A major contribution to result from the creation of the Catalogue of Endangered Languages (ELCat) is a more definitive understanding of the language families of the world and their classification. To understand the linguistic diversity of the world it is necessary to have an accurate understanding of the classification of the world's languages. Another reason that the total number of language families is uncertain has to do with the vexed question of separate languages vs. dialects of single languages. Unfortunately, sign languages are usually left out of lists of language families. In ELCat, sign languages are given under the classification heading "sign language," followed by their geographical region. The loss of any language constitutes a monumental loss of scientific information and cultural knowledge; however, the extinction of a whole family of languages is a tragedy far greater in magnitude. Each language isolate is in fact an individual language family, albeit a family of but a single member language.