New research on lizards in the Caribbean demonstrates that species diversification is limited by the environment. The finding supports and extends the MacArthur-Wilson theory of island biogeography. It’s long been accepted by biologists that environmental factors cause the diversity — or number — of species to increase before eventually leveling off. Some recent work, however, has suggested that species diversity continues instead of entering into a state of equilibrium. But new research on lizards in the Caribbean not only supports the original theory that finite space, limited food supplies, and competition for resources all work together to achieve equilibrium; it builds on the theory by extending it over a much longer timespan.