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Ahimsa
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The story below indicates how apparently irreducibly complex systems could evolve:
By KENNETH CHANG
Published: April 7, 2006
By reconstructing ancient genes from long-extinct animals, scientists have for the first time demonstrated the step-by-step progression of how evolution created a new piece of molecular machinery by reusing and modifying existing parts.
Dr. Thornton’s experiments focused on two hormone receptors. One is a component of stress response systems. The other, while similar in shape, takes part in different biological processes, including kidney function in higher animals.
The researchers found the modern equivalent of the stress hormone receptor in lampreys and hagfish, two surviving jawless primitive species. The team also found two modern equivalents of the receptor in skate, a fish related to sharks. After looking at the genes that produced them, and comparing the genes’ similarities and differences among the genes, the scientists concluded that all descended from a single common gene 450 million years ago, before animals emerged from oceans onto land, before the evolution of bones.
The team recreated the ancestral receptor in the laboratory and found that it could bind to the kidney regulating hormone, aldosterone and the stress hormone, cortisol.
Thus, it turned out that the receptor for aldosterone existed before aldosterone. Aldosterone is found just in land animals, which appeared tens of millions of years later. “It had a different function and was exploited to take part in a new complex system when the hormone came on the scene,” Dr. Thornton said.
What happened was that a glitch produced two copies of the receptor gene in the animal’s DNA, a not-uncommon occurrence in evolution. Then, for reasons not understood, two major mutations made one receptor sensitive just to cortisol, leading to the modern version of the stress hormone receptor. The other receptor [sensitive to aldosterone] became specialized for kidney regulation.
Dr. Thornton said the experiment refutes the notion of “irreducible complexity” put forward by Michael J. Behe, a professor of biochemistry at Lehigh University.
By KENNETH CHANG
Published: April 7, 2006
By reconstructing ancient genes from long-extinct animals, scientists have for the first time demonstrated the step-by-step progression of how evolution created a new piece of molecular machinery by reusing and modifying existing parts.
Dr. Thornton’s experiments focused on two hormone receptors. One is a component of stress response systems. The other, while similar in shape, takes part in different biological processes, including kidney function in higher animals.
The researchers found the modern equivalent of the stress hormone receptor in lampreys and hagfish, two surviving jawless primitive species. The team also found two modern equivalents of the receptor in skate, a fish related to sharks. After looking at the genes that produced them, and comparing the genes’ similarities and differences among the genes, the scientists concluded that all descended from a single common gene 450 million years ago, before animals emerged from oceans onto land, before the evolution of bones.
The team recreated the ancestral receptor in the laboratory and found that it could bind to the kidney regulating hormone, aldosterone and the stress hormone, cortisol.
Thus, it turned out that the receptor for aldosterone existed before aldosterone. Aldosterone is found just in land animals, which appeared tens of millions of years later. “It had a different function and was exploited to take part in a new complex system when the hormone came on the scene,” Dr. Thornton said.
What happened was that a glitch produced two copies of the receptor gene in the animal’s DNA, a not-uncommon occurrence in evolution. Then, for reasons not understood, two major mutations made one receptor sensitive just to cortisol, leading to the modern version of the stress hormone receptor. The other receptor [sensitive to aldosterone] became specialized for kidney regulation.
Dr. Thornton said the experiment refutes the notion of “irreducible complexity” put forward by Michael J. Behe, a professor of biochemistry at Lehigh University.
