We believe there are between 8 and 50 million species on Earth. We guess we have only named around 4 per cent of them. We also believe we are killing off one plant and 50 animal species every day as we destroy their habitats: that is between a thousand and a million times the natural extinction rate.

We do not have exact figures. But we clearly do not know what we are doing, only that we are killing off many of the world's plants and animals before we even know what they are.

As we do this, we alter the world's ecosystems and lose species with incalculable potential benefits to humankind. That is worrying enough. Worse, we also imperil our food supplies. For the diversity of the Earth's plants and animals is a priceless resource for agriculture.

Farmers improve our main crops by interbreeding them with their wild relatives, gaining genes that naturally resist diseases, insect pests and environmental stresses, and make them more productive. Farmers in Asia breed the junglefowl, ancestor of the domestic chicken, with their own poultry. The markhor, a wild mountain goat, mates with farm goats, keeping them healthy, robust and resilient. The bearded pig in Southeast Asia could be used for its tolerance to heat and tropical disease.

But these wild relatives are lost as natural habitats are wiped out to make way for large-scale cultivation of foreign commercial crops. And the crops themselves often consist of only one variety - and so are particularly vulnerable to mass outbreaks of pests and diseases. An epidemic can wipe out a genetically uniform crop across a whole continent, throwing millions into food insecurity and even famine.

In the 1840s, just such a famine occurred in Ireland, killing a million people, when blight affected the one variety of potato they grew as the mainstay of their diet.

Similarly, in the 1960s and 1970s, the grassy stunt virus killed 3 million tonnes of the Asian rice crop, enough to have fed 9 million people for a year. Plant breeders searched the world for a wild, resistant rice to try to stop further devastation. They eventually discovered two mutated seeds of a variety in Uttar Pradesh, India: it was the only one, among hundreds tested, to be immune to the virus. The vital gene was bred into the IR36 rice cultivar, and is still found today in every high-yielding rice grown in Asia.

What can we do? We can protect diversity by growing a wider variety of crops in the countries where they originate. The yeheb-nut bush from Somalia, eel grass from Mexico and amaranth from the Andes could all provide nutritious food. Some - like the winged bean from Papua New Guinea, which is 40 per cent protein - could improve diets by replacing less nutritious crops.

Some new crops grow in land and conditions unsuitable for other agriculture - and in the conditions that our changing environment may soon bring. Only 8 per cent of the Earth's surface - about 11 million square kilometres - is suited to modern agriculture: far more than this lies unused. But there are plants that can cope with wetter, saltier, colder or drier conditions than our current crops, producing food on as yet uncultivated land. New hybrid forms of sorghum and millet, for example, can grow in areas previously considered too hot and dry. And salt-resistant crops, such as the Galapagos tomato, can grow in salinized land, made too salty by poor irrigation.

Over the last 50 years the world's population has increased by about 3 billion people. Yet, by using science to boost agriculture, we have managed to increase food production to feed most of them.

Biodiversity can help us meet the urgent present need to feed all the world's people. But unless it is preserved it will be much harder to provide food for any of us in the future.

ART BY DEIA SCHLOSBERG/PCI

Related Links:
IRRI (PDF) PDF Version