Nas and Marley (one of Bob’s sons) first hooked up a few years ago for a track on Marley’s Welcome to Jamrock album. For Distant Relatives’ 13 songs, they present a sort of history lesson, tracing hip-hop to Africa and charting its long, varied course through the years. The mix — not so surprisingly — is somewhere between Marley’s Jamaican reggae and Nas’s NYC hip-hop. Opener “As We Enter” flips through both artists’ backgrounds for inspiration, with a swinging beat and twisty rhymes finding a common ground. But elsewhere the results are more strained, as Nas and Marley step out of each other’s way during verses (mostly Nas) and choruses (mostly Marley). Lil Wayne and K’Naan are also here, but they’re lost in the shuffle, as is Distant Relatives’ original concept. A few songs play along with the African-roots setting — like the biting “Strong Will Continue” — but the album ends up somewhere else altogether.