Mellowship starts in E major for the intro, then goes into a funky B major bass line in the verse. They probably wrote the song around the verse bass and guitar, so that's where it got the name. Then it goes into an E minor chorus (good god etc.) then back into the verse. After the next chorus it goes into an B minor modulating to A minor guitar solo. Then back into the B major verse and finally back into the E major intro. Contrary to what Tabs says, Flea does not fully show off his popping and slapping skills. He just plays very funky and close to the bridge, with a lot of treble, which can sound a bit like slap.