Final answer:
The Beatles adopted a new work regimen to create more serious songs, mirroring the musical evolution of the 1960s that pushed the boundaries of rock 'n' roll and reflected changing youth culture.
Step-by-step explanation:
The Beatles' transition to composing more serious songs reflected the broader cultural shifts occurring during the 1960s, including a push for deeper artistic expression and rebellion against conventional norms. Unlike the slaves who composed songs filled with both joy and sadness without concern for time or tune, and in contrast to the Beat generation that expressed themselves through literature, The Beatles channeled their creativity into music which soon became emblematic of suburban youth culture.
Their later songs in the 1960s showcased maturity, as they too, like other artists of the era from Motown and beyond, were pushing the boundaries of rock 'n' roll. This evolution can be seen as part of the commercialization and transformation that reshaped the music landscape, where new, more complex themes in music began to replace the escapism of earlier decades.