Puerto Rico's fertile soil supports one of the densest populations in the world. The Puerto Ricans are descended from Spanish colonists and also from Africans and Native Americans. Spanish and English are the official languages, although Spanish is predominant. Roman Catholicism is the main religion. Spanish is the medium of instruction, but English is studied as a second language by all students. Institutions of higher learning include the Univ. of Puerto Rico (with its main branch at Río Piedras), Inter-American Univ. at San Germán, Catholic Univ. at Ponce, and a Catholic college for women at San Juan.