How did the finch birds change over time?
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Few people have the tenacity of ecologists Peter and Rosemary Grant, willing to spend part of each year since 1973 in a tent on a tiny, barren volcanic island in the Galapagos. Even fewer would have the patience to catch, weigh, measure, and identify hundreds of small birds and record their diets of seeds. Show But for the Grants, the rewards have been great: They have done nothing less than witness Darwin's theory of evolution unfold before their eyes. That would have stunned Darwin, who thought natural selection operated over vast periods of time and couldn't be observed. In their natural laboratory, the 100-acre island called Daphne Major, the Grants and their assistants watched the struggle for survival among individuals in two species of small birds called Darwin's finches. The struggle is mainly about food -- different types of seeds -- and the availability of that food is dramatically influenced by year-to-year weather changes. The Grants wanted to find out whether they could see the force of natural selection at work, judging by which birds survived the changing environment. For the finches, body size and the size and shape of their beaks are traits that vary in adapting to environmental niches or changes in those niches. Body and beak variation occurs randomly. The birds with the best-suited bodies and beaks for the particular environment survive and pass along the successful adaptation from one generation to another through natural selection. Natural selection at its most powerful winnowed certain finches harshly during a severe drought in 1977. That year, the vegetation withered. Seeds of all kinds were scarce. The small, soft ones were quickly exhausted by the birds, leaving mainly large, tough seeds that the finches normally ignore. Under these drastically changing conditions, the struggle to survive favored the larger birds with deep, strong beaks for opening the hard seeds. Smaller finches with less-powerful beaks perished. So the birds that were the winners in the game of natural selection lived to reproduce. The big-beaked finches just happened to be the ones favored by the particular set of conditions Nature imposed that year. Now the next step: evolution. The Grants found that the offspring of the birds that survived the 1977 drought tended to be larger, with bigger beaks. So the adaptation to a changed environment led to a larger-beaked finch population in the following generation. Adaptation can go either way, of course. As the Grants later found, unusually rainy weather in 1984-85 resulted in more small, soft seeds on the menu and fewer of the large, tough ones. Sure enough, the birds best adapted to eat those seeds because of their smaller beaks were the ones that survived and produced the most offspring. Evolution had cycled back the other direction.
Print Collector / Getty Images Charles Darwin is known as the father of evolution. When he was a young man, Darwin set out on a voyage on the HMS Beagle. The ship sailed from England in late December of 1831 with Charles Darwin aboard as the crew's naturalist. The voyage was to take the ship around South America with many stops along the way. It was Darwin's job to study the local flora and fauna, collecting samples and making observations he could take back to Europe with him of such a diverse and tropical location. The crew made it to South America in a few short months, after a brief stop in the Canary Islands. Darwin spent most of his time on land collecting data. They stayed for more than three years on the continent of South America before venturing on to other locations. The next celebrated stop for the HMS Beagle was the Galapagos Islands off the coast of Ecuador. Galapagos IslandsCharles Darwin and the rest of the HMS Beagle crew spent only five weeks in the Galapagos Islands, but the research performed there and the species Darwin brought back to England were instrumental in the formation of a core part of the original theory of evolution and Darwin's ideas on natural selection which he published in his first book . Darwin studied the geology of the region along with giant tortoises that were indigenous to the area. Perhaps the best known of Darwin's species he collected while on the Galapagos Islands were what are now called "Darwin's Finches". In reality, these birds are not really part of the finch family and are thought to probably actually be some sort of blackbird or mockingbird. However, Darwin was not very familiar with birds, so he killed and preserved the specimens to take back to England with him where he could collaborate with an ornithologist. The HMS Beagle continued to sail on to as far away lands as New Zealand before returning to England in 1836. It was back in Europe when he enlisted in the help of John Gould, a celebrated ornithologist in England. Gould was surprised to see the differences in the beaks of the birds and identified the 14 different specimens as actual different species - 12 of which were brand new species. He had not seen these species anywhere else before and concluded they were unique to the Galapagos Islands. The other, similar, birds Darwin had brought back from the South American mainland were much more common but different than the new Galapagos species. Charles Darwin did not come up with the Theory of Evolution on this voyage. As a matter of fact, his grandfather Erasmus Darwin had already instilled the idea that species change through time in Charles. However, the Galapagos finches helped Darwin solidify his idea of natural selection. The favorable adaptations of Darwin's Finches' beaks were selected for over generations until they all branched out to make new species. These birds, although nearly identical in all other ways to mainland finches, had different beaks. Their beaks had adapted to the type of food they ate in order to fill different niches on the Galapagos Islands. Their isolation on the islands over long periods of time made them undergo speciation. Charles Darwin then began to disregard the previous thoughts on evolution put forth by Jean Baptiste Lamarck who claimed species spontaneously generated from nothingness. Darwin wrote about his travels in the book The Voyage of the Beagle and fully explored the information he gained from the Galapagos Finches in his most famous book On the Origin of Species. It was in that publication that he first discussed how species changed over time, including divergent evolution, or adaptive radiation, of the Galapagos finches. Watch Now: Profile of Charles DarwinHow did the finch change over time?By the time the Beagle landed, the finches had evolved into more than a dozen species, distinct from each other in size, vocalizations, and, most notably, beak shape. What happened over the course of those two million years to separate these finches into distinct species was the basis of Darwin's theory of evolution.
How did the changes in the finches of the birds happen?Ongoing field studies have documented rapid changes in these birds' beak sizes and shapes in response to sudden environmental variations -- drought, or human disturbances, for example -- yet very few genetic changes have been found that accompany those physical differences between finch species, nor between populations ...
How did Darwin's finches change?Darwin wondered about the changes in shape of bird beaks from island to island. So-called cactus finches boast longer, more pointed beaks than their relatives the ground finches. Beaks of warbler finches are thinner and more pointed than both. These adaptations make them more fit to survive on available food.
How did the population of finches change?How did the finch population change from before the drought to after? According to Figure 1, the average beak depth increased in size and the finch population had more finches with greater beak depths in 1978 than before the drought.
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