homage. However, they kept several aspects of James Bond in their films from the cold open in the midst of a previous adventure and the changing of love interests in each film. Indiana Jones films are James Bond films (with homages to adventure serials and Eastwood westerns) with a different skin.
I love the Indiana Jones franchise more than any other franchise...I probably know more about the character, movies, and EU material than I know about anything else. Being the massive fan that I am, given lectures on the subject, I even wrote my thesis about Hinduism and its use in Indiana Jones and the Temple of Doom, I still think Indy could be recasted, because of the franchises roots and inspiration from the James Bond series.