Who sings the song in the gap commercial where Dennis hopper is sitting by a swimming pool?

YES! that song is indeed by the one and only Beach Boys, I know there's an answer, from Pet Sounds. Alternatively, Hang On To Your Ego, Brian Wilson's personal version of it. The boys didn't prefer his negative refrain with the ego dash, so they recorded I Know There's An Answer instead. On his own, Brian recorded a vocal track alone singing the different refraint, Hang On To Your Ego. It's well-haunting. enjoy it!