地球史好似一场演出，将各类生物比作舞台上的演员，它们依次登台，演绎了一场精彩而隆重的晚会。但是，有人登场，就会有人退场。

Human impacts

　　According to a report by the Center for Biodiversity and Conservation (1999), there is a general pattern that has emerged related to human activity in the past 50,000 years. After the emergence of modern humans, few known extinctions occur in those areas of longest human occupancy (Africa and Eurasia), and those that occur are spread out. But the migration of human beings into other areas is linked to the loss of many large vertebrate species.

　　For example, about 50,000 years ago, Indonesia lost about 50 percent of its large mammals when human beings migrated there, and the movement of human beings into Australia 60,000 to 40,000 years ago resulted in large mammals and other vertebrates disappearing. In North and South America, there was a loss of some 135 mammal species, including 70 percent of North America's large mammals, between 12,500 and 10,000 years ago, when humans migrated from Asia. The settlement of Madagascar (2,000 years ago), the West Indies (7,000 years ago), islands of the Mediterranean Sea (10,000 years ago), Hawaii (1,600 to 1,400 years ago), and New Zealand (1,200 to 800 years ago) all coincided with extinction episodes. Notably, all terrestrial vertebrates outside of Africa and Asia that weighed more than 1,000 kilograms have become extinct.

　　Among the human activities currently considered as impacting extinctions are overhunting (either directly, or indirectly by decimation of prey populations), introduction of infectious diseases (perhaps carried by associated animals such as rats or birds), increased interspecific competition, habitat destruction, and the introduction of exotic species. The destruction of large mammals could have had even wider impacts on the ecosystems of which they were part.

　　Many biologists believe that we are at this moment at the beginning of an accelerated anthropogenic mass extinction. Eldredge has stated "It is…well established that the earth is currently undergoing yet another mass extinction event…and is clear that the major agent for this current event is Homo sapiens” (Eldredge 1999). E.O. Wilson of Harvard, in The Future of Life (2002), estimates that at current rates of human destruction of the biosphere, one-half of all species will be extinct in 100 years.

　　Those who are skeptical about the current mass extinction argue that even if the current rate of extinction is comparable or higher than the rate during a great mass extinction event, as long as the current rate does not last more than a few thousand years, the overall effect will be small. There is still hope, argue some, that humanity can eventually slow the rate of extinction through proper ecological management. Current socio-political trends, others argue, indicate that this idea is overly optimistic. Many hopes are set on sustainable development.

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