Saturday, August 21, 2010

Earthworm template for human evolution

From NPR's Talk of the Nation:

Historian Christopher Lloyd, who for his new book, What on Earth Evolved, took on the modest assignment of life, specifically the 100 most important species. And we'll give you two quick examples. Stony corals, tiny co-operative fish that constructed reefs that became islands, mountains and habitat for thousands of other creatures, they come in at number seven. And one spot ahead at number six is man.


Family: Lumbricidae

Species: Lumbricus terestris

Rank: 1

Earthworms are annelids, a phylum of creatures whose evolutionary past stretches back at least to the Cambrian Explosion c. 530 million years ago when the trilobites first developed sight and marine creatures evolved bones and shells. Burgessochaeta is an ancestral, twenty-segmented sea worm whose fossils were found by Charles Walcott in the Burgess Shale. Descendants of these marine creatures came ashore at the time of the first invertebrate invasions of the land, c. 450 million years ago, making their living in damp soils broken up by bacteria, fungi and the roots of colonizing plants. These earthworms have been ploughing up the earth, ventilating the soil and nourishing terrestrial ecosystems with their excrement ever since.

Five mass extinctions have occurred over the last 500 million years, some of which devastated up to 96 per cent of all species, but none of them ever touched these creatures. Slice a worm in half and it re-grows as if nothing happened. Divide one half and the same thing happens. One worm even survived forty such butcherings, all in the name of science.

The effects of worms on human history are as profound as they are unwritten. French scientist-cum-poet Andre Voisin was one of the few experts who properly highlighted the role of worms in the birth of ancient human civlizations. 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. Even the Egyptian pyramids, said Voisin, were built thanks to the nourishment of the soil by earthworms. It was only because of their hard-work that farmers could take time off from toiling the soil themselves to work as a labour force for their pharaoh's ambitious building projects.

Throughout human history earthworms have unintentionally but undeniably triggered the rise of civilizations. Wherever earthworms plough, people thrive. When worms perish, societies collapse. Infertile soils led to the demise of the people of ancient Sumeria. Rising levels of salt as a result of irrigating the land with sea water killed off the worms around the mouth of the Euphrates river and the soil turned sour. By 2000 BC their civilization was so weak from lack of food that they fell easy prey to Assyrian invaders from the north.

It might be easy to think that worms matter little today, replaced by artificial fertilizers and pesticides that guarantee soil fertility anywhere and everywhere they are spread. But no. Once again it was largely thanks to the earthworm that the unsustainable nature of using such methods was originally exposed.

But which worm species has had most impact? There are some 15,000 species of segmented worms in the annelid phylum, including leeches, and marine polychaetes — as well as earthworms. They range from the now rare but enormous purple-headed Giant Gippsland (Megascolides australis), a native Australian worm that grows up to three metres long, to the extremely common red wrigglers (Eisenia foetida), vermicultural alchemists that turn kitchen vegetable scraps into rich garden compost.

Lumbricus terrestris, the European earthworm, is now probably the most prolific and invasive species in the world. Its success is largely thanks to the spread of Europeans from c. 1600 onwards. Immigrant farmers inadvertently brought these earthworms, sometimes called 'night-crawlers', to the Americas 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.

Whatever they lack in glamour, colour or a sense of adventure (most worms move only about fifty metres in their four-year lifetime) they make up for in their constant ploughing, harrowing, fertilizing and recycling of that most precious of all the planet's assets — the living Earth itself.

Oh, and btw, humans are on the list because of anthropogenic climate change and for no other attribute.

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