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Island fire threatens Darwin's tortoises

CONFUSION and delay were the official responses as a 12-day-old fire continued to burn on the largest island in Ecuador's Galapagos archipelago. There were reports - and denials - that several rare giant tortoises had already died in the flames.

It is feared that by this weekend the fire on Isabela island could spread the six miles north to the volcano where the tortoises nest. Authorities are considering using tractors to move the colony of 6,000 tortoises, which can weigh up to 550lb each. Some of them may have been alive when Charles Darwin visited the archipelago in 1835.

The Galapagos Islands have become one of the most hallowed places on Earth for biologists, because of the inspiration they provided to Darwin after his five-year voyage on HMS Beagle, which had set sail in 1831 with him as the ship's naturalist.

It was here that Darwin rode on the back of the giant tortoises and noted the unusual flora and fauna of the islands. Animals and plants on islands often illustrate how one species can change over time into two or more species, an essential step in the process of evolution.

Darwin was able to recognise the different types of giant tortoises living on the different islands of the Galapagos from the patterns on their shells. This led him to speculate that the species was not immutable after all, and that it could change over time by diverging from common ancestors.

An even better example of this are the 13 species of finches on the Galapagos, called 'Darwin's finches' because he was the first to record their distinctive characteristics.

Each species of finch - whose fate in the fires has not been reported - is uniquely adapted to exploit a particular food source. They are the classic example of an evolutionary phenomenon called 'character displacement', when animals avoid competing for the same resources in the same area by having slighty different lifestyles, a process known as 'adaptive radiation'.

'The classic example of character displacement is the change in bill size and food habits of Darwin's finches,' writes Edward Wilson, an eminent Harvard biologist, in his book, The Diversity of Life. 'Finches with thick bills are well equipped to rip open tougher fruits and crush bigger and more brittle seeds. Finches with thin bills are limited to softer fare, but they are compensated by an ability to probe narrow crevices and manipulate small objects.'

Although Darwin was the first to note the differences in bill size and shape of the finches of the Galapagos, his collections were not systematic enough to be of much use in formulating the explanations scientists have now arrived at.

Another brilliant naturalist, David Lack, who died in 1973, documented in meticulous detail the beak shape, body size and plumage of the finches. Although he had determined that they belonged to 14 separate species, the striking similarities in appearance and behaviour left little doubt that they had all evolved from a common species.

The finches and giant tortoises of the Galapagos have to this day provided evolutionary biologists with fertile research material on natural selection. Peter Grant at Princeton University, for example, has studied how the finches' bill shape and their size became even more exaggerated when different species lived on the same island; competition is the key factor driving evolution.

Darwin's finches are the premier example of an evolutionary truism: a consequence of natural selection is that two similar species will compete with each other, and the one that does better will eventually eliminate the other - unless it diverges and adopts a different lifestyle.

The moral of the Galapagos - whether it relates to a giant tortoise or a finch - is adapt and survive.

(Photograph omitted)