Of the estimated 7,000 languages spoken in the world today, linguists say, nearly half are in danger of extinction and likely to disappear in this century. In fact, one falls out of use about every two weeks.

Some languages vanish in an instant, at the death of the sole surviving speaker. Others are lost gradually in bilingual cultures, as indigenous tongues are overwhelmed by the dominant language at school, in the marketplace and on television.

New research, reported yesterday, has found the five regions where languages are disappearing most rapidly: northern Australia, central South America, North America’s upper Pacific coastal zone, eastern Siberia, and Oklahoma and the southwestern United States. All have indigenous people speaking diverse languages, in falling numbers.

The study was based on field research and data analysis supported by the National Geographic Society and the Living Tongues Institute for Endangered Languages. The findings are described in the October issue of National Geographic and at languagehotspots.org.