As we observe the 150th anniversary this month of the first publication of Charles Darwin's On the Origin of Species, a new book reviews evolution and ranks the top one hundred most influential species of all time.

Homo sapiens is not at the top of the list.

In fact, we humans, who like to imagine that we are the masters of the universe, don't even rank in the top five.

The most influential species (defined as the species that has most changed life on Earth) is ... the earthworm.

Photo courtesy USDA

"According to Charles Darwin, no living thing has had such a profound impact on history as has the earthworm," says Christopher Lloyd, a history scholar at Cambridge University, UK, and author of What on Earth Evolved?: 100 Species that Changed the World (Bloomsbury, November 2009, $45).

After considering the most important species that evolved before the ascent of human civilization, from the beginning of life on Earth until about 12,000 years ago, and then mulling all the species that have been successful since 12,000 years ago--that is the species that have flourished because of modern humans--Lloyd finds that he agrees with Charles Darwin: The earthworm is indeed the most influential species in the history of the planet.

Descendants of sea worms that existed five hundred million years ago, earthworms came ashore with the first invertebrate invasions of the land, making their living in damp soils broken up by bacteria, fungi and the roots of colonizing plants, Lloyd writes. "These earthworms have been ploughing up the earth, ventilating the soil and nourishing terrestrial ecosystems with their excrement ever since."

The survivors of five mass extinctions, earthworms have had profound impacts on human history, Lloyd says.

"Were it not for their continuous regeneration of soils around damp river valleys such as the Nile, Indus, and Euphrates, early agricultural societies in Egypt, India, and Mesopotamia could never have succeeded in building humanity's first large-scale urban communities." 

"Wherever eathworms plough, people thrive. When worms perish, societies collapse."

Throughout human history earthworms have unintentionally but undeniably triggered the rise of civilizations, Lloyd adds. "Wherever eathworms plough, people thrive. When worms perish, societies collapse."

The European earthworm (Lumbricus terrestris) is probably the most prolific and invasive species in the world, Lloyd says.

"Its success is largely thanks to the spread of Europeans, c. 1600 onwards.

"Immigrant farmers inadvertently brought these earthworms, sometimes called 'night crawlers,' in everything from the soil in their potted plants and their horses' hooves, to the treads of their boots and the wheels of their wagons.

"Today there is hardly a region of North America where Europe's earthworms have not made a home for themselves. There they continue to plough, ventilate and fertilize the soil to the general benefit of life in and on the Earth."

Before Man, After Man

What on Earth Evolved? is divided into two sections--Before Man and After Man. Starting with the early Earth, when loose strands of genetic code swarmed the planet, Lloyd explores the most significant lifeforms that evolved in the deep oceans and then wriggled ashore to become pioneers of life on land. In the second section, the author shows how co-evolution of humans and numerous other key species transformed Earth over the past 12,000 years.

A newspaper science and technology correspondent in a previous career, Lloyd has produced an accessible read, guiding the reader through capsule biographies of a hundred of the most influential species. They include slime, sea scorpions, dragonflies, potatoes, ants, tulips, sheep, dogs, cats, coca, opium, poppies, and grapes.

He ranks the species into a table of influence, revealing those that have most changed life on Earth. Academics will no doubt debate the selection and process, but Lloyd makes a compelling, albeit concise, case for each species. The full list of the hundred most influential species may be seen on the book's Web site, or in the book itself.

Covering all of life in one book would be impossible, of course, but Lloyd has taken an interesting approach to some of the most marvelous products of evolution, leading to renewed appreciation of how much life has succeeded through both competition and collaboration.

Here is Lloyd's top ten most influential species of all evolution:

Evolution's top ten species

1. Earthworm
Made it possible for humans to cultivate the planet, settle, and build civilizations.

2. Algae
Without the countless forms of microscopic algae, larger forms of sea life would never have been able to evolve. All land plants are descended from ancestral forms of algae.

3. Cyanobacteria
Plants, trees, and animals all owe their existence to the presence of oxygen in the atmosphere and oceans, supplies of which were originally established by cyanobacteria, a photosynthesizing bacterium that breaks down carbon dioxide and excretes oxygen.

4. Rhizobia
Organisms capable of "fixing" atmospheric nitrogen into soluble nitrates that fertilize the soil so that plants and trees can thrive.

5. Lactobacillus
Bacteria that live inside the human colon, providing beneficial services such as assistance with digestion of milk and protection against harmful bacteria and organisms such as viruses and fungi.

6. Homo sapiens
Humans did not crack the No. 1 position on Lloyd's list, but we merit five pages in his 416-page book and we are the only mammal in the top 10. We lose points chiefly as a result of our recent evolutionary emergence.

We may not rank as the most influential species in this analysis, but our impact pervades the past 12,000 years as we learned to farm animals and plants and harness mch of the resources of the planet.  In that time humans have had a profound impact on many other species, nurturing those useful to us and driving many that are of little value to us into isolation and even into extinction. Our impact on evolution is clearly in its early phases.

7. Stony corals
Coral reefs are powerful places for the natural conservation and co-operation of species, resulting in the construction of massive undewrwater mountains that house an extraordinary diversity of life.

8. Yeast
It is almost exclusively thanks to the action of this single-celled microscopic fungus that humanity has been able to enjoy everything from leavened bread to fine wine. Some of our best prospects for fuelling sustainable industrialization and transportation in the future are based on ethanol, a by-product of yeast.

9. Influenza
One of humanity's biggest ever killers and still the largest threat to populations on Earth.

10. Penicillium
A naturally occurring antibiotic that has transformed modern medicine and substantially increased human populations.

Bloomsbury Publishing provided a copy of What on Earth Evolved? for this entry.

Our ancestors underwent a previously unknown stage of evolution over more than a million years before "Lucy", the iconic early human ancestor specimen that walked the Earth 3.2 million years ago," National Geographic Magazine science editor Jamie Shreeve reports today.

Ardipithecus ramidus, a hominid species that lived 4.4 million years ago in the Afar Rift region of northeastern Ethiopia. This is now the earliest skeleton known from the human branch of the primate family tree, scientists say. "The human branch constitutes the zoological family 'Hominidae;' 'hominids' include Homo sapiens as well as all species closer to humans than to chimpanzees and bonobos, our closest living relatives," according to the journal Science.  The discoveries provide new insights into how hominids might have emerged from an ancestral ape, scientists say.

Illustration courtesy J. H. Matternes via Science/AAAS 

The finding, published in tomorrow's journal Science, is based on the discovery of the oldest fossil human skeleton, a small-brained, 110-pound (50-kilogram) female of the species called Ardipithecus ramidus.

"The fossil puts to rest the notion, popular since Darwin's time, that a chimpanzee-like 'missing link,' midway resembling something between humans and today's apes, would eventually be found at the root of the human family tree," Shreeve writes.

"Indeed, the new evidence suggests that the study of chimpanzee anatomy and behavior, long used to infer the nature of ... the earliest human ancestors, is largely irrelevant to understanding our beginnings."

Read the story, see photos, learn more about the fossil from an interactive:

Oldest "Human" Skeleton Found--Disproves "Missing Link" 

PHOTOS: Oldest "Human" Skeleton Refutes "Missing Link"

Interactive: Explore Ardipithecus ramidus

Walking for sex

Jamie Shreeve also launched his new blog today with a related piece on Ardi's sex life. (Ardi is the name scientists have given this fossil).

It is fascinating reading, "especially if you like learning why human females don't know when they are ovulating, and men lack the clacker-sized testicles and bristly penises tk sported by chimpanzees," Shreeve writes. Read the rest of this at:

Did early humans start walking for sex?

Science

In this 200th anniversary year of Darwin's birth, Science is pleased to publish the results of many years of scientific research that suggest an unexpected form for our last common ancestor with the chimpanzees," writes Bruce Alberts, Editor-in-Chief of Science, in an editorial about the research.

"The history of science assures us that powerful new techniques will be developed in the coming years to accelerate such research, as they have been in the past," Alberts writes. "We can thus be certain that scientists will eventually obtain a rather detailed record showing how the anatomy of the human body evolved over many millions of years."

Science cover illustration copyright 2008 T.H. White

Illustration by Chris Foss/NGS

Diamond dust found in 12,900-year-old sediments at six North American sites boosts evidence of Earth's impact with a swarm of comets at that time, researchers reported today.

The discovery supports the theory that an impact with an extraterrestrial object may have contributed to the disappearance of large mammals and the Clovis culture of prehistoric humans, the scientists say.

Rock art photos and map courtesy Jack Pettigrew, University of Queensland

Rock art painted in an Australian cave many thousands of years ago depicts flying foxes not found in modern Australia, scientists report in the December issue of the journal Antiquity.

Fossilized remains of a wasp nest overlying the art tested to be 17,500 years old. That suggests that the paintings were made at least that long ago and perhaps even thousands of years before that during the coldest part of the Ice Age, when low sea levels would have made it easier for migration to Australia of either the bats or of the artists who painted them, the researchers said.

Illustration by Roy Andersen/NGS

The ability to make fire was likely a key factor in the migration of prehistoric hominids from Africa into Eurasia, a researcher at the Hebrew University of Jerusalem's Institute of Archaeology reported today.

Excavations at the Gesher Benot Ya'aqov archaeological site in Israel showed that the occupants of the site -- identified as being part of the Acheulian culture that arose in Africa about 1.6 million years ago -- had mastered fire-making ability as long as 790,000 years ago.

Reconstruction by Kennis & Kennis/Photo by Joe McNally/NGS

Meet Wilma, the first reconstruction of a Neanderthal created using evidence from fossil anatomy and ancient DNA.

Neanderthals were a species of human that became extinct 28,000 years ago. The lifesize model was created to illustrate "The Last of the Neanderthals," the cover article in the October 2008 issue of National Geographic magazine.

The article, written by Steve Hall and photographed by David Liittschwager and Joe McNally, explores what caused Neanderthals, who dominated Eurasia for more than 200,000 years, to vanish in the Ice Age, while our modern human ancestors survived.