For spider monkeys, several of these hypotheses have been proffered as possible explanations for diversification and specia- tion. For example, Froehlich et al. (1991) suggested that a combination of the river barrier and refugia hypotheses might explain patterns of speciation in spider monkeys, while Medeiros et al. (1997) suggested that the contraction and expansion of tropical forest refugia during the Pleistocene is the most plausible scenario for explaining spider monkey diversity generally and the origins of A. paniscus in particular.