7,000 plant species for food but today around 20 species provide 90 per cent of the global human diet. Of the 7,100 varieties of apple recorded in America a century ago, 6,800 have now been lost. And there are worries, for example, that the maize staple in southern Africa may be under increasing challenge from climate change. Svalbard provides " the last line in the defence against the extincti...