Millennia ago, Africans began domesticating plants that gave rise to the many crops that have transformed tropical land use and food systems. For instance, the African domesticates sorghum and pearl millet - the world's most drought-tolerant cereals - are important food staples in the semi-arid tropics. Elsewhere, the African oil palm provides the peoples of the humid tropics with a flavourful vegetable oil and, more recently, it has become an indispensable  
ingredient of the processed food and biofuel industries. Africa's kola nut delivers a crucial component of the world's most popular soft drink, while coffee ranks globally as the most consumed beverage. Shea butter's moisturizing qualities and Hoodia gordonii's effectiveness as an appetite suppressant have spurred modern global markets. Both are part of a long history of African exports to Europe that began during the Middle Ages with malagueta pepper and gum arabic. Sorghum and millet reached South Asia 4,000 years ago, having been cultivated in Africa millennia before (Rangan, Carney and Denham, 2012, pp. 311-342). Many domesticates of tropical Asia also came to Africa in prehistory through Indian Ocean trading networks. African farmers adapted taro, plantain, banana, the pigeon pea and sesame to humid tropical regions. Their efforts created new races of plantains and cooking bananas (Musa spp.). Because of such contributions, botanists now recognize Africa as a secondary centre of Musa domestication outside South-East Asia. Africa's botanical endowment also includes many forage grasses vital to raising livestock in the tropics, such as guinea grass (Panicum maximum), Para grass (Brachiaria mutica), molasses grass (Melinis minutiflora), Bermuda grass (Cynodon dactylon), and Jaragua grass (Hyparrhenia rufa) (De Langhe, 1995; Parsons, 1970, pp. 141-53).