Only two people on Earth are known to speak the Ayapanec language, Manuel Segovia and Isidro Velasquez, old men of few words who are somewhat indifferent to each other's company.

When Segovia and Velasquez pass away, their language also will go to the grave. It will mark the demise of a unique way of describing the lush landscape of southern Mexico and thinking about the world.

Ayapanec isn't alone in its vulnerability. Some linguists say that languages are disappearing at the rate of two a month. Half of the world's remaining 7,000 or so languages may be gone by the end of this century, pushed into disuse by English, Spanish and other dominating languages.

The die-off has parallels to the extinction of animals. The death of a language, linguists say, robs humanity of ideas, belief systems and knowledge of the natural world. Languages are repositories of human experience that have evolved over centuries, even millennia.

"Languages are definitely more endangered than species and are going extinct at a faster rate," said K. David Harrison, a linguist at Swarthmore College in Pennsylvania and the author of the book "When Languages Die." "There are many hundreds of languages that have fewer than 50 speakers."