Humanity depends for its calories and proteins intake on very few crops. Moreover, it has been demonstrated that the diets of the peoples of the different countries are becoming more and more similar worldwide, while the diversity of what they eat is increasing. The reliance on only a few crops is worrying. Similarly, within a crop the diversity is also on the decline.

Farmers are increasingly market oriented. Nevertheless, there are many social, agronomic and ecological reasons why farmers maintain or do not maintain a certain level of diversity, both in their choices for crops and in the cultivars they grow.  Interesting examples are the coexistence of African rice, Asian rice and the interspecific hybrids in some areas of West Africa. This topic also requires synergy with social sciences and is very much related to the theme on seed systems.