The doo-wop style of music influenced the Beatles early work. It was “developed by the gospel quartets of the 1940s [and] adopted by groups of young African and Italian Americans who wanted to sing somewhere other than a church and about something other than Jesus” (18). In the early chapters of John & Paul, Ian Leslie details how doo-wop inflected the Beatles’ first albums. Its “seeking, child-like quality” and “[p]assionate, joyous, and playful” sound perfectly suited the Beatles’ early musical experiments (18).

The phenomenon inspired by the Beatles’ fame and popularity became known as Beatlemania. It encapsulated the intense reaction that Beatles fans had to the bandmates, their subversive style and dress, and their disruptive cultural impact. Leslie identifies the Beatles’ performance of “She Loves You” on Sunday Night at the London Palladium as the event that “alerted the whole nation to Beatlemania” (92). Beatlemania then spread to the US (and around the world) after the Beatles’ appearance on the Ed Sullivan Show in 1963. The phenomenon is particularly defined by the raucous crowds and screaming fans that defined the Beatles’ live performances. Leslie also identifies Beatlemania as one of the primary reasons that the Beatles’ decided to stop touring in 1966.

The scientific phenomenon known as a phase shift describes a seemingly sudden change. In Chapter 7, Leslie defines a phase shift as “an abrupt transformation that has been building for some time; heated water suddenly becoming steam” (85). He then identifies several phase shifts that the Beatles underwent in their career as a group. They experienced their first notable phase shift when they secured their stint in Hamburg. Playing at the Indra and the Kaiserkeller clubs allowed them to perform the bold, experimental style they’d been cultivating in private as burgeoning musicians back in Liverpool.

Another key phase shift they underwent, Leslie argues, was the release of their first hit single “Please Please Me.” The group had slowly gained popularity and was working hard to hone their public image, but they experienced a seemingly sudden rise to global fame in the wake of “Please Please Me.” Leslie leans on this scientific terminology to capture the unprecedented nature of the Beatles’ popularity, influence, and reach.

Another scientific term, which Leslie uses to describe Lennon and McCartney’s songwriting process, is slow hunch. According to science writer Steven Johnson, a slow hunch is “an idea that takes its time to ripen and requires a lot of work to realize” (122). Leslie identifies McCartney’s experience writing “Yesterday” as one such example. While the idea for the piece came to McCartney in a dream, he didn’t pen, produce, and record the song in a rapid sweep of creative revelation. Rather, he pored over the song, allowing it to gestate over time. Leslie argues that this was in part because McCartney wasn’t sure “whether it was suitable for the Beatles,” since it was “a very long way from rock and roll” (123).

Another example Leslie offers of a slow hunch is McCartney’s song “Eleanor Rigby.” Historically (and by Leslie’s estimation) McCartney was known for his prolific songwriting capacities. As a creative team, McCartney and Lennon also worked at an uncanny speed and with marked efficiency. However, a song like “Eleanor Rigby” took McCartney “at least three months to write” (166). Like “Yesterday,” the song is an iconic Beatles’ number but it didn’t emerge with the same rapidity and ease as others of their songs.