Why should the disappearance of beetles, plants, or birds concern us? First, a species, the irreplaceable product of millions of years of development, is of intrinsic value. Another, perhaps more compelling, reason to conserve biological diversity is pure self-interest. Like every species, ours is intimately dependent on others for its well-being. Time after time, creatures, even those once thought useless or harmful, are found to play crucial roles in natural systems. Predators driven to extinction no longer keep populations of potential pests in check; earthworms or termites killed by pesticides no longer aerate soils; mangroves cut for firewood no longer protect coastlines from the erosive force of the sea. The above argument as a whole seeks to establish that ['there are no species in nature that are, properly considered, harmful to people', 'it is only selfish people who wish to conserve biological diversity', 'whether species to which people pay little attention become extinct is not of great importance except to scientists', 'species of plant and animal life should be preserved because they are valuable both in themselves and for the well-being of people']