PETÉN, GUATEMALA—Phys.org reports that a team of researchers led by Gloria Hernandez of the University of Mérida measured stable carbon and nitrogen isotopes in the bone collagen of 57 people, and carbon isotopes in the tooth enamel of 37 people, who lived in small communities in northern Guatemala during the Maya Classic period (A.D. 250–950). The scientists then compared their results with published data obtained from human remains dated to th…