86 Percent of Earth's Species Still Unknown?
Millions of organisms unnamed as extinction accelerates, study says.
Even after centuries of effort, some 86 percent of Earth's species have yet to be fully described, according to new study that predicts our planet is home to 8.7 million species.
That means scientists have cataloged less than 15 percent of species now alive—and current extinction rates mean many unknown organisms will wink out of existence before they can be recorded.
The study was driven by a simple question: "Are we within reach of finding all species, or are we way off?" said study co-author Boris Worm of Canada's Dalhousie University.
"The answer is, we are way off."
Two hundred and fifty years after Swedish botanist Carl Linnaeus devised a formal system for classifying the diversity of nature, the catalog for some classes of living things—such as mammals and birds—is nearly complete, the study says. But the inventories for other classes are woefully sparse.
For instance, only 7 percent of the predicted number of fungi—which includes mushrooms and yeasts—has been described, and less than 10 percent of the life-forms in the world's oceans has been identified.
What's been discovered so far are "those things that are easy to find, that are conspicuous, that are relatively large," Worm said.
"There is an age of discovery ahead of us when we could find out so much more of what lives with us on this planet."
Counting Earth's Millions
So far, some 1.2 million species are known to science. To calculate the percentage of unknown species, Worm and colleagues first had to answer one of the great questions of ecology: How many species live on the Earth?
Previous guesses ranged from three million all the way to a hundred million. (See "'Encyclopedia of Life' to Catalog All Species on Earth.")
To gain a more precise answer, the authors examined the categories into which all species are grouped.
Scientists lump similar species together into a broader grouping called a genus, similar genera into a still broader category called a family, and so on, all the way up to a supercategory called a kingdom. (See photos of species classification in National Geographic magazine.)
There are five kingdoms: animals, plants, fungi, chromists—including one-celled plants such as diatoms—and protozoa, or one-celled organisms.
Worm's team estimated the total number of genera, families, orders, classes, and phyla—a designation above class—in each kingdom. That's a relatively easy task, since the number of new examples in these categories has leveled off in recent decades.
By contrast, the number of newly discovered species continues to rise sharply.
Using complex statistics, Worm and colleagues used the number of genera, families, and so on to predict Earth's number of unknown species, and their calculations gave them a number: 8.7 million.
An Issue of Statistics
Some experts called the research, published August 23 in the journal PLoS Biology, reasonable.
The new study "takes a hugely clever approach, and I think it's going to turn out to be a pretty important study," said Lucas Joppa, a conservation ecologist at Microsoft Research, the research branch of the software giant.
"If I asked you to count out 8.7 million pennies, that would take you a while, even if you had a whole lot of people doing it."
But Dan Bebber, an ecologist at the environmental group Earthwatch Institute, said the study relies on improper statistical methods.
The study team used a method called linear regression to calculate the number of Earth's species. But Bebber thinks this method is the wrong one for the data, and that the team should have used a technique known as ordinal regression.
As a result, the true number of species could be much higher or lower than 8.7 million, he said.
Nature's Library Disappearing
Overall, formally categorizing a new organism is a lot more complicated than discovering one, study co-author Worm said. Scientists must compare their specimen to museum samples, analyze its DNA, and complete reams of paperwork.
"It's a long process," he said. Most scientists "will describe dozens of species in their lifetime, if they're really lucky."
Unfortunately, extinction rates have accelerated to ten to a hundred times their natural level, Worm added.
(See "Extinctions Overestimated by 160 Percent?")
The information to be gained when new species are discovered "is nature's library, and we've only begun to decipher the first ten books," Worm said.
"We're throwing out entire books without having a look at them."
Go Further
Animals
- How can we protect grizzlies from their biggest threat—trains?How can we protect grizzlies from their biggest threat—trains?
- This ‘saber-toothed’ salmon wasn’t quite what we thoughtThis ‘saber-toothed’ salmon wasn’t quite what we thought
- Why this rhino-zebra friendship makes perfect senseWhy this rhino-zebra friendship makes perfect sense
- When did bioluminescence evolve? It’s older than we thought.When did bioluminescence evolve? It’s older than we thought.
- Soy, skim … spider. Are any of these technically milk?Soy, skim … spider. Are any of these technically milk?
Environment
- Are the Great Lakes the key to solving America’s emissions conundrum?Are the Great Lakes the key to solving America’s emissions conundrum?
- The world’s historic sites face climate change. Can Petra lead the way?The world’s historic sites face climate change. Can Petra lead the way?
- This pristine piece of the Amazon shows nature’s resilienceThis pristine piece of the Amazon shows nature’s resilience
- Listen to 30 years of climate change transformed into haunting musicListen to 30 years of climate change transformed into haunting music
History & Culture
- Meet the original members of the tortured poets departmentMeet the original members of the tortured poets department
- Séances at the White House? Why these first ladies turned to the occultSéances at the White House? Why these first ladies turned to the occult
- Gambling is everywhere now. When is that a problem?Gambling is everywhere now. When is that a problem?
- Beauty is pain—at least it was in 17th-century SpainBeauty is pain—at least it was in 17th-century Spain
Science
- Should you be concerned about bird flu in your milk?Should you be concerned about bird flu in your milk?
- Here's how astronomers found one of the rarest phenomenons in spaceHere's how astronomers found one of the rarest phenomenons in space
- Not an extrovert or introvert? There’s a word for that.Not an extrovert or introvert? There’s a word for that.
- NASA has a plan to clean up space junk—but is going green enough?NASA has a plan to clean up space junk—but is going green enough?
Travel
- Germany's iconic castle has been renovated. Here's how to see itGermany's iconic castle has been renovated. Here's how to see it
- This tomb diver was among the first to swim beneath a pyramidThis tomb diver was among the first to swim beneath a pyramid
- Dina Macki on Omani cuisine and Zanzibari flavoursDina Macki on Omani cuisine and Zanzibari flavours
- How to see Mexico's Baja California beyond the beachesHow to see Mexico's Baja California beyond the beaches
- Could Mexico's Chepe Express be the ultimate slow rail adventure?Could Mexico's Chepe Express be the ultimate slow rail adventure?