It's fascinating to me - and I think we'll never see anything like this again, frankly - that from December of 1964 until about mid-1967, the Beatles were involved in a cultural/musical give-and-take that has changed music forever.
With The Beatles came out in December of '64, and had the first inclinations of influence from peers like Bob Dylan ("I'm A Loser" is the most obvious). It's not a coincidence that Dylan "went electric" following that, and while I'm not even a little bit a fan of Dylan, it's obvious that his March '65 album, "Bringing It All Back Home" was a direct result of what the Beatles were doing, and in turn IT influenced - primarily by pushing Lennon further away from the pop and skiffle of their early records - what came next: Help! and shortly thereafter, Rubber Soul. (In the meantime, you had a California band, The Byrds, who were heavily influenced by Dylan putting out their debut in mid-'65 that influenced the Beatles as well).
Rubber Soul changed the game like no one's business and from that point you had a furious back and forth between bands, each one responding and at the same time influencing the others around. It was one of the first ALBUMS, that is, a album that was a unified whole rather than a collection of songs with singles tacked on. It was a piece of art in and of itself, and following that you had Blonde On Blonde, Turn! Turn! Turn! Aftermath and Pet Sounds, then you had the Beatles taking it up a notch with Revolver, then you had Fifth Dimension, A Quick One, Good Vibrations, Between The Buttons, and Freak Out!, then the cycle rebounded and you got arguably the pinnacle of that period, Sgt. Pepper. (Dylan at this point had crashed his motorcycle, and didn't release new work until John Wesley Harding in December of '67).