Sunday, April 12, 2009
"Irreducible Complexity"
Carroll constantly talks about how evolution is derived from an accumulation of different mutations that singularly are only small variations through mutations that create a trait in an organism. But can Evolutionary Development explain every single happening in evolutionary history? One of the main arguments for intelligent design is the example of the motor like flagellum that developed in organisms in early earth history through the idea that the flagellum is a “irreducible complexity” and cannot be explained through Darwinian evolution. An “irreducible complexity” is defined as ". . . a single system composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning" (Behe, M. 1996a. Darwin's Black Box. New York: The Free Press). What are some other examples of structures in organisms that are “irreducible complexities” and what are some of the explanations of these examples? Can Evo Devo be used to explain the structure of the flagellum?
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Scientists have found that the development of the motor-like flagella can in fact be explained by evolutionary development, thus disproving Behe’s theory of irreducible complexity. They have found that the body of the flagella is similar to a needle like structure that certain pathogenic bacteria use to inject toxins called the Type Three Secretory System. While it is very similar to the flagella, it lacks 40 of the proteins necessary for proper flagella functioning. This conclusion disproves Behe’s definition of irreducible complexity because in this case, the removal of 40 proteins doesn’t cause the system to cease functioning, but rather, to have a different function. His definition of irreducible complexity ignores the fact that successive mutations can create various different structures with entirely different functions, while still evolving into a complex structure like the flagella.
ReplyDeleteAnother example disproving Behe’s theory is the blood clotting cascade. One of the clotting factors that Behe listed as a part of the clotting cascade was later found to be absent in whales, demonstrating that it is not essential for a clotting system to function properly. Also, jawless fish perform blood clotting with just six of the ten proteins that Behe listed as crucial to the functioning of the blood clotting cascade. He fails to recognize that there are examples of organisms with reduced versions of seemingly complex systems and that their presence suggests an evolutionary development of the structure.
Behe also argued that the eye is the perfect example of an irreducible complexity, due to its many elaborate and interlocking parts, seemingly all dependent upon one another. However, many scientist believe that eyes originated as very simple areas of photoreceptor cells used in the presence or lack of light. Later, organism’s developed a small depression for the photoreceptor cells in order to understand the light’s source. Even further in evolutionary development, this depression was deepened so that light would strike certain photoreceptor cells at certain angles, providing the organism with increasingly precise visual information. The aperture of the eye was then made smaller allowing organisms to make out faint shapes; this stage in the evolutionary development of the eye can be viewed in the nautilus. Finally, the outermost layer of cells became differentiated into a lens. Modern biologists recognize that the eye, an often cited example by intelligent design and creationism advocates, can actually be broken down into simpler structures and can indeed be explained by evolutionary development.
http://www.toarchive.org/faqs/behe.html
ReplyDeletehttp://en.wikipedia.org/wiki/Irreducible_complexity
One example of an IC complex lies within the Venus’ flytrap, Dionaea muscipula, which traps and digests insects to make up for the lack of N in the soil that surrounds its habitat. The “parts” of the Venus flytrap involve the trigger hairs and the lobes. In order to determine if an IC system exists, the function of the parts must be identified. The two lobes, the hinge between them (the midrib or the anchor), the trigger hairs, and spines which project from the edges of the lobes all make up the entire trap. The system consists of only these parts, and the trap needs every one of these parts for it to function (hence an IC system).
ReplyDeleteIn order to discern how the plant may have evolved into an IC complex, we look at the related plant called a Sundews or Drosera. These plants also trap insects using “flypaper” traps, which stick to the insects. This two has several parts, the glands on the center, the marginal tentacles, and the fluid/milk solution (consisting of nitrate and ammonia). The action of the bug on the surface of the tentacles first bends them towards the insect, which then causes the outside tentacles to enfold over the insect. This system too, consists of only these parts and in order for it to work successfully, all of them need to be present for function.
However, when the two plants are compared to each other, we see a problem with the argument that IC can’t evolve. The Venus flytraps lost the “glue” that the Sundews use, meaning that the lost a part rather than gaining a part, and were still capable of functioning. Due to evolution, a “snap trap” evolved within the Venus flytrap to overcompensate for the fact that the “sticky solution was lost”, avoiding the argument that IC can’t evolve.
http://www.talkorigins.org/faqs/behe.html
ReplyDeleteThere are many examples of Irreducible complexities. One example of an IC is Cilia. Cilia are hair-like structures; they are used by plants and animals to transport water and other fluids across many different surfaces. A prime example would be ourselves and how mucus sweeps our throat to get rid of any contaminants and foreign particles. Cilia are also used by single-celled organisms for transport through water. Cilia are very different in that they have their own ways of moving and bending. The mechanism contains microtubules, which are rod-like structures that are in a ring shape. Microtubules are components of the cytoskeleton composed of hollow cylindrical rods, 25 nm in diameter, formed of 13 rows of solid tubulin protofilaments that run parallel to the microtubule long axis. Adjacent microtubules are connected to each other by two types of bridges-a flexible linker bridge and an arm that can walk up the neighboring microtubule. The cilia bends by activating the walker arms, and the sliding motion that this tends to generate is converted to a bending motion by the flexible linker bridges.
ReplyDeleteThe cilium has a lot of components such as, microtubules, linker bridges, and walker arms. These 3 components form what is required for functionality. For without one of these components, the system will not function. The cilium cannot function with the microtubules alone because microtubules are too rigid and strict to move around. Even if you add the flexor bridges, the cilia would still not be able to function because there is no motor, which are walker muscles, and the cilia will not bend. If we have microtubules and the walker arms but no flexible linker arms, the microtubules will keep on sliding past each other till they float away from each other and are lost. So, in conclusion the cilia need all three parts to function and cilia is a classical definition of IC because all parts are needed. The cilia tends to be an argument that Michael Behe makes in that it could not have occurred naturally, because it is simply too complex to function because as Darwinism has no mechanism for adding all the components at once. Darwin's is of gradual mutations which lead to the benefit of the organism. If just one of these components occurred then the cilia would not function and it would not be beneficial to the organism. Then there would be no need for it then. This is the debate that Behe is trying to make.
http://www.arn.org/docs/behe/mb_mm92496.htm
http://www.intelligent-design-evidence.com/irredcomplexity.html
en.wiktionary.org/wiki/microtubule
http://books.google.com/books?id=rP7wV9S1EsYC&pg=PA408&lpg=PA408&dq=cilia+irreducible+complexity&source=bl&ots=njx0Dv7rG3&sig=H4svs4oDLp1iwFZ9ZXDGdLk8QgU&hl=en&ei=XEDlSZWsG5TsnQe6tYS1CQ&sa=X&oi=book_result&ct=result&resnum=10
Michael Behe, the creator and coined the term irreducible complexity states that, some biological designs were too complex to have evolved from simpler and less complete predecessors. Behe also states that the removal of any parts that are irreducible complex would cause the entire structure to break and never regain functionability. In the book it states that Behe has said that flagellum are irreducibly complex, however there is evidence that disproves it. Flagellum is a tail like structure on the end of a cell that aids in the movement. It usually works like a motor in a whip like fashion to propel a cell forward or backwards. To refute the idea of Behe, PBS/Nova found a logical and possible origin of the flagellum. A three type syringe system used by bacteria to inject toxins into other cells shows the making and basic structure that with specialization and modernization would create a flagellum. This however still has one leak, the locomotion process for a cell to recognize how to control the flagella and move it. In further research it shows that process to remove the syringe like thing of the bacteria from the infected cell, it must have needed a whip like movement to remove it. This could have been the basis and the bacteria could start to use it as ancestral flagella for movement, and then with time and chance create full components of the flagellum system. This could be seen by the bacteria that caused the bubonic plague. Under a microscope some bacteria use their needlelike injections to help propel them forward for locomotion. This could be the possible solution for the evolution of flagellum, however, nobody will ever know and this can be his best hypothesis one can generate.
ReplyDeleteThe human eye is one of the greatest evolutionary feats. It creates the ability to see a trichromatic full color vision that has progresses primate and human ability above all. It has made it one of the most important things, and humans rely on it so much because it is so effective. Evolutionary history has showed that the full color eye is so useful that the need for advanced smell and hearing has diminished because the eye can do so much more. The reason it is put under irreducible complexity is because of its so many interlocking parts that must be together to get the best function possible. Behe has conceded that the origins of the large parts of the eye have been proven to evolve, and believes that it could work. However, he believes that the light sensitivity at the molecular level and all the reactions that go through the process to make it work defy evolution, and therefore have no explanation how it works. The start of the eye came to be from ancient photoreceptors that helped bacteria sense a presence of light or not, but not a direction. Slowly over time as depressions happened in the photoreceptor cells to create a better sense of light direction and better sense to obtain a certain vision of the object. Then as the pit got deeper, light would strike certain cells in certain angles that would help refine the image and make it more functional. Since the hole that light filtered through was so small, it made it like a pinhole camera, and it already had focused light strike certain things and get a quick recognition and make dim shapes. Afterwards, the eye had to be covered up by a transparent lens to focus the light more, and more advanced eye cells had to develop as a result in the retina to help focus and send the message to the brain. This is the accepted idea that is believed to have happened over the Cambrian period. Then for the human eye more specialized needs must have emerged in primates to dictate for light separation to make it possible to see full color eyes. This is the method stated by Darwin, and many believe this to be true. They believe this because every stage proposed by Darwin was actually proved to be true at some time, and this leads to show that random mutation that was selectively advantageous to the organism has came about to create the eye. Another way to disprove the theory of the human eyes is that it’s not perfect. If it was created by something it would have a much better design. It’s true that humans have full color vision, but the eye structure was designed that other species could have better eyesight. Blood vessels run across the surface of the retina instead of beneath it, which means if one pops or leaks, it could lead to blurred vision. There is proof a better eye design in squids which have blood vessels underneath the retina, however they are not able to see in full color. This shows that the eye must have evolved because there are so many different types and the human eye is not perfect so it could get better to be an even better selective advantage and is reducible.
http://www.pbs.org/wgbh/evolution/library/01/1/l_011_01.html
http://en.wikipedia.org/wiki/Irreducible_complexity