Modelling ancient areas for date palms (Phoenix species: Arecaceae): Bayesian analysis of biological and cultural evidence

Abstract

The date palm (Phoenix dactylifera L.) yields food, medicines, and materials which are useful for building and handicrafts. Other Phoenix species present similar uses. Our aim is to build a model of Phoenix expansion that can be linked to domestication processes. Paleontological and archaeobotanical evidence concerning date palm is extremely diversified around the Mediterranean Basin and in West Asia, mainly consisting of date fruit remains, but also leaf fragments and other plant remains. This biological evidence is further compared with cultural evidence (coinages, pottery, ancient texts) and the present distribution of Phoenix spp. in the area. Bayesian methods working with likelihood and conditional probabilities are successfully applied to generate a model for displaying in maps the ancient distribution of palm groves in terms of probabilities. The model suggests the domestication of Phoenix dactylifera occurred mainly to the east of 30º E Long., and most likely in the Jordan Valley area, starting before 7 ka and, in a millenary westward shift, it was gradually superposed onto pre-existing local western populations of the same genus, especially in the Nile valley. It seems that this mainly affected the Phoenix dactylifera western cluster (P. excelsior, P. atlantica, P. iberica). However other persisted as independent species (P. theophrasti, P. canariensis).