For those interested in the nitty gritty.......

The Genre.....Barbershop harmony is a style of unaccompanied vocal music characterised by consonant four-part chords for every melody note.  The melody is consistently sung by the lead (mostly!), with the tenor harmonising above the melody, the bass singing the lowest harmonising notes and the baritone completing the chord.  The melody is not sung by the tenor except for an infrequent note or two, in tags or codas, or when some appropriate embellishing effect can be created.  Occasional brief passages may be sung by fewer than four voice parts.

Brief history...  Barbershop started in the USA at the time of prohibition when men used to find entertainment singing together in quartets.  The society for the preservation of barbershop singing in the USA (SPEBSQSA) is responsible for much of the revival of the genre taking it into schools and colleges and having a regular injection of young people leaving college and joining barbershop choruses.  The ladies decided that they could do just as good a job at harmony and finding themselves left at home they formed an association in America just for women!