Cotton and post-Neolithic investment agriculture in tropical Asia and Africa, with two routes to West Africa

This article provides an up-to-date review of the origins and spread of cottons in the Old World based on archaeobotanical evidence, and explores the routes and socioeconomic context through which cotton cultivation became established across the tropics and sub-tropics of Asia and Africa. Two cotton species were domesticated in the Old World, one of which was grown for millennia as a long-lived tree (Gossypium arboreum) and the other as a shrub over several years (Gossypium herbaceum). While G. arboreum began to be cultivated during the Middle Holocene (7000–4000 years ago) in Pakistan and Northwest India, G. herbaceum was likely domesticated in Africa, perhaps in Sudan. Evidence for cultivation of cotton in Sudan dates from around 2000 years ago, the same period that import of cotton from India into the Roman world was common. The spread of cotton through the African continent involved three trajectories. In southeast Africa, its near coastal islands and Madgascar, received cotton, inferred to be G. arboreum from India, around 1000 years ago in the context of increasing contact across the Indian ocean. As for western Africa, we postulate two dispersal routes: an oasis route through the Sahara and Sahel that focused on G. herbaceum, and a savanna route further south that brought G. arboreum to Cameroon, Benin and Ghana.