Language extinction triggers the loss of unique medicinal knowledge Rodrigo Camara-Leret´ a,1 and Jordi Bascomptea aDepartment of Evolutionary Biology and Environmental Studies, University of Zurich, CH-8057 Zurich, Switzerland Edited by B. L. Turner, Arizona State University, Tempe, AZ, and approved May 9, 2021 (received for review February 24, 2021) Over 30% of the 7,400 languages in the world will no longer be cited by only one language, respectively (Fig. 2). The fraction spoken by the end of the century. So far, however, our under- of unique knowledge that is explained by cultural turnover (i.e., standing of whether language extinction may result in the loss languages having different knowledge of the same species), as of linguistically unique knowledge remains limited. Here, we ask opposed to species turnover (i.e., each language using differ- to what degree indigenous knowledge of medicinal plants is ent plant species), is 56%, 18%, and 50% in North America, associated with individual languages and quantify how much northwest Amazonia, and New Guinea, respectively. Our find- indigenous knowledge may vanish as languages and plants go ing of a strong pattern of unique knowledge raises the question extinct. Focusing on three regions that have a high biocul- of whether unique knowledge is mostly found in languages that tural diversity, we show that over 75% of all 12,495 medicinal are threatened. plant services are linguistically unique—i.e., only known to one Our analysis indicates that threatened languages support 86% language. Whereas most plant species associated with linguis- and 100% of all unique knowledge in North America and tically unique knowledge are not threatened, most languages northwest Amazonia, respectively. This result highlights that that report linguistically unique knowledge are. Our finding of the Americas are an indigenous knowledge hotspot (i.e., most high uniqueness in indigenous knowledge and strong coupling medicinal knowledge is linked to threatened languages) and, with threatened languages suggests that language loss will be thus, a key priority area for future documentation efforts. By even more critical to the extinction of medicinal knowledge than contrast, threatened languages account for 31% of all unique biodiversity loss. knowledge in New Guinea. However, in the absence of an island- wide linguistic survey, the true status of New Guinea’s languages ECOLOGY indigenous languages j ecosystem services j biocultural diversity is difficult to assess. A recent study in Papua New Guinea showed that only 58% of 6,190 students, compared to 91% of their parents, are fluent in indigenous languages (14). Crucially, ndigenous people have accumulated a sophisticated knowl- the varied medicinal plant uses known to students fluent in Iedge about plants and their services—including knowledge indigenous languages are replaced by a few uses mostly con- that confers significant health benefits (1)—that is encoded in centrated in nonnative plant species in the students who do not their languages (2). Indigenous knowledge, however, is increas- speak indigenous languages. Such a dramatic decline in language ingly threatened by language loss (3) and species extinctions skills in a single generation suggests that our language-threat SUSTAINABILITY SCIENCE (4, 5). On one hand, language disuse is strongly associated data from Glottolog (15) likely underestimate the percentage with decreases in indigenous knowledge about plants (6). On of unique knowledge associated with threatened languages in the other hand, global change will constrain the geographic New Guinea. ranges of many human-utilized endemic plants and crops (7, 8). Together, language extinction and reductions in useful plant species within the coming century may limit the full poten- Significance tial of nature’s contributions to people and the discovery of unanticipated uses. So far, however, our understanding of the The United Nations proclamation of 2022–2032 as the Interna- degree to which the loss of indigenous languages may result tional Decade of Indigenous Languages aims to raise global in the loss of linguistically unique knowledge and how this awareness about their endangerment and importance for risk compares to that posed by ecological extinction has been sustainable development. Indigenous languages contain the limited (Fig. 1). knowledge that communities have about their surrounding Unraveling the structure of indigenous knowledge about plants and the services they provide. The use of plants in medicinal services has important implications for its resilience medicine is a particularly relevant example of such ecosys- (9). Most indigenous cultures transmit knowledge orally (10). tem services. Here, we find that most medicinal knowledge Therefore, if knowledge about medicines is shared widely among is linguistically unique—i.e., known by a single language— indigenous groups that speak different languages, knowledge and more strongly associated with threatened languages than resilience would be high. That is, even if some indigenous lan- with threatened plants. Each indigenous language is there- guages go extinct, their medicinal plant knowledge would still be fore a unique reservoir of medicinal knowledge—a Rosetta safeguarded in other surviving languages with whom such knowl- stone for unraveling and conserving nature’s contributions to edge is shared. To assess the extent of this, we analyzed three people. large ethnobotanical datasets for North America (11), north- west Amazonia (12), and New Guinea (13). Together, these data Author contributions: R.C.-L. and J.B. designed research; R.C.-L. performed research; span 3,597 medicinal plant species and 12,495 plant services asso- R.C.-L. analyzed data; and R.C.-L. and J.B. wrote the paper.y ciated with 236 indigenous languages (Materials and Methods). The authors declare no competing interest.y We defined a “medicinal plant service” as the combination of a This article is a PNAS Direct Submission.y plant species and a medicinal subcategory (e.g., Ficus insipida + This open access article is distributed under Creative Commons Attribution-NonCommercial- Digestive System). NoDerivatives License 4.0 (CC BY-NC-ND).y Our results show that indigenous knowledge about medicinal 1 To whom correspondence may be addressed. Email: [email protected] plants exhibits a strong pattern of linguistic uniqueness in all This article contains supporting information online at https://www.pnas.org/lookup/suppl/ regions, with 73%, 91%, and 84% of the medicinal services in doi:10.1073/pnas.2103683118/-/DCSupplemental.y North America, northwest Amazonia, and New Guinea being Published June 8, 2021. PNAS 2021 Vol. 118 No. 24 e2103683118 https://doi.org/10.1073/pnas.2103683118 j 1 of 5 Downloaded by guest on September 29, 2021 Fig. 1. Medicinal plant knowledge and its association with indigenous languages. The figure illustrates a regional pharmacy with remedies (jars with plants) cited by languages (jar labels). In this paper, we assess to what degree the knowledge contained in this pharmacy would be eroded by the extinction of either indigenous languages or plants. Once we have quantified the overall amount of unique knowl- three regions (Fig. 3; SI Appendix, Table S1). This indicates that edge, we next proceed by mapping how it is distributed across the when planning for medicinal knowledge conservation, the entire linguistic phylogeny. This will serve to identify whether unique linguist spectrum—rather than a few “hot” branches—needs to knowledge is uniformly distributed across all linguistic groups be considered. or whether a few linguistic groups deserve more protection than So far, we have focused on how unique knowledge is dis- others. First, we built language phylogenies for all of the indige- tributed along the cultural dimension. Let us turn now to nous languages in our sample. Next, we calculated the degree examine the other component of the indigenous knowledge of phylogenetic clustering of unique knowledge using Pagel’s network (9), namely, the plants. To understand the degree of lambda (λ) (16); values of λ close to one indicate strong phy- threat faced by medicinal plants, we queried the International logenetic clustering, whereas values close to zero indicate data Union for Conservation of Nature (IUCN) Red List of Threat- without phylogenetic dependence. We did not find clustering of ened Species (17). We found conservation assessments for 22%, unique knowledge along the language phylogenies in any of the 31%, and 32% of the medicinal species recorded in North Fig. 2. Most medicinal knowledge is unique to a single language. Histograms depict the number of indigenous languages that cite a medicinal service. (A) North America. (B) Northwest Amazonia. (C) New Guinea. Red bars show medicinal plant services only known to one language. Dots within the maps indicate the distribution of languages. 2 of 5 j PNAS Camara-Leret´ and Bascompte https://doi.org/10.1073/pnas.2103683118 Language extinction triggers the loss of unique medicinal knowledge Downloaded by guest on September 29, 2021 6 b e n 42 a 2 1 9 1 2 6 6 6 4 47 be 3 4 3 1252 2965 4 wa u h 4 0 h 12 c 12 8 2 uli 0 ABCc n 8 3 1246 k or 1 8 i 1 u s12 2 lus 7 e 12 sout 45 292 2 38 1240 te12 23 1 4 kwak12 2967 m m 9 8 e 1 2 i rt 66 1 h1280 3 lp 2 rt twa 244 o k 4 nu hai 3 4 a 9 1 g heil o 125 e 1240 a n12 1 n 1241 1 k 2 4 1 l1242 3 e no b i1235 ko i126 r12 m p t a t 5 m kas rt2 308 4 ani no 124 ng o w ra lal s e 5 s1 1 s 4 o t 2 im uin 2 e14 1248 c