One of Jocano's earliest major contributions to the field of cultural anthropology and a significant contribution to recorded Filipino folk literature was the documentation of the epic poem
Hinilawod (which means "Tales From The Mouth of The Halawod River"). The epic recounts the story of the exploits of three Sulodnon demigod brothers, Labaw Donggon, Humadapnon and Dumalapdap of ancient Panay. Jocano, assisted by a radio technician from the Central Philippine University, convinced Sulod folk chanters Ulang Udig and Hugan-an to recount the story, and allow them to record it on cassette. The process of acquiring this permission took years, from Jocano's first contact with Ulang Udig in 1955 to the recording of Hugan-an's 30-hour performance of the epic in 1957. Jocano eventually also published the text in his book "
Hinilawod: Adventures of Humadapnon Tarangban I" (The epic was once again recorded in 1999, by researcher Alejo Zata, working among Sulod natives who still performed it and for whom the epic was still very much an active part of their culture.) == Core Population Theory==