The role of the bass in a band, in music in general, is crucial. The bass part is similar to a planet - in that it exerts a gravitational pull on the other parts, which can perhaps leap or even occasionally fly, but not escape. In fact, one of the elements that gives music its powerful emotional force is the gravitational or magnetic attraction between the bass and the rest of the instrumentation. Therefore, it is not a surprise that, like Motown with James Jamerson, the best player in the Beatles was the bassist. Ringo Starr once called Paul McCartney the most melodic of bass players, which is succinct and true; his playing always has a singing quality (cf. Duke Ellington who used to ask his band, after they had played something new, if everyone liked their parts). It was an irreplaceable element of the Beatles' music, in whatever style they explored. The two most notable tracks on Starr's recent release, Y Not (2010), both feature McCartney: one as a singer and the other as a bassist. On the former, "Walk with You", it is interesting to hear him in a duet with Ringo. The Beatles rarely used this device, in the sense where more than one singer can be clearly identified as singing from their own personality. Usually, there was a lead vocal performance with the identity of the singer easy to hear, and the others providing backing with the singers much harder to pinpoint. It was amazing, and I don't know how they did it. But on this track, it's clearly Ringo and Paul singing together (http://www.youtube.com/watch?v=c68v6WIZeRI). The other track is called "Peace Dream", and it's a wonderful treat to hear the great rhythm section together again. Also, check out the very cool references to Lennon and Harrison, via both lyrical and guitar allusions: http://www.youtube.com/watch?v=UE7ju4lU2W0