Biocultural diversity is defined by Luisa Maffi as "the diversity of life in all its manifestations: biological, cultural, and linguistic — which are interrelated (and possibly coevolved) within a complex socio-ecological adaptive system." "The diversity of life is made up not only of the diversity of plants and animal species, habitats and ecosystems found on the planet, but also of the diversity of human cultures and languages." Certain geographic areas have been positively correlated with high levels of biocultural diversity, including those of low latitudes, higher rainfalls, higher temperatures, coastlines, and high altitudes. A negative correlation is found with areas of high latitudes, plains, and drier climates. Positive correlations can also be found between biological diversity and linguistic diversity, illustrated in the overlap between the distribution of plant diverse and language diverse zones. Social factors, such as modes of subsistence, have also been found to affect biocultural diversity.
Cultural traditions are passed down through language, making language an important factor in the existence of biocultural diversity. There has been a decline in the number of languages globally. The Linguistic Diversity Index has recorded that between 1970 and 2005, the number of languages spoken globally has decreased by 20%. This decline has been especially observed in indigenous languages, with a 60% decline in the Americas, 30% in the Pacific, and 20% in Africa. Currently, there are 7,000 languages being spoken in the world. Half the population speaks only 25 of these languages, the top 5 in order being Mandarin, Spanish, English, Hindi, and Bengali. The remaining 6975 languages are divided between the other half of the population. Because languages develop in a given community of speakers as that society adapts to its environment, languages reflect and express the biodiversity of that area. In areas of high biodiversity, language diversity is also higher, suggesting that a greater diversity in culture can be found in these areas. In fact, many of the areas of the world inhabited by smaller, isolated communities are also home to large numbers of endemic plant and animal species. As these people are often considered to be "stewards" of their environments, loss of language diversity means a disappearance of traditional ecological knowledge (TEK), an important factor in the conservation of biodiversity.