Fill the blank marked (14) in the passage: Most of our food comes from agriculture, so we tend to believe that it is ______ (6) of natural biota. This is not true. In nature, ______ (7) plants and animals ______ (8) to the rigours of natural selection. Only the fittest survive. ______ (9) wild populations have numerous traits for competitiveness, resistance to parasites, ______ (10) to adverse conditions, ______ (11) other aspects of vigour. In contrast, populations grown for many ______ (12) under the pampered conditions of agriculture tend to lose these traits, because they ______ (13) for production, not resilience. For example, a high-producing plant ______ (14) lacks resistance to drought is ______ (15) and the resistance to drought is ignored. Also, in the process of breeding plants for maximum production, all genetic variation is eliminated.