Crop genetic diversity is still concentrated mainly in centres of diversity and located in the developing world. Farmers in these areas helped preserve genetic diversity by cultivating local varieties, so-called land races, selected over many generations. Land races and their wild relatives, which are the closely related species that survive in the wild, are the richest repositories of crop genetic diversity. Genetic diversity in agriculture provides crops and animals with ability to adapt to ever-changing needs and conditions such as drought, inundation, poor soils and pest diseases. Presently, there is a threat to the world food security due to genetic erosion.
Modern varieties have immunity to specific races of pests.
The initial resistance of modern varieties induce farmers to their exclusive use. Consequently, there is a decrease of stability in the next generations, making them vulnerable to pests and diseases. One of the most serious effects on the stability of farming systems is when pests overcome crops' resistance. Many of the varieties being lost may contain genes that breeders and biotechnologists could have used to develop even more productive varieties or to improve resistance to diseases. A similar pattern of genetic erosion and increased vulnerability is occurring among domesticated animals due to the highly specialized nature of modern livestock production.