The so called "Mexican trinity" is mentioned a number of places in the book. The first mention is in Chapter 6, on p. 109 in the paperback edition. The Mexican trinity consists of three crops that tended to be grown together by Indians in Mexico. These crops grew well together and helped one another to thrive. The three crops were corn, squash, and beans. Diamond also mentions this trinity in Chapter 8, page 150 and 151. There, he says that Native Americans in what is now the Eastern US were not really able to farm effectively until the Mexican trinity arrived in their area.