Our window on nature's workings

The Galapagos, once important to science because of their biological isolation, are now also a lab for studying the impact of humans on the environment, writes Edward Larson

No place on earth is better known for its connection with science than the Galapagos Islands. Mention Charles Darwin, and the archipelago's fabled finches come to mind. They and the islands' other novel species have transformed a once-desolate place into a favoured destination for scientists and eco-tourists.

The islands' scientific significance did not, however, begin with Darwin's visit in 1835. Long before, a stream of European and US ships sailed through them. Seen through the eyes of naturalists on board, the place made no sense: penguins living on the equator; herds of gigantic land tortoises; cacti as tall as trees; and no land mammals except a few small rodents. If God had created all the species, they wrote in their diaries, why so many odd types in the Galapagos?

It was partly the continuing reports of biological novelties that placed the archipelago on the itinerary of Darwin's voyage aboard the British survey-ship Beagle . Due to the work of earlier naturalists, Darwin went there with his eyes wide open. What he saw changed the course of science.

Before the Europeans' arrival, few plants and land animals could reach the island chain, which has erupted from the sea over the past 10 million years, and fewer still could endure its arid climate and volcanic terrain. Those that did typically came from South or Central America on the prevailing winds and currents. To survive in the Galapagos, they adapted to local conditions and diversified to fill niches not open to them on the mainland. Varieties evolved in short order: marine iguanas, woodpecker finches and cactus trees, to name just three. Half the native plant and animal species are found nowhere else, yet most are distinctly American. "The Galapagos seems a perennial source of new things," Darwin privately mused long before he ever published those thoughts. Its species, particularly its diverse array of mockingbirds and finches, made no sense under older notions of special creation, but Darwin concluded that they made perfect sense if those species had evolved from a few chance American immigrants to fit the harsh Galapagos environment.

The central role played by the Galapagos in Darwin's grand idea made it a place of continuing interest to biologists. In the late 1800s and early 1900s, a series of scientific expeditions visited the archipelago from the US and Britain to try to resolve outstanding questions in evolution theory. "You will carefully go over the entire ground of each island securing birds of at least 50 of a kind," England's fabulously wealthy bird enthusiast Walter Rothschild instructed his collectors, adding that even slight differences in bill or size should be noted. This was the level of detail needed to study evolutionary relationships using preserved specimens.

These expeditions netted boatloads of Galapagos specimens for research museums in San Francisco, London, Washington and New York. As a result, western science possessed more comprehensive collections from the Galapagos than from nearly any other place in the Pacific - but they could raise more questions than they answered.

The archipelago's finches posed the greatest puzzle. "Such remarkable extremes of variation in bill structure as are seen," a leading US ornithologist wrote in 1931, "lie outside my experience with any North American mainland bird."

A century earlier, seeing such diversity among Galapagos finches had inspired Darwin's thoughts about evolution - but when he could not trace his specimens to separate islands, he turned to Galapagos mockingbirds (which more neatly divide into island-specific types) as better evidence for his theory. Each of them surely had evolved in isolation, Darwin postulated. Later expeditions deepened the mystery of the finches: everyone reported finding different types living together, yet evolution by natural selection suggested that only the fittest of these species should survive.

"There is no group of birds in the whole world which has more right to occupy the attention of zoologists at the present moment," British Museum ornithologist Percy Lowe asserted in 1934, "properly qualified investigators (should) be sent to the Galapagos with the sole object of studying (them) on the spot." Julian Huxley, then secretary of the Zoological Society of London and a leading advocate of natural selection as the driving force of evolution, knew just the person for this job - David Lack.

A 25-year-old English school teacher at the time, Lack had come to Huxley's attention as a gifted observer of bird behaviour. Huxley arranged for the Zoological Society to pay Lack's expenses for a bare-bones expedition to observe finch behaviour on the Galapagos over an entire breeding season. In 1938, Lack travelled to the islands on a cattle boat and stayed with destitute settlers. Money was tight and food insufficient. One of Lack's companions almost died of dysentery. Despite his discomforts, Lack saw on the Galapagos something that no one had seen before - natural selection at work among finches through inter-species competition.

A complete picture of finch evolution emerged in Lack's classic book, Darwin's Finches . "That Darwin's finches are so highly differentiated suggests that they colonised the Galapagos considerably ahead of the other land birds," Lack wrote. "The absence of other land birdsI allowed them to evolve in directions which otherwise would have been closed to them." Some finches remained ground feeders, others took to the trees for food, and yet others adopted the feeding habits of warblers or woodpeckers. Geographic isolation created island variations among these basic types, just like the mockingbirds. These finches did not remain isolated, but spread into each other's territory. Such encounters further drove the evolution of competing species until they diverged into non-competing ones by fine-tuning their beaks for different foods.

Lack's account became the classic case of evolution in action by the 1950s. Ornithologists followed Lack to the islands to test and extend his conclusions, most notably the British-born scientists Peter and Rosemary Grant. Beginning in 1973 and still continuing, theirs became the most influential field study of evolution in action ever conducted. The Grants have literally watched finch beaks evolve through natural selection in response to drought and flood.

Unpersuaded, some US creationists counter that, at most, the Grants have witnessed only minor changes within the finch population and not the evolution of distinctly different types. For them, God remains the designer of all basic kinds of life.

Creationists are playing defence on the Galapagos, however. Nowhere is more intensive field research being conducted on evolution, and it is not just on finches. Hundreds of scientists visit the islands annually to study its distinctive biology, geology and ecology. For them, the Galapagos offers a uniquely pristine laboratory for fieldwork.

Public attention paid to all this Galapagos science contributes to our sentimental attachment to the place. Every high-school biology student learns about Darwin's finches and television documentaries broadcast images from the islands into every home.

We know these islands from more than just science, though. They have become a popular travel destination - and Julian Huxley played a role here, too. As a founder of Unesco and the World Wildlife Fund after the second world war, Huxley had a vision of a new form of tourism that would take travellers from more developed countries to nature sites in less developed ones, with the goal of global ecological enlightenment. Along with East African game parks, Huxley picked the Galapagos as Unesco's first project. Billed as a peaceable animal kingdom unique in human experience, it became Ecuador's first national park and one of the United Nations' initial World Heritage Sites. Mass eco-pilgrimages began in the 1970s. Travel articles told of a land where visitors could walk among giant tortoises, iguanas and frigate birds. Up to 100,000 tourists now visit the islands each year.

Both science and sentiment have made the Galapagos a focal point for international environmental protection. Over the past half century, international conservation groups have devoted more resources to these islands than any similarly sized region on earth.

If any place should be safe from human despoliation, this is it. Yet earlier this year an oil tanker carrying fuel for tour boats ran aground in the archipelago, and local fishermen rioted for more access to fish in the marine preserve. Drawn mainly by the tourism industry, 20,000 Ecuadorians now call the islands home. A place once important to science because of its biological isolation has become a laboratory for studying the impact of humans on the environment. In this, too, as Darwin once said, the Galapagos remain "a perennial source of new things."

Pulitzer prize-winning historian Edward J. Larson is the author of Evolution's Workshop: God and Science on the Galapagos Islands , published next month by Penguin, price £20.