Evolution's rapid shrinkage.

Evolution's rapid shrinkage 

Ordinarily, evolution seems to amble along at a snail's pace. But given the opportunity, it can bound ahead. Fossils from an island off the coast of France show that during a mere blink of geologic time about 120,000 years ago, local red deer evolved into dwarf deer measuring only one-sixth the normal size, reports Adrian M. Lister of the University of Cambridge (England) in the Nov. 30 NATURE.

Pygmy versions of deer, hippopotami, elephants and other animals have developed on islands in the Mediterranean, Indonesia, the east Pacific and elsewhere. In most cases, paleontologists believe these creatures descended from isolated colonies of normal-sized animals that swam to the islands. But no one knew how long the transformations took.

Lister was able to time the events on the island of Jersey because this area becomes isolated from the French mainland only for geologically brief periods. During ice ages, when sea levels drop, a land bridge connects it with Normandy. But between the last two ice ages, high sea levels temporarily turned Jersey into an island resembling today's land form. Using dates for high sea levels, Lister calculates that the island phase lasted only 8,000 to 9,000 years and that the dwarf deer must have evolved over fewer than 6,000 years. He describes this time as "geologically extremely short," noting that "mainland European red deer had existed with only minor changes for the previous 400,000 years."

Lister suggests the dwarfs arose from a group of red deer stranded on the island when sea levels rose. Resource limitations and freedom from predators may explain why the small forms succeeded in the isolated environment. The dwarfs went extinct when a drop in sea levels reconnected Jersey with the mainland.