New Scientist
Feb. 24, 2002


In the second half of the 20th century, the Earth lost 300,000 species. Humanity has created its own mass extinction...

by Matt Walker

The best guess of biologists is that species are disappearing between 100 and 1000 times as fast as they were before Homo sapiens arrived. But our impact is different from the mass extinctions of the past. They wiped out whole groups of animals, notably the dinosaurs, whereas humans are picking off individual species. In the past, biodiversity recovered as species spread into new ecological niches, but humans are wiping out niches as well as organisms. Wildlife will have a tough time regenerating.

The winners after the mass extinction that finished off the dinosaurs are about to become the losers. One in four mammal species and one in eight bird species face a high risk of extinction in the near future: the population of each species is expected to fall by at least a fifth in the next 10 years. Almost all are endangered by human activity. The invertebrates are tipped to dominate the new world order. Only around 0.1 per cent of the 1.6 million known species are thought to be threatened, though many undiscovered species are likely to be dying out before we even know of their existence.

As global climate change shifts temperatures across the planet, species may not be able follow fast enough. According to UNEP, they will have to migrate 10 times as fast as they did after the last ice age. Many won't make it.

Species that do up and leave will move at different rates, breaking up existing communities. At high latitudes, entire forest types are expected to disappear, to be replaced by new ones. During this transition, carbon will be lost to the atmosphere faster than it can be replaced by new growth, accelerating climate change.

The romantic notion of "wilderness" is fast becoming outmoded. Lee Hannah at Conservation International in Washington DC found that human activity has displaced the natural habitat over two-thirds of the habitable surface of the planet. Much of the undisturbed land is merely rock, ice and blowing sand, already shunned by wildlife.

After habitat destruction, the biggest threat to biodiversity is invasion by alien species. These have arrived mainly through trade, tourism and biocontrol. Invasive plant species already cover 400,000 square kilometres of the US, and are spreading at 12,000 square kilometres a year. At that rate, the whole of the US will fall to outside species within 750 years.

Darwin's laboratory, the Galapagos Islands, now has almost as many introduced species as native ones.

Biodiversity is good for humans. By destroying it, we could bring the axe down on our own heads. Rural communities in more than 60 countries get much of their meat from wild animals. Overpopulation, famine and the spread of high-powered rifles are killing off these creatures. In many areas local people are going hungry. In the Congo basin, conflict has forced people to sell wild meat, putting the squeeze on creatures such as large antelopes, gorillas and chimpanzees. This bush meat trade is growing so fast it will soon be unsustainable, warns Douglas Williamson of the UN Food and Agriculture Organization.

Fewer species will mean fewer potential medicines. Three-quarters of the top 150 prescription drugs in the US are lab versions of chemicals found in plants, fungi, bacteria and vertebrates. The WHO estimates that more than 60 per cent of the world's population relies on plants for primary healthcare. There are 3000 plant species used in birth control alone.

Even if we stop killing species today, nobody reading this will see wildlife restored to its former glory, says Anne Weil of Duke University in North Carolina. Weil and James Kirchner from the University of California, Berkeley, carried out the first comprehensive analysis of mass extinctions and recoveries. The dent already made in biodiversity will take 10 million years to repair itself.