From cumulative cultural transmission to evidence-based medicine: evolution of medicinal plant knowledge in Southern Italy

Abstract

In Mediterranean cultures written records of medicinal plant use have a long tradition. This written record contributed to building a consensus about what was perceived to be an efficacious pharmacopeia. Passed down through millennia, these scripts have transmitted knowledge about plant uses, with high fidelity, to scholars and laypersons alike. Herbal medicine's importance and the long-standing written record call for a better understanding of the mechanisms influencing the transmission of contemporary medicinal plant knowledge. Here we contextualize herbal medicine within evolutionary medicine and cultural evolution. Cumulative knowledge transmission is approached by estimating the causal effect of two seminal scripts about materia medica written by Dioscorides and Galen, two classical Greco-Roman physicians, on today's medicinal plant use in the Southern Italian regions of Campania, Sardinia, and Sicily. Plant-use combinations are treated as transmissible cultural traits (or "memes"), which in analogy to the biological evolution of genetic traits, are subjected to mutation and selection. Our results suggest that until today ancient scripts have exerted a strong influence on the use of herbal medicine. We conclude that the repeated empirical testing and scientific study of health care claims is guiding and shaping the selection of efficacious treatments and evidence-based herbal medicine.

Keywords: De Materia Medica; causal effect; cultural transmission and evolution; evidence-based; globalization; herbal medicine; historical ethnopharmacology; traditional medical knowledge.

Figure 1

Map of Campania and adjacent regions indicating considered field studies addressing popular medicinal plant use. 1, Roccamonfina, Caserta (Antonone et al., 1988); 2, Caserta, Caserta (De Feo et al., 1991); 3, Peninsula Sorrentina, Napoli/Salerno (De Feo et al., 1992); 4, Coast of Amalfi, Salerno (De Feo and Senatore, 1993); 5, Monte Vesole and Ascea, Salerno (Scherrer et al., 2005); 6, Montecorvino Rovella, Salerno (De Natale and Pollio, 2007); 7, Sannio area, Benevento (Guarino et al., 2008); 8, Phlegraean Fields Regional Park (Motti et al., 2009); 9, Amalfi Coast (Savo et al., 2011); 10, National Park of Cilento and Vallo di Diano (Di Novella et al., 2013); 11, Rotonda, Pollino National Park (Di Sanzo et al., 2013).

Figure 2

Map of Sardinia indicating considered field studies addressing popular medicinal plant use. 1A, Campidano; Cagliari (Bruni et al., 1997); 1B, Urzulei, Ogliastra (Bruni et al., 1997); 2, Sarrabus, Cagliari (Palmese et al., 2001); 3A, Escolca, Cagliari (Loi et al., 2005); 3B, Lotzorai, Ogliastra (Loi et al., 2005); 4, Marganai, Carbonia-Iglesias (Ballero and Fresu, 1991); 5, Monteleone, Sassari (Ballero and Poli, 1998); 6, Seui, Ogliastra (Ballero and Fresu, 1993); 7, Fluminimaggiore, Carbonia-Iglesias (Ballero et al., 2001); 8, Villagrande Strisaili, Ogliastra (Loi et al., 2004); 9, Tempio Pausania, Olbia-Tempio (Ballero et al., 1997); 10, Laconi; Oristano (Ballero et al., 1997); 11, Arzana, Nuoro (Ballero et al., 1994); 12, Perdasdefogu, Ogliastra (Ballero et al., 1997); 13, Ussassai; Ogliastra (Ballero et al., 1998); 14, Carbonia-Iglesias (Atzei et al., 1994); 15, Gallura; Olbia-Tempio (Atzei et al., 1991); 16, Villasimius, Cagliari (Ballero, 1982); 17, Dorgali (Camarda, 1990); 18, Monte Ortobene, Nuoro (Signorini et al., 2009).

Figure 3

Map of Sicily indicating considered field studies addressing popular medicinal plant use. 1, Mistretta; Messina (Lentini and Raimondo, 1990); 2, Mussomeli; Caltanissetta (Amico and Sorge, 1997); 3, Cesarò; Messina (Barbagallo et al., 1979); 4, Erice; Trapani (Lentini and Aleo, 1991); 5, Pantelleria; Trapani (Galt and Galt, 1978); 6, Madonie, Palermo (Raimondo and Lentini, 1990); 7, Eolie, Messina (Lentini et al., 1995); 8, Pelagie, Agrigento (Lentini et al., 1996); 9, Trapani (Lentini, 1987); 10, Mazara del Vallo; Trapani (Lentini et al., 1987–1988); 11, Egadi; Trapani (Lentini et al., 1997); 12, Riserva Naturale Dello Zingaro; Trapani (Lentini and Mazzola, 1998); 13, Ustica; Palermo (Lentini et al., 1994); 14, Bivona, Agrigento (Catanzaro, 1970); 15, Sant'Angelo Muxaro, Agrigento (Lentini, 1996); 16, Bronte, Catania (Arcidiacono et al., 1999); 17, Monterosso Almo, Ragusa (Napoli and Giglio, 2002); 18, Mezzojuso, Palermo (Ilardi and Raimondo, 1992); 19, Sicilia centro-orientale (Barbagallo et al., 2004); 20, Alcara Li Fusi e Militello Rosmarino, Messina (Arcidiacono et al., 2007); 21, Madonie Regional Park (Leto et al., 2013).

Figure 4

Causal model assuming that Dioscorides and Galen influenced contemporary medicinal plant use considering the confounding variables “plant taxon,” “geography,” “therapeutical use” and their interactions (segments). Arrows indicate the direction of the influence, which may exert a causal effect.

Figure 5

Overall posterior distribution of the causal effect of Dioscorides and Galen on the contemporary plant use traits over all 87 taxa, 11 uses-categories and for all three regions together. The plot shows the mean effect (point) along with the 95% credible interval.

Figure 6

Posterior distribution of the causal effect of Dioscorides and Galen on the contemporary plant use traits of the 87 taxa conditioned by the region of Campania, Sardinia, and Sicily. The plot shows the mean effect (point) along with the 95% credible interval.