Rainforests are losing three species every hour American Association for the Advancement of Science

At least three species are becoming extinct each hour in the tropical rainforests, according to a new analysis of man-made extinction by a leading scientist.

Professor Edward O Wilson, a world-renowned evolutionary biologist at Harvard University, made one of the gloomiest predictions to date on the effect ofhuman activity on the world's biodiversity - the thin crust of life that inhabits the outer shell of the planet.

"Humanity has pushed the pace of extinction world-wide to thousands of times faster than the natural rate," he told the annual meeting of the American Association for the Advancement of Science in Atlanta, Georgia. Even on optimistic assumptions, Professor Wilson said, the extent of the "haemorrhaging" in the rainforests meant at least 27,000 species are doomed each year, that is 74 every day and three each hour.

"Most of the populations of organisms, species and races of species, disappear before we can study them, in many cases even before we can provide them with a scientific name."

Professor Wilson said 5 per cent of the world's land surface was burnt each year and tropical forests, the richest repositories of life, were being reduced by about 1 per cent a year.

"They now occupy 6 per cent of the land surface, down by a half from their original cover before the onslaught of humanity."

He cited further examples of mass extinctions caused by human interference, including the loss of 20 per cent of all bird species in the last 2,000 years,and said that more than half of the 266 unique species of freshwater fish living in the Malaysian peninsular have also gone.

Professor Wilson also told the association about 90 types of plants living on a single mountain range in Ecuador which were extinguished by farmers in the space of eight years.

He said the true number of species alive today was unknown and estimates varied between 10 million and 100 million.

Each species played a role in the ecology of the planet and must be preserved not just because they were "masterpieces of evolution" but because of the vital role they played in enriching the soil and in purifying the air we breathe and the water we drink, he said.

"Humanity cannot reduce its forests and fields to a small number of favoured species, and expect to feel safe afterwards."

For more practical reasons there was a need to hold on to "every scrap of biodiversity", he said.

"One of my favourite examples in surgery is cyclosporin, a complex substance derived from an obscure fungus found in Norway. A powerful immunosuppressive agent, it is today the basis of the entire organ-transplant industry."

There is an urgent need to make a world catalogue of species alive today and humanity's goal should be "to carry as much as the rest of life we can through the bottleneck of the next 50 years of [human] overpopulation and environmental destruction," Professor Wilson said.

He added: "It is not too late to make a big difference."