title: Seed exchange networks, ethnicity, and sorghum diversity.
abstract: Recent studies investigating the relationship between crop genetic diversity and human cultural diversity patterns showed that seed exchanges are embedded in farmers' social organization. However, our understanding of the social processes involved remains limited. We investigated how farmers' membership in three major social groups interacts in shaping sorghum seed exchange networks in a cultural contact zone on Mount Kenya. Farmers are members of residence groups at the local scale and of dialect groups clustered within larger ethnolinguistic units at a wider scale. The Chuka and Tharaka, who are allied in the same ethnolinguistic unit, coexist with the Mbeere dialect group in the study area. We assessed farmers' homophily, propensity to exchange seeds with members of the same group, using exponential random graph models. We showed that homophily is significant within both residence and ethnolinguistic groups. At these two levels, homophily is driven by the kinship system, particularly by the combination of patrilocal residence and ethnolinguistic endogamy, because most seeds are exchanged among relatives. Indeed, residential homophily in seed exchanges results from local interactions between women and their in-law family, whereas at a higher level, ethnolinguistic homophily is driven by marriage endogamy. Seed exchanges and marriage ties are interrelated, and both are limited between the Mbeere and the other groups, although frequent between the Chuka and Tharaka. The impact of these social homophily processes on crop diversity is discussed.
authors.affiliation: CIRAD (Centre de Coopération Internationale en Recherche Agronomique pour le Développement), UMR AGAP (Amélioration Génétique et Adaptation des Plantes méditerranéennes et tropicales), F-34398 Montpellier, France; vanesse.labeyrie@gmail.com.
authors.forename: Vanesse
authors.initials: V
authors.lastname: Labeyrie
authors.affiliation: INRA (Institut National de la Recherche Agronomique), UMR 0320/UMR 8120 Génétique Quantitative et Évolution - Le Moulon, F-91190 Gif-sur-Yvette, France; FRB (Fondation pour la Recherche sur la Biodiversité), CESAB (Centre de Synthèse et d'Analyse de la Biodiversité), F-13857 Aix-en-Provence, France;
authors.forename: Mathieu
authors.initials: M
authors.lastname: Thomas
authors.affiliation: KALRO (Kenya Agricultural and Livestock Research Organization), GeRRI (Genetic Resources Research Institute), 00200 Nairobi, Kenya.
authors.forename: Zachary K
authors.initials: ZK
authors.lastname: Muthamia
authors.affiliation: CIRAD (Centre de Coopération Internationale en Recherche Agronomique pour le Développement), UMR AGAP (Amélioration Génétique et Adaptation des Plantes méditerranéennes et tropicales), F-34398 Montpellier, France;
authors.forename: Christian
authors.initials: C
authors.lastname: Leclerc
mesh_terms: D018556:Crops, Agricultural / Q000235:genetics*; D018864:Cultural Diversity; D000067565:Farmers / Q000523:psychology*; D014644:Genetic Variation; D006801:Humans; D007630:Kenya; D008037:Linguistics; D012639:Seeds; D060756:Social Networking; D045868:Sorghum / Q000235:genetics*
keywords: crop diversity dynamics; exponential random graph models; local seed systems; social networks analysis; social organization