Hanging on: Pandas have become the endearing symbol of the environmental challenges the Earth faces. Only about 1,600 of the cuddly creatures remain in the wild. Humans' encroachment on the fragile habitats of many species threatens biodiversity. Last year, 16,928 threatened species were on the World Conservation Union's Red List, up from 11,046 in 2000. Above, a panda cub climbs at China's Giant Panda Protection and Research Centre on June 28, 2006, in Wolong Nature Reserve.

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