Most of the observable causes of decline in biodiversity, according to ecologists, stem either directly or indirectly from human activities. These include hunting (which is believed to have caused the extinction of many species since prehistoric times), introducing non-native or alien species to new environments, and converting former wildlife habitat into farms or urban areas. Homo sapiens’ impact on the world’s biodiversity is a direct result of its success in colonizing much of the planet’s area and appropriating its natural resources. “Human beings have become a hundred times more numerous than any other large land animal in the history of life,” asserts biologist Edward O. Wilson. Humanity’s success in exploiting and changing the natural environment, Wilson argues, invariably results in “reducing many other species to rarity or extinction.”

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