land and other natural resources build, the intensity of natural disasters—especially flood and drought—can become aggravated, and the effects more tragic.

There are other, more immediate causes of resource degradation in developing nations, including continuing military conflicts, misguided or misapplied policies that discourage conservation and, above all, persistent and crushing poverty—all of which leave people with few choices in managing land and natural resources. In the past, world leaders in both the developing and the developed nations have tried to address these essentially interrelated problems as separate phenomena. Other global concerns, such as climate change resulting from the buildup of greenhouse gases in the atmosphere, were regarded as separate issues—if they were regarded at all. Few recognized the fundamental need to consider environmental effects and prevent environmental degradation at all stages of development.

Times appear to be changing. The level of concern among world leaders, including the international development agencies, has risen. Many are rethinking their priorities with respect to the allocation of resources to slow the degradation. Whether it is too late for leaders and development agencies to have a beneficial effect depends on what is done and how quickly. Furthermore, this new awareness comes at a time when dramatic political changes in the Soviet Union, Eastern Europe, Central America, the Middle East, and Africa are creating a competing demand for development resources. There are no easy choices, but there can be no turning back to the time when the short-term enrichment of human societies entailed the long-term impoverishment of the living world on which all societies depend.

BIODIVERSITY: DEFINITIONS AND VALUES

The diminishing of the Earth's biological diversity has consequences far more profound than other, sometimes more widely recognized, environmental dilemmas. Because the loss of biodiversity is irreversible—species that are lost are lost forever—the potential impact on the human condition, on the fabric of the Earth's living systems, and on the process of evolution is immense. Our species has evolved biologically and culturally in a highly diverse world. Our past interactions with other life forms have shaped our humanity in intricate ways, and our future cannot be separated from that of the other life forms with which we share the planet.

Biological diversity refers to the variety of life forms, the genetic diversity they contain, and the assemblages they form. Biological systems, whether tundra, forests, savannahs, grasslands, deserts, lakes, rivers, wetlands, coastal communities, or marine ecosystems,



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