Darwin's Finches & the Effects of Pollution

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Darwin's Finches & the Effects of Pollution

Darwin's finches show how man harms evolution
By Steve Connor
Published: 04 May 2006
They were the birds that were said to have inspired Charles Darwin to formulate his theory of evolution more than 10 years after his famous visit to the Galapagos Islands.

Darwin's finchesiconically depicted how biological diversity and natural selection lead to the origin of new species - but now scientists have detected signs of evolution "in reverse".

Biologists have found that one of Darwin's finches living in the remote Pacific archipelago has begun to revert to an earlier form because of interference caused by a growing human population. 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 - its beak.

The medium ground finch is normally found in two distinct forms - one with a larger beak the other with a smaller one - but when humans come to live alongside the finch, this "bimodal" beak size tends to disappear.

The scientists believe that the arrival of people on the islands may be causing evolution to run in reverse by causing the two extreme versions of the ground finch to revert to individuals with intermediate beak sizes.

In effect, people appear to be unwittingly eliminating the evolutionary disadvantage of having a beak that is half-way in size between the two extremes, according to a study published in the Proceedings of the Royal Society B. As yet the researchers do not understand why people are having this effect but the implications are that the influx of tourists and migrants to the Galapagos is helping to eradicate a source of biological diversity that has made the islands famous.

Professor Andrew Hendry of McGill University in Montreal, who led the study, said: "We need to make more effort to enable those species that are in the process of diversifying to continue to diversify and thereby generate new species. It is appropriate to describe it as evolution in reverse. It's an evolutionary split within a species that is being reversed and we think human activity is responsible," he said.

Darwin collected many dead specimens of the finches on his visit to the islands in 1835 and in 1845 he began to realise that they may have evolved from common stock. He eventually recognised that it was the size and shape of each finch's beak that determined what it could eat and in which ecological niche it was best suited to survive.

"Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends," Darwin wrote in the 1845 edition of the Journal of Researches.

Intermediate beak sizes for medium ground finches are rarely if ever seen in the wild, which indicates that it is usually a disadvantage to be born with an intermediate beak size.

But when the scientists studied populations of medium ground finches living near to human settlements on the island of Santa Cruz, they found that most of them had reverted to having intermediate-sized beaks.

The researchers can only speculate about the causes of the reverse. It could be the result of people introducing alien plants with intermediate-size seeds, or it could be the deliberate feeding of wild birds with imported rice.

"Humans are changing the nature of the adaptive landscape. They are homogenising it. Being intermediate was once bad for the survival of this finch, now it is no longer the case for birds living near people.

"There's plenty of evidence of humans having caused species to go extinct. We're not, in essence, doing anything to reverse the loss of biodiversity," Professor Hendry said.

They were the birds that were said to have inspired Charles Darwin to formulate his theory of evolution more than 10 years after his famous visit to the Galapagos Islands.

Darwin's finchesiconically depicted how biological diversity and natural selection lead to the origin of new species - but now scientists have detected signs of evolution "in reverse".

Biologists have found that one of Darwin's finches living in the remote Pacific archipelago has begun to revert to an earlier form because of interference caused by a growing human population. 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 - its beak.

The medium ground finch is normally found in two distinct forms - one with a larger beak the other with a smaller one - but when humans come to live alongside the finch, this "bimodal" beak size tends to disappear.

The scientists believe that the arrival of people on the islands may be causing evolution to run in reverse by causing the two extreme versions of the ground finch to revert to individuals with intermediate beak sizes.

In effect, people appear to be unwittingly eliminating the evolutionary disadvantage of having a beak that is half-way in size between the two extremes, according to a study published in the Proceedings of the Royal Society B. As yet the researchers do not understand why people are having this effect but the implications are that the influx of tourists and migrants to the Galapagos is helping to eradicate a source of biological diversity that has made the islands famous.

Professor Andrew Hendry of McGill University in Montreal, who led the study, said: "We need to make more effort to enable those species that are in the process of diversifying to continue to diversify and thereby generate new species. It is appropriate to describe it as evolution in reverse. It's an evolutionary split within a species that is being reversed and we think human activity is responsible," he said.
Darwin collected many dead specimens of the finches on his visit to the islands in 1835 and in 1845 he began to realise that they may have evolved from common stock. He eventually recognised that it was the size and shape of each finch's beak that determined what it could eat and in which ecological niche it was best suited to survive.

"Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends," Darwin wrote in the 1845 edition of the Journal of Researches.

Intermediate beak sizes for medium ground finches are rarely if ever seen in the wild, which indicates that it is usually a disadvantage to be born with an intermediate beak size.

But when the scientists studied populations of medium ground finches living near to human settlements on the island of Santa Cruz, they found that most of them had reverted to having intermediate-sized beaks.

The researchers can only speculate about the causes of the reverse. It could be the result of people introducing alien plants with intermediate-size seeds, or it could be the deliberate feeding of wild birds with imported rice.

"Humans are changing the nature of the adaptive landscape. They are homogenising it. Being intermediate was once bad for the survival of this finch, now it is no longer the case for birds living near people.

"There's plenty of evidence of humans having caused species to go extinct. We're not, in essence, doing anything to reverse the loss of biodiversity," Professor Hendry said.

http://news.independent.co.uk/environment/article361830.ece


Matt-Evolved
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Darwin's Finches & the Effects of Pollution

I've heard of this kind of thing before.

One of my biology professors was saying that because of humans, the overall weight and beak shape of the seagull population has begun to change. The larger weight can be seen as a reversion back to land-confinded birds and the beak change is due to a change in diet (mainly these birds eat garbage and food left by humans).

Sometimes I hope that Bird Flu hits humans pretty hard to put a serious dent in our population. Yeah, I know that sounds harsh, uncaring, and unbrotherly, but the human population is experiencing such exponential growth that the rest of the world is suffering. Everywhere humans put their feet, the local ecosystem gets destroyed. No other species on this planet has such a disastrous effect on their habitat than we do... not even zebra mussels (On a side note, those buggers are tough sons-of-bitches. Even at the Shedd Aquarium in Chicago, they won't use live zebra mussels because they would get into all the water piping and such and thus destroy the whole aquarium).

Sorry if that little comment made you all think that I don't care about other people. I do, but how long is the world going to suffer before it retaliates? Every other species that experiences exponential growth always crashes, look at reindeer.

I think Bird Flu and AIDS has evolved faster than they should have just due to humans large growth. Its mother nature's way of telling us to fuck off.

And she may be right.

"I call Christianity the one great curse, the one great intrinsic depravity, the one great instinct of revenge, for which no means are venomous enough, or secret, subterranean and small enough - I call it the one immortal blemish upon the human race." -