Darwin's Finches Reverse Evolution

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Darwin's finches reverse evolution according to the Royal Society's website Science in the News - Thursday 4 May "Biologists have found that one of Darwin's Galapagos finches has begun to revert to an earlier form because of interference caused by a growing human population. The 'evolution in reverse' study is published in Proceedings of the Royal Society B.

They report "Humans are causing evolution to slip into reverse for one of the finch species that lives on the islands. Scientists have found that the finch is losing the distinguishing trait that was causing it to split into two different species." In the wild, medium ground finches have two distinct forms – large beaked and small beaked - and scientists believe the species was evolving into two different species. However, a team of scientists lead by Andrew Hendry of McGill University have studied finches around human settlements and found many ground finches have intermediate sized beaks. Hendry describes the finding as "evolution in reverse" and goes on to say, "It is an evolutionary split within a species that is being reversed as we think human activity is responsible." What he means is that human activity such as importing plants with intermediate sized seeds, or feeding the birds with rice grains, is giving the intermediate forms a selective advantage. In the wild where there are small and large seeds the small and large beaked birds have a selective advantage over the intermediate beaked birds.

Editorial Comment: There is nothing new in observing Galapagos Finches with intermediate beak sizes. Grange reported in New Scientist 3 July 1999, that fertile hybrids between Darwin's Finch species were common and had "beaks - intermediate in shape." So any change in relative numbers of different ground finch forms due to human pressure may be selection (natural or artificial), but it is not evolution in any direction. The claim that birds with intermediate sized beaks are an "earlier form" is a belief, not an observed fact. From Charles Darwin to the present, Galapagos finches have been observed to have had small, intermediate and large beaks. The variation in numbers of each beak size within the population is not evolution, simply because the finches have not changed. Even if the large and small beaked birds did split into two populations that did not breed with one another, it still would not be evolution – it would simply be the splitting of a larger, more varied population into two smaller, less varied populations. The birds themselves would still be finches. In fact, 150 years of observations of Galapagos Island finches show they are an excellent example of the built in variation within a created kind, enabling living creatures to cope with changes in their environment. If the change in the environment exceeds their ability to copy - they don't evolve - they become extinct!

Evidence News 10th May 2006

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