Human hunting and climate change are two competing hypotheses for the extinction of many large-bodied mammals at the terminal Pleistocene. However, the information used to characterize the body sizes of these animals has been qualitative and no investigation has been made into the body size distributions of all extant species prior to the extinction. We compiled detailed data on body sizes of all extant mammals during the late Pleistocene of North America, South America, Africa and Australia. Because of the difference in timing of the extinction events, the examined biotas for the New World and Africa are approximately 12,000 to 15,000 years old whereas the Australian biota is approximately 50,000 years old. Body size distributions of all mammals in North America, South America, Africa and Australia before and after the late Pleistocene show a similar large-size selectivity of extinctions across continents, despite differences in timing. All extinctions coincide with the colonization of the continent by aboriginal man, but do not necessarily coincide with climate change. Not surprisingly this pattern was recapitulated at the ordinal level. Further, historical (within the last 300 years) extinctions in Australia demonstrate a higher susceptibility of small and medium sized mammals. We conclude that the late Pleistocene extinctions were caused primarily by human hunting, whereas historical extinctions were due mostly to habitat alteration and exotic species introduction.