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In single-cell [[organism]]s flagella move like a whip to provide propulsion to the cell. As part of a larger organism, their function is often to move fluids along mucous membranes. When they perform this function, they are called [[cilia]].

In single-cell [[organism]]s flagella move like a whip to provide propulsion to the cell. As part of a larger organism, their function is often to move fluids along mucous membranes. When they perform this function, they are called [[cilia]].

There are three types of flagella: [[eukaryote|eukaryotic]], [[archaeal]] and [[bacteria|bacterial]].  

There are three types of flagella: [[eukaryote|eukaryotic]], [[archaeal]] and [[bacteria]]l.  

The internal structure of eukaryotic flagella is made up of nine microtubule doublets linked by proteins, which form a cylinder around a central pair of microtubules. There are usually only one or two flagella on a eukaryotic cell, and they move in a lashing motion like a whip. One example of this is the [sperm] cell.

The internal structure of eukaryotic flagella is made up of nine microtubule doublets linked by proteins, which form a cylinder around a central pair of microtubules. There are usually only one or two flagella on a eukaryotic cell, and they move in a lashing motion like a whip. One example of this is the [sperm] cell.

==Bacterial Flagellum and Intelligent Design ==

==Bacterial Flagellum and Intelligent Design ==

[[Image:Wm Dembski.jpg|right|150px|thumb|[[William Dembski]]]]

[[Image:Wm Dembski.jpg|right|150px|thumb|[[William Dembski]]]]

The bacterial flagellum has frequently been presented as a counter-example to the [[theory of evolution]]. <ref>Dembski, W. 2002a, No Free Lunch: Why specified complexity cannot be purchased without intelligence. Lanham, Maryland: Rowman & Littlefield.</ref> <ref>Behe, M. 1996a. Darwin's Black Box. New York: The Free Press.</ref> Intelligent design theorists argue that it could not possibly have been produced by an evolutionary pathway.   

The bacterial flagellum has frequently been presented as a counter-example to the [[theory of evolution]].<ref>Dembski, W. 2002a, No Free Lunch: Why specified complexity cannot be purchased without intelligence. Lanham, Maryland: Rowman & Littlefield.</ref><ref>Behe, M. 1996a. Darwin's Black Box. New York: The Free Press.</ref> Intelligent design theorists argue that it could not possibly have been produced by an evolutionary pathway.   

[[Intelligent design]] [[theory|theorist]] [[Willam Dembski]] wrote:

[[Intelligent design]] [[theory|theorist]] [[Willam Dembski]] wrote:

Behe asserts that the flagellum is a structure "in which the removal of an element would cause the whole system to cease functioning" <ref>Behe, M., 2002. The challenge of irreducible complexity, Natural History 111 (April): 74.</ref> and that its individual parts must have been specifically designed to work as a unified assembly.  

Behe asserts that the flagellum is a structure "in which the removal of an element would cause the whole system to cease functioning" <ref>Behe, M., 2002. The challenge of irreducible complexity, Natural History 111 (April): 74.</ref> and that its individual parts must have been specifically designed to work as a unified assembly.  

The argument is that because a minimum number of protein components are needed for a working biological function, evolution could not have selected to produce those components a few at a time, since they do not have functions that natural selection would favor.  The logic of irreducible complexity dictates that these individual components should have no function until all 30 are put into place, at which point the function appears. Behe wrote: " . . . natural selection can only choose among systems that are already working" <ref>Behe, M., 2002. The challenge of irreducible complexity, Natural History 111 (April): 74.</ref>. An irreducibly complex system does not work unless all of its parts are in place. The flagellum is irreducibly complex, and therefore it must have been designed.  

The argument is that because a minimum number of protein components are needed for a working biological function, evolution could not have selected to produce those components a few at a time, since they do not have functions that natural selection would favor.  The logic of irreducible complexity dictates that these individual components should have no function until all 30 are put into place, at which point the function appears. Behe wrote: " . . . natural selection can only choose among systems that are already working".<ref>Behe, M., 2002. The challenge of irreducible complexity, Natural History 111 (April): 74.</ref> An irreducibly complex system does not work unless all of its parts are in place. The flagellum is irreducibly complex, and therefore it must have been designed.  

===The Combinatorial argument===

===The Combinatorial argument===

William Dembski <ref>Dembski, W. 2002a, No Free Lunch: Why specified complexity cannot be purchased without intelligence. Lanham, Maryland: Rowman & Littlefield. </ref> calculated the probability of assembling an object like the flagellum by working out the probabilities that each of its components might have originated, been localized to the same region of the cell, and assembled in the right order by chance.

William Dembski <ref>Dembski, W. 2002a, No Free Lunch: Why specified complexity cannot be purchased without intelligence. Lanham, Maryland: Rowman & Littlefield.</ref> calculated the probability of assembling an object like the flagellum by working out the probabilities that each of its components might have originated, been localized to the same region of the cell, and assembled in the right order by chance.

Dembski states that, given enough time, any event with a probability larger than 10_-150 might well take place. He puts the odds of evolving the 30 proteins of the bacterial flagellum at 20_-30 ("around 10_-39")  and explains that since the flagellum requires 30 such proteins, they "will all need to be multiplied to form the origination probability", which would give an origination probability for the flagellum of 10 _-1170. This is well below the universal probability bound, demonstrating, in his view, that the flagellum could not have evolved.

Dembski states that, given enough time, any event with a probability larger than 10_-150 might well take place. He puts the odds of evolving the 30 proteins of the bacterial flagellum at 20_-30 ("around 10_-39")  and explains that since the flagellum requires 30 such proteins, they "will all need to be multiplied to form the origination probability", which would give an origination probability for the flagellum of 10 _-1170. This is well below the universal probability bound, demonstrating, in his view, that the flagellum could not have evolved.

==References==

==References==

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[[category:biology]]

[[Category:Biology]]

[[Category:microbiology]]

[[Category:Microbiology]]