Sorghum hybrids and varieties show similar responses to changing environment, with constant relative yield increases from the hybrids over a wide range of conditions due almost entirely to more florets and grains per plant and per hectare. Carbohydrate production of the leaves of good varieties is probably not much in excess of requirements for filling the grain. The extra spikelet number of the hybrid, increases in photosynthetic area and probably increased photosynthetic efficiency together enable the extra grains be filled. There is also an advantage in size and activity of the root system. The yield increase is strongly buffered against environmental fluctuations. The fact that hybrids can increase over a wide range of farming conditions should result in big increases in production simply by changing from varieties to hybrids, as is already happening in several countries.