The last chapter in the band’s Human Problems trilogy finds them stretching their dance-curious indie pop in subtly new directions. “Poor Boy” dips into the boy-girl disco of Tom Tom Club; “There Is an Everlasting Song” detours into country-folk; and “Best Friend” is about as close to the girl-group sound as you can get without a time machine. As always, the band conveys an inspiring spirit of democracy and equality, shuffling vocalists and shifting instrumentation as the song suits.