"How Deep is Your Love" by the Bee Gees was No. 1 on the Billboard pop chart 40 years ago.
It was the first single from the soundtrack to the film "Saturday Night Fever," one of the best-selling soundtracks of all time.
The Bee Gees were hired to write songs for the movie after all the scenes were shot. They wrote this song thinking that it would be sung by Yvonne Elliman, but the producers insisted that they record it instead.