A CENTURY AGO American crop scientists began experimenting with the plant known there as corn, and elsewhere as maize. They discovered that by crossing two inbred strains they could create seeds that would consistently grow better than either of the parent plants. It was the beginning of a seed revolution. By the 1940s American agricultural productivity was shooting up; by the 1960s Asia had joined the race, thanks to improved varieties of rice and wheat.

In most of the world, the green revolution continues. Open an American seed catalogue today and you will see dozens of varieties of each plant, many of them labelled “new” to show that they have been released or improved somehow just in the past year.

But on one continent, it never quite happened. African farmers still tend to use open-pollinated seeds held back from the previous year’s crop or commercial hybrids that were developed years ago. That’s one of the main reasons for the continent’s chronically low productivity. The average field planted with maize—Africa’s most important crop, which supplies 30% of people’s calories in some countries—yields a third as much as a Chinese maize field of the same size and just a fifth as much as an American one.

The problem is not a paucity of science. Although crop research in Africa is not as well funded as it is in rich countries, there is enough public and private investment to ensure a stream of new seeds to suit local soils and climates. Nor is the problem ideology. African governments have mostly ignored the arguments, from some charities, that old-fashioned farming is best and that wicked, profit-seeking seed firms should be barred. They know that modern seeds make farming more productive.