Widespread species found in disturbed habitats are often expected to be human commensals. In island systems, this association predicts that dispersal will be mediated by humans. We investigated the biogeographical relationships among populations of a widespread tree skink that inhabits coastal forest and human-cultivated plantations in Southeast Asia. We sought to determine whether populations of the emerald tree skink, Lamprolepis smaragdina, dispersed via mechanisms that were not human-mediated (‘natural’ dispersal) or whether dispersal was mediated by humans. The latter scenario predicts low levels of genetic differentiation across a species' range, coupled with a genetic signature of recent range expansion.