Hip-hop turns 40 — and its parents are beaming with pride

When the Sugarhill Gang recorded “Rapper’s Delight” — the first commercially successful song to include rapping — they had no idea that it would help launch hip-hop as a global phenomenon. Forty years later, Master Gee, Grandmaster Caz and Melle Mel revisit the evolution of the movement as a hip-hop museum opens in Washington, DC.