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Evolution Faster Than We Thought |
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By Francesca Colombo*
Tierramérica spoke with scientists Peter and Rosemary Grant, who have documented that the process of mutations in finches in the Galapagos Islands is faster than Charles Darwin, father of evolutionary theory, realized.
BERN, Switzerland - Spouses Peter and Rosemary Grant, both 69 years old, have been following the footsteps of Charles Darwin in the Galapagos Islands since 1973. Through meticulous measurements of the beaks of finches and studying their song over several decades, they were able to document the speed of the natural selection process.
Their study focussed on 25 generations of these small birds -- some 19,000 in total -- belonging to 14 finch species on Daphne Island in the archipelago, located 1,000 km from the coast of Ecuador in the Pacific Ocean.
"We proved three things: the first is that the process of natural selection is faster than Darwin thought. We discovered the number of genetic variations in the shape of the beak and the body in the natural populations" of finches, British-born Peter Grant told Tierramérica.
"Second, we documented the mechanism through which different populations of finches can be isolated in reproduction and become new species; and third, that the 14 species in the Galapagos evolved from a common branch of birds that arrived on the islands two or three million years ago," summarized Grant.
For their life work, on Nov. 11 in the Swiss city of Bern, the Grants received the 2005 Balzan Prize for population biology, recognizing their scientific excellence and contribution to the world of science.
"The two scientists explained the mechanisms through which new species emerge and how genetic diversity is maintained in natural populations. The work of the Grants is the most significant study of evolution in recent decades," says the International Balzan Foundation, which awards the prize.
Rosemary and Peter are both biologists and professors at Princeton University in the United States, author of several books, and the subject of another, "The Beak of the Finch: A Story of Evolution in Our Times", written by Jonathan Weiner, winner of the 1994 Pulitzer Prize.
The investigations of the Grants, who are also founders of the Charles Darwin Research Station in the Galapagos, demonstrated that the rapid mutations in the sizes of the body and the beak of the finches in response to availability of food are guided by natural selection.
The concept of natural selection -- part of Darwin's theory of evolution -- maintains that environmental conditions determine the effectiveness of certain traits in living organisms for their survival and reproduction.
The Grants observed, for example, that in years of drought, like 1977, when there were reduced supplies of seeds for the finches to feed on, natural selection favored those with larger and deeper beaks. Many of the smaller finches did not survive.
But this situation changed with the torrential rains that accompanied the climate phenomenon known as El Niño in 1982. The rainfall left small seeds that were the staple of small finches, better suited than their "cousins" with larger beaks. They adapted and reproduced.
"Our investigation studied the process of these adaptations, and we established that these changes occurred in a few years, and are steps towards producing new species of birds," Rosemary Grant, born in Scotland, said in a Tierramérica interview in Bern when she and her husband received the Balzan Prize.
The scientists not only pursued the work started by Darwin (1809-1882) but also confirmed his hypothesis.
Aboard the HMS Beagle, Darwin visited the Galapagos in 1835, and from his studies there, deduced that the diverse species of finches with different beaks were the result of local ecological conditions and natural selection. These theories about how new species formed turned into the basis of his celebrated work "The Origin of Species", published in 1859.
The biologists studied the 14 Darwin finch species, which include small tree finches (Camarhynchus parvulus), sharp-beaked finches (Geospiza nebulosa), vegetarian tree finches (Platyspiza crassirostris), and cactus finches (Geospiza scandens), among others.
For the scientists, the Galapagos finches (black males, brown females), who nest in trees and eat insects, or on the ground and eat seeds and flowers, were the perfect object of study, due to the simplicity of their undisturbed habitat.
"The changes in the environment and the influence of the currents of El Niño and La Niña create a very special situation. The finches are trapped by these conditions and their changes occur more quickly," said Peter Grant.
The Grants also identified gene Bmp4, which influences the development of beak shape, in addition to proving that these species descend from a common branch of finches that reached the Galapagos two or three million years ago.
This gene could play an important role in how these small birds evolved and continue to evolve.
Although they live in the United States, the Grants return to the islands regularly, and plan to continue their research there in January. Their daughter Thalia, also a biologist and scientific illustrator, lives in the Galapagos.
* Francesca Colombo is a Tierramérica contributor.
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