For this study, we used mitochondrial DNA (mtDNA) sequences to infer the relationships among the different taxa of spider monkeys we sampled. Mitochondrial DNA has been suggested as an ideal marker to conduct studies of species and subspecies relation ships as this marker (1) displays extensive intraspecific polymorphism, (2) typically evolves faster than nuclear DNA, and (3) is present at higher copy number and thus is more readily extracted and amplified from a variety of sample types (feces, hair) than is nuclear DNA (Avise, 2000).