THE CHALLENGE OF EXTINCTION

The causes of extinction, the importance of genetic diversity, and efforts to alter conditions that threaten nearly 20% of all species on earth in the next 20 to 30 years. While the examples mentioned here are intriguing, the organization of this entry in the ``Environmental Issues'' series is confusing. Under ``Diversity,'' Patent discusses the causes of extinction—habitat destruction, killing for profit, pollution—and then goes on to discuss keynote species, corn that never dies, improving tomatoes, and domesticating the kouprey (a kind of wild ox). Statements like this one lack sources: ``One of the best examples of why it is to the advantage of humans to keep wild species from disappearing is the discovery of teosinte...its value to agriculture is estimated at $6.82 billion annually!'' A disappointment from this usually reliable author. Photos and drawings not seen. Glossary; further reading; places to write for information; index. (Nonfiction. 12-14)