Final answer:
While Jared Diamond's specific reference to the Rapanui's primary meat source isn't provided in the information, it is known they consumed lean meats as part of a diverse diet, making up about 20% of their intake.
Step-by-step explanation:
The most common meat source for the Rapanui (the people of Rapa Nui) before the 1600s, according to Jared Diamond, was not specified in the information provided. However, it is generally recognized that the Rapanui's diet included a variety of foods of plant origin and a certain amount of cooked lean meat, which made up roughly 20 percent of the diet by weight. This meat came from animals naturally living on the island, likely sea birds and other small land animals, as the deforestation of the island would have made larger game scarce and the lack of wood for boats restricted deep-sea fishing.