Only about 150 food plants are used extensively, and 5,000 food plants have ever been used by humans. Indeed, only three species of plants, corn, rice and wheat, supply over half off all human energy needs. However, there is wide agreement that the world's food demands cannot solely rely on these three, though essential plants, particularly as availability of suitable land for their production is declining, research and other methods into increasing their yields are achieving less incremental gains per unit of research and inputs, and population growth continues at an unrelenting pace. There may be tens of thousands of additional kinds of plants that could provide humans food if their properties were fully explored and brought into cultivation, ideally without the dramatic change to the natural environment associated with the cultivation of corn, rice and wheat. Many alternative foods could be found in the tropics, corresponding to a region where many countries have rapidly growing populations.