By Sean Henahan, Access Excellence

GAINESVILLE , Fl. (Aug. 23, '96) Human fascination with one of Darwin's best known examples of evolution, the Galapagos, is contributing to the rapid extinction of many rare species on those islands, say researchers.

A University of Florida researcher who retraced Darwin's footsteps reports that humans are overwhelming evolution, wiping out some animal species 300 times faster than new species can evolve.

"Some islands are like a war zone," says David Steadman, curator of birds at the University of Florida's Florida Museum of Natural History. "I discovered that no native animals remain on Easter Island."

In addition to falling prey to hunters, the native species were victims of diseases and animals that humans imported. Rats, mice, cats, dogs, pigs, goats, cattle and donkeys preyed upon the native species and destroyed their habitat.

Steadman has spent a year of his life in 10 trips to the Galapagos Islands. He applies radiocarbon dating, DNA analysis and other modern techniques to study evolution and extinction.

Species extinguished from some of the Galapagos Islands include the famed Galapagos tortoise, the Floreana mockingbird, the sharp-beaked ground finch, the large ground finch, a snake species and the barn owl.

Steadman found even greater destruction than on the Galapagos Islands when he worked on the Polynesian island chain of Tonga. Only 13 of the 27 species of land birds that once inhabited the island remain.

In the Galapagos, Steadman painstakingly studied a cave on Foreana Island. The mile-long cave, which was formed as a pocket in a lava flow, contains rich layers of fossils that developed because of the unusual digestive system of the barn owl, Steadman believes. For thousands of years, owl after owl carried its prey into the recesses of the cave.

After dining on lizards, birds and other prey, the owls vomited the bones onto the floor. The bones have turned into a treasure chest of fossil wonder.

"The beauty of this site is that we can peel off one layer at time, knowing that each succeeding layer is older than the one before it," Steadman says. Steadman carefully collected 7,000 small bone fossils within a single cubic meter of the cave then brought them back to his laboratory to analyze.

In addition to documenting extinction, Steadman has been able to compare ancestors of various island creatures to their modern counterparts.

He observed that some species on the Galapagos have not evolved over the past 10,000 years and some in Tonga have remained the same for more than 100,000 years. "There's almost no change. I can't tell the old bones from the new bones in some species," Steadman says.

"Darwin believed that evolution proceeded at a steady pace over time, but I've found that once some species got a good thing going, they didn't change much."

"Darwin didn't have a single moment in which he proclaimed 'eureka,'" Steadman says. The author of the theory of evolution labored a quarter century between his five-week visit to the Galapagos in 1835 as the naturalist on the ship Beagle and his publication of "On the Origin of Species."

The Galapagos Islands are often used as an example of how animals adapt to their environment. The birds known as Darwin's finches are a prime example. One species' beak is pointed like a woodpecker's in order to probe into crevices and capture insects. Another species' beak is long and narrow to help it suck nectar from flowers. A third has a tough, thick beak that it uses to crush seeds.

Such adaptation was common on the islands because climatic conditions and terrain varied widely, Steadman says. Many animals lacked predators, so they evolved with few defenses.

"Evolution got richer and richer until humans came," Steadman says. "Humans put a monkey wrench in the whole process. After people arrive, the rate of extinction progresses so rapidly that evolution can't keep up with it."

Steadman's work is highlighted on the Discovery Channel special "Galapagos: Beyond Darwin." The show can be seen on Aug. 25, 27 and 31 and Sept. 13.

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