The decline of Africa's largest mammals
The human species is causing profound climatic, environmental, and biotic disruptions on a global scale. In the present time (now called the Anthropocene), most species of large terrestrial herbivores are threatened with extinction as their populations decline and their geographic ranges collapse under the pressure of human hunting, poaching, and encroachment (1). Although the scale of ongoing anthropogenic ecological disruptions is unprecedented, human-driven extinctions are not new: There is strong evidence that humans played a major role in the wave of megafaunal losses at the end of the Pleistocene, between about 10,000 and 50,000 years ago (2). But when did humans, or our ancestors, begin to have such a profound effect on large herbivores to the point of causing extinctions? On page 938 of this issue, Faith et al. (3) provide evidence to help answer this question. They track the number of megaherbivore species (mammals weighing more than 1000 kg) in eastern Africa from the late Miocene, about 7 million years ago, to the present. Their analysis indicates that megaherbivore diversity began to decline in the early Pliocene, about 4.6 million years ago.