By Donella Meadows
–August 19, 1993–
Species extinction is “a potential biological transformation of the planet unequaled perhaps since the disappearance of the dinosaurs,” says Thomas Lovejoy of the Smithsonian Institution. Biologist E.O. Wilson of Harvard calls the loss of species “the folly our descendents are least likely to forgive us.”
“Pure conjecture,” sniff Julian Simon and Aaron Wildavsky, professors of business and political science respectively. “Utterly without scientific underpinning and … counter to all the existing evidence. Such apocalyptic claims are used to bludgeon the Federal Government for money and action.”
So are species disappearing, or aren’t they? How is an ordinary person supposed to know what, or whom, to believe?
We could begin by checking out the credentials of the arguers. Simon and Wildavsky, and indeed most scoffers about extinction, are not scientists. Lovejoy and Wilson are field biologists, world renowned, regularly out in nature watching what is happening. In my experience, all the people sounding the alarm about extinctions are ecologists, and the doubters are people who wouldn’t know a red-cockaded woodpecker from a cockatoo.
Which proves nothing. Respected scientists have been wrong about a lot of things. Science could be defined as the regular practice of throwing over what respected scientists think. So ultimately you and I have to do more than ask what other people think, we have to think for ourselves.
So think. Can anyone know how many species are going extinct?
No. An extinction is impossible to witness. All you can say is that a certain plant or animal can’t be found any more. Sometimes (rarely) a species thought to be extinct shows up again. Sometimes a species that is alive and well is for all practical purposes extinct. Some giant rainforest trees that remain in cleared cattle pastures will never reproduce, because the bats, birds, or insects that pollinate them are gone. They may live for a century, but one biologist I know calls them “the living dead.”
No one even knows how many species there ARE. About 1.6 million kinds of life have been named. Estimates about how many more are out there range from 3 million to 30 million. Most mammals, fishes, and birds are probably known, but smaller creatures, insects, fungi, bacteria, and viruses are barely explored, and their diversity is mind-boggling.
There are 152 known species of mosquito in Nepal. There may be 10,000 species of bacteria in a spoonful of forest soil, but only about 3,000 in the whole world have names. E.O. Wilson says it’s simple to find a new species — it usually takes him half an hour after arriving in the tropics. Mike Ivie, a beetle specialist from Montana State University, says, “There is no place on Earth — none — where the entire biota is known.”
There aren’t enough field biologists to begin to catalog all the wonders of the living world. And while they are frantically working at the job, their study sites disappear, turning into banana plantations, oil fields, pastures, cities. They don’t know how many species there are, but I’ve never met one who doubts that there are fewer all the time.
Norman Myers was the person who tried to put a number on the rate of disappearance. In the mid-1970s everyone was quoting the rate of species extinction as one a year. Myers knew that number referred only to mammals and birds, and only to named species. The real number had to be much higher. So he reasoned as follows (this is the process labelled “pure conjecture” by Simon and Wildavsky):
– Assume there are 5-6 million species in total,
– 2/3 of them are in the tropics (3.5 to 4 million),
– 1/2 of those are in tropical rainforests (1.75 to 2 million),
– 1/3 to 1/2 of these forests will be gone by the year 2000,
– There is a linear relationship between area of forest destroyed and numbers of species lost,
– Therefore 600,000 to 1 million species will be lost in the rainforests,
– There could be as many as 400,000 species lost elsewhere
– Therefore 1 million is a conservative estimate for total world losses between 1975 and 2000. That averages to over 130 species a day, or about one every 10 minutes.
When Myers published those numbers, he created a shock wave. Some scientists claimed that the extinction rate could not possibly be so high. Others said it’s probably much higher.
The matter is still not settled, but new information suggests that Myers overestimated some numbers and underestimated others. Satellite pictures show the rate of rainforest clearing to be slower than he supposed. But the rate of extinction may be faster, because the forest is being cleared in patches, leaving scattered fragments. Extinction is more rapid, ecologists have shown, in fragmented habitats than in single patches of equal area.
The one point about which there is no doubt is that the human population is expanding at a rate that increases every year. Forests are being leveled, grasslands are being plowed, deserts and cities and roads are spreading. You can see that for yourself.
So back to your common sense. Who has a tougher case to make, those who claim that human expansion eliminates species, or those who claim that it doesn’t? Do we need to know the exact rate at which we are impoverishing nature? Since the earth is finite, and we will have to stop expanding sometime, should we do it before or after nature’s diversity is gone? What is it, do you think, that motivates the people who worry about these questions? What motivates the people who deny their importance?
Copyright Sustainability Institute 1993