To know pop-music genealogy, thoroughly, you can’t just listen. Strain to hear – you’ll pick out the violins – the wood sound of pop’s great-great-great-grandfather: 17th-century German composer and one-hit wonder Johann Pachelbel. Pachelbel wrote The Canon and Gigue in D major, possibly as a gift for a friend’s wedding. The Canon in D, as it’s known today, trots out a chord progression that musicians have loved, adopted, groomed often and sundry – and all centuries after Pachelbel’s death, of course (in the 1990s especially). Here, Vampire Weekend inherits the progression in 2013’s “Step.” Unlike other surrogates (unlike ‘93 Pet Shop Boys in “Go West”), VW recalls the wedding context – a held-in sigh. Still, Pachelbel lives here in odd company, as songwriter Ezra Koenig also borrowed lyrically/melodically from ‘90s rap group Souls of Mischief, who borrowed melodically from ‘70s jazzist Grover Washington, Jr. In his own context, Koenig turns over expectant youth, and not without pain.