PUERTO AYORA, Ecuador -- An afternoon stroll down Charles Darwin Avenue captures the rapid evolution of Homo sapiens in the Galapagos.
Ecuadorean rap music blares from the Blowout Bar; an Otavalo Indian peddles Andean wool ponchos outside a new pizzeria; and at a souvenir kiosk tourists pick through T-shirts, including one praising an endemic bird species: "I Love Boobies."
"This town is filling up with bureaucracy and burglars," grumbled Jack Nelson, a California native who owns the Hotel Galapagos. "When I first came here in the 1960s, it was just a wooden schoolhouse on a street of sand."
The human population of the Galapagos has grown from fewer than 3,000 in the early 1960s to about 14,000 today. Two decades ago this isolated archipelago 600 miles west of South America's mainland was declared a national province of Ecuador, a move that threw open doors to unrestricted immigration from the continent.
Providing economic sustenance to colonization, tourism started with a handful of annual visitors in the 1960s, swept past a government target of 25,000 visitors in 1982, and, in 1990, reached the current plateau of 40,000.
Boosters of more growth -- and they are increasingly hard to find -- would argue that there is room for more people here. After all, Hawaii, another Pacific Ocean archipelago, has one million people living in an area twice the size of the Galapagos.
"Before, we used to get two hours of water a day -- now we get half an hour of water every two days," Jorge Sotomayor, a resident of a neighboring island, San Cristobal, said of water faucets that stand dry in his house.
But more than physical limits to growth protect this arid chain of 19 volcanic islands. The Galapagos National Park blocks human settlement from 97 percent of a wilderness archipelago once known as the Enchanted Isles.
The Galapagos, a laboratory for studying biological evolution, has occupied a special place in the hearts of scientists since 1835, when Darwin arrived here aboard the Beagle. After years of pondering what he observed on the islands, the naturalist wrote "Origin of Species."
For millions of years, water currents sweeping off South America's western shoulder made the trip to the Galapagos a one-way voyage for beast and flower.
HTC In 1535, when an expedition led by Tomas de Berlanga, bishop of Panama, made the first known human visit here, he found a strange world where birds and animals had evolved completely without fear of man. Today, 90 percent of the reptiles, 50 percent of the land birds and 45 percent of the higher plants can be found only on these islands.
With the cold Humboldt Current washing an island group that straddles the Equator, the Galapagos is the only place in the tropics inhabited by fur seals. Its bird life ranges from flamingos to penguins. Its landscape ranges from humid marshes to mile-high volcanic peaks.
"Where else can one find, all in one location, relatives of the sunflower that have evolved into trees, gulls which forage at night, lizards which feed on seaweed beneath the ocean surface, tortoises which grow to gigantic proportions, or cormorants which have lost the ability to fly?" Alan White and Bruce Epler wrote in a guidebook for the Charles Darwin Foundation, a private research group based here.
Today's tourist invasion seems benign compared with the festivals of slaughter sponsored by earlier human visitors.
In the 1700s, British and American whalers discovered that Galapagos giant tortoises could survive for more than one year in the hold of a ship without food or water. Stacking live tortoises like casks of brandy, the whalers seized an estimated 200,000, wiping out four of the islands' 15 unique species.
After three decades of work, the Darwin Foundation has restored the giant tortoise population to about 13,000.
The whalers soon discovered that the islands' fur seals were easy prey.
"For years, people thought that the Galapagos fur seal was extinct," said Luis Die, a Spanish biologist and tour guide here. "Then a small band was discovered in the 1930s. Now there are 40,000. The population has fully recovered."
The fur seals that survived must have been the wary ones. Unlike most animal species here, fur seals move away when tourists approach.
In the mid 19th century, human colonization started, bringing a ,, new threat to the ecosystem: imported, domesticated animals. Convinced that food supplies would never arrive from the mainland, prisoners serving sentences in Galapagos penal colonies fostered wild populations of goats and pigs.
Since 1974, guards working for the Galapagos National Park have eradicated goats from six islands. But the fight is considered hopeless in large islands like San Cristobal, where wild goats are believed to number 100,000.
"If you start with the goats, then you can't see the pigs, because the goats eat the vegetation," said Orlando Romero, a tour guide and a veteran of several hunts.
The la0test surge in human colonization has brought a surge in new species: rats, cats, cows, donkeys and dogs.
"In the past 10 years, 100 new fauna species have been introduced," said Chantal Blanton, an American ecologist who directs the Charles Darwin Research Station here. "In the previous 200 years, there were only a handful of new species introduced."
From scientists to politicians, a consensus is growing that a curtain should drop on the 20-year experiment with unlimited Galapagos immigration.
"There is no more land, there is no more drinking water, the topsoil is thin," Raul Flores Viteri, the sole Galapagos member of Congress, said in an interview.
This fall he plans to submit to Ecuador's Congress a constitutional amendment that would allow Ecuadoreans to freely travel and to freely choose their residence anywhere in the nation, "with the exception of Galapagos Province."