Sunday, January 24, 2010

Why Ireland Has No Snakes

Legend has it that St. Patrick drove all the snakes from Ireland. Sometime back in the fifth century he stood on a hill, the story goes, and used a staff to herd the slithering creatures into the sea, banishing them for eternity. It's true, aside from zoos and pets, there are no snakes on the emerald isle. In fact, there never were any snakes in Ireland. This state of affairs probably has more to do with the vagaries of geography than any neat tricks performed by St. Patty.
Snakes first evolved from their lizard forebears about 100 million years ago during the late juvenile emerald tree boaCretaceous period, about the same time that Tyrannosaurus rex first appeared. Early snakes were small and wormy, resembling modern blindsnakes (suborder Scolecophidia). Ancient snake fossils are found only on southern continents, suggesting that snakes first radiated from Gondwanaland—a former supercontinent comprised of modern-day Antarctica, South America, Africa, India, and Australia. Migrating to Ireland wasn't an option at this time, as the area was completely underwater. The chalky sediments that would eventually become the 700-foot Cliffs of Moher on Ireland's west coast were being laid down at the bottom of the sea.
During the Cenozoic era, beginning 65 million years ago, the world's climate gradually began to dry out, and vast tracts of grasslands and other open habitats came to dominate much of the northern hemisphere. Large dinosaurs went extinct, opening the door to new groups of animals. By the Eocene epoch, 50 to 35 million years ago, the predecessors of boas and pythons (called the basal Macrostomatans) were widespread throughout the northern hemisphere. Explosive radiation of snakes in the suborder Colubroidae, including vipers and cobras, occurred during the Miocene epoch, 25 million years ago. Now snakes are found in deserts, grasslands, forests, gaboon vipermountains, and even oceans virtually everywhere around the world. Everywhere except Ireland, New Zealand, Iceland, Greenland, and Antarctica, that is.
One thing these few snake-less parts of the world have in common is that they are surrounded by water. New Zealand, for instance, split off from Australia and Asia before snakes ever evolved. So far, no serpent has successfully migrated across the open ocean to a new terrestrial home. As the world's oceans have risen and fallen over the millennia, land bridges have come and gone between Ireland, other parts of Great Britain, and the European mainland, allowing animals and early humans to cross. However, any snake that may have slithered it's way to Ireland would have turned into a popsicle when the ice ages hit.
The most recent ice age began about three million years ago and continues into the present. Between warm periods like the current climate, glaciers have advanced and retreated more than 20 times, often completely blanketing Ireland with ice. Snakes, being cold-blooded animals, simply aren't able to survive in areas where the ground is frozen year round. Ireland thawed out for the last time only 15,000 years ago. Since then, 12 miles of icy-cold water in the Northern Channel have separated Ireland from neighboring Scotland, which does harbor a few species of snakes. There are no snakes in Ireland for the simple reason that they can't get there.
Snakes and MythsSo where did the myth of St. Patrick and the snakes come from? Most scholars agree that snakes symbolize paganism, which St. Patrick is also credited for banishing from Ireland. Snakes as symbols of evil are prevalent throughout Judeo-Christian mythology, most notoriously in the Garden of Eden as a tempter of Eve. Other societies have viewed snakes with more favor. Snakes were venerated in ancient Egypt, and many gods were represented by snakes, such as the cobra goddess Neith, founder of the universe. More recently, Ben Franklin advocated making a rattlesnake the symbol of the United States.
Mythology aside, herpetologists (scientists who study snakes and other reptiles and amphibians) like to point out that snakes play an important role in many ecosystems throughout the world. Snakes benefit humans by controlling rodent populations, and snake venom has been used to treat various diseases, including cancer, heart disease, and hemophilia. Unfortunately, some 200 species of snakes are considered threatened or endangered, the biggest threat being habitat loss resulting from human activities. Unless humans start taking more of an interest in their survival, real-life snakes may find themselves banished from more places than just Ireland.

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