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4 Introduction will probably not go down in the history books together, there is a common thread that marks them as significant steps forward in our collective understanding of ourselves and the earth. Both events forced us to consider ourselves from a new vantage point. Those first NASA photographs of our tiny planet suspended in the blackness of space confronted, us with a planetary perspec- tive of our size and fragility in the cosmos. The Endangered Spe- cies Act confronts us with an ecological perspective of ourselves in the biosphere. As Senator Patrick Leahy stated during the de- bate over the 1978 amendments to the act: "Ultimately, we are the endangered species. Homo sapiens are perceived to stand at the top of the pyramid of life, but the pinnacle is a precarious station. We need a large measure of self-consciousness to con- stantly remind us of the commanding role which we enjoy only at the favor of the web of life that sustains us, that forms a foundation of our total environment. We share the planetary gene pool with that snail darter in the Little Tennessee River."Z The more we learn about the earth's natural history, the more we have come to realize that we are in the midst of an extinction episode of historic proportion. There have been other extinction episodes in the history of life on earth.3 At the end of the Cre- taceous period, a large number of marine and terrestrial species disappear from the fossil record. Among them are the dinosaurs. Apparently all evolutionary lineages of the dinosaurs went ex- tinct approximately 65 million years ago. Further back in geo- logical time, the fossil record shows an even more devastating extinction spasm during the late Permian (250 million years ago). During that time, the fossil record suggests that as many as 52 percent of all existing families of marine animals were lost. Between these "mass extinction episodes," it appears there were also a number of smaller extinction events that scientists often use to mark the epochs and periods of geological time. Overall, it is estimated that the current stock of species represents between 2 and 10 percent of all species that have ever lived on earth 4 In other words, extinction is a biological reality. What sets the current extinction episode apart from the others, however, is that it is largely being caused at the hands of a single species. Moreover, the current rates of species loss appear to be unprece- dented. Evidence in the fossil record suggests that historical extinction rates are trivial compared to those of the past several