In No Turning Back: The Life and Death of Animal Species (HarperCollins, $25.95), Richard Ellis dwells on our ignorance of how extinctions occur -- apart, that is, from those we humans have caused ourselves, whose number is legion. "We know precisely why there are no more giant sea cows, passenger pigeons, Tasmanian tigers, and Carolina parakeets," Ellis writes, "and why there may soon be no more California condors, giant pandas, black rhinos, Galapagos tortoises, or Chinese river dolphins. We destroyed their habitat so they had no place to live, or we killed them, every last one. With this obvious exception, there is no inclusive theory as to why extinction happens."

In a book otherwise low on cheer, Ellis devotes a chapter to "the anti-extinctions": discoveries of animals previously not known to exist. One of these occurred as recently as the mid-1990s and involved a creature you might think it would be hard to miss: the wild Bactrian camel. The Bactrian camel (the very species that appears in the recent movie "The Story of the Weeping Camel") was thought to survive only in domesticated populations, but about a decade ago an expedition headed by a noted camelphiliac, John Hare, found that not only were there wild Bactrians in China's Xinjiang province (in a region that had been off-limits as a nuclear-test site for decades) but also that "because there was no fresh water available" this genetically separate population "had developed the ability to drink salt water." In 1999, Ellis notes, China set aside the Arjin Shan Lop Nur Nature Reserve to protect the Bactrian camel and other local species.

-- Dennis Drabelle

The extinct dodo bird and the surviving wild Bactrian camel