Ecologists revise debate on extinctions

Sir Robert May with a koala bear, an endangered species

Two Oxford ecologists have challenged the prevailing view that the ever-increasing rate of species extinction, caused by activities such as the clearance of tropical rain forests, is of particular evolutionary significance or concern. Professor Sir Robert May, the Government's Chief Scientist, currently on leave from his post as Royal Society Research Professor, and Dr Sean Nee, Lecturer in Zoology and Fellow of Lady Margaret Hall, argue in a recent joint paper in Science that approximately 80 per cent of the so-called `tree of Life' can survive even when approximately 90 per cent of species are lost. The `tree' in question arises from evolutionary history. As species evolve over millions of years new ones split off from established ones like twigs from a branch. When a species becomes extinct—as often happens naturally—the branch becomes a dead end. But species which have split off earlier, survive, and they in turn split off as new species, thereby founding a new branch. `All the world's surviving species can be envisaged as all the outermost twig ends on the outermost edge of the tree—with many more dead ends further in,' says Dr Nee. Together these species represent all the life that has gone before them. The paper argues that much of the tree can survive `even vigorous pruning'. The great `breakthroughs' of life—inventions as diverse as feathers, shells, fur, and carapaces—will carry on. Dr Nee said that arguments for species preservation based on abstruse phylogenetic relationships were really missing the point. Attention should instead be focused on the political and socio-economic factors behind global warming, which was likely to be far more damaging in ecological and evolutionary terms than extinction of species. `If there is a man-made mass extinction, as now seems certain, there will still be a sufficient diversity of species to allow evolution to continue,' he said.