The Real Biodiversity Crisis
The numbers are grim: Some 2,000 species of Pacific Island birds (about 15 percent of the world total) have gone extinct since human colonization. Roughly 20 of the 297 known mussel and clam species and 40 of about 950 fishes have perished in North America in the past century. On average, one extinction happens somewhere on earth every 20 minutes. Ecologists estimate that half of all living bird and mammal species will be gone within 200 or 300 years. Although crude and occasionally controversial, such statistics illustrate the extent of the current upheaval, which spans the globe and affects a broad array of plants and animals.
Species extinctions are, of course, perfectly natural. In the grand drama of geologic time, paleontologists have seen countless species enter and exit the stage. All species begin in some restricted setting and then spread. Most subsequently undergo differentiation, and eventually all species come to an end. The diversity of species at any point in time is simply the result of these ongoing processes, which can wax and wane in intensity. For the most part, the total number of species inhabiting the Earth probably remains fairly static.
The current losses are, however, exceptional. Rates of extinction appear now to be 100 to 1,000 times greater than background levels, qualifying the present as an era of "mass extinction." The globe has experienced similar waves of destruction just five times in the past. Devastating as they were, after each of these mass extinctions, biological diversity ultimately recovered. The time it took varied among taxonomic groups and also depended on just where the organisms lived. General recovery probably required a few million years in each case. Taking an optimistic view and assuming people will be around for a few million years yet, we wanted to explore what our descendants' world might be like.
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