User:Fink.182/sandbox

Andrew Fink.182 Tues 11:30am 9/15/2014

Wikipedia Project Topic and 5 Primary References

The topic I want to use for my Wikipedia project is the question, “How did the vertebrate eye evolve?” I have always been fascinated with the complexity of the human eye and intrigued by the perceived flaws in its structure, such as the blind spot and the location of its photoreceptors. I can’t wait to learn about this complex organ and what modern science’s best understanding is of how the vertebrate eye came into existence. Some knowledge I want to gain through my research is the individual stages in the evolution of the vertebrate eye, the advantages to organisms that had this trait, and the estimated time span that it took for these changes to occur. Dan-E. Nilsson is a Swedish scientist who is a prominent researcher and contributor to the field of animal eye evolution. He has been the leading author on many important papers regarding the evolution of the animal eye and for this reason, he is either a lead author or contributing author to many of my primary references I plan to use. The list is as follows:

1.	Nilsson, D.-E., and S. Pelger. "A Pessimistic Estimate of the Time Required for an Eye to Evolve." Proceedings of the Royal Society B: Biological Sciences 256.1345 (1994): 53-58. Web.

-This paper discusses the individual proposed stages in the evolution of animal eyes and how quickly these stages may have taken place. The stages begin with a flat grouping of light-sensitive cells. These begin to move inward to form a cup-like structure that allows for better light detection, and then the opening of the eye structure shrinks for better focusing. Eventually the structure becomes spherical and a jelly-like fluid fills the inside, allowing for better light diffraction. Finally a lens is developed that allows for better focusing. All these steps are sequenced chronologically and a basic time line of less than 500,000 years is given for the complete evolution of the eye.

This paper will be very useful to me in terms of describing the development of the eye. I can reference the individual stages the paper describes, the advantages each has, and the timeline of the evolution.

2.	Schoenemann, Brigitte, Jian-Ni Liu, De-Gan Shu, Jian Han, and Zhi-Fei Zhang. "A Miniscule Optimized Visual System in the Lower Cambrian." Lethaia 42.3 (2009): 265-73. Web.

-This paper discusses the formation of the lens found in the lobopod Miraluolishania haikouensis and how even though this lens is costly, it was not a wasted step in the evolution of the eye. The eye of the lobopod is very small with a miniscule lens that does not offer much refractive power. However, the development of this lens still offered a unique evolutionary advantage to these organisms and it can represent a stage in the evolution of the vertebrate eye.

3.  Nilsson, Dan-E. "Eye Ancestry: Old Genes for New Eyes." Current Biology 6.1 (1996): 39-42. Web.

-This paper discusses the involvement of master control genes in animals for eye development. In the study of Drosophila, the Pax-6 gene was examined and it was found that when manipulated, eye development could take place almost anywhere on the organism’s body. Genes homologous to Pax-6 indicate that it is a master control gene in both vertebrates and insects.

I can use this paper to discuss the genetic portion of the evolution of the vertebrate eye and how regulation of homologous genes to Pax-6 can account for the tremendous diversity of eyes animals have today.

4. Nilsson, Dan-E. "Eye Evolution and Its Functional Basis." Visual Neuroscience 30.1-2 (2013): 5-20. Web.

-This paper discusses how more demanding behaviors in animals required the need for increased capabilities of their photoreceptor organs over the course of evolution. He proposes the different stages of nondirectional photoreception, low-resolution vision, and high-resolution vision, and also performs mathematical calculations that agree with these prominent stages in eye evolution.

I can use this information to discuss what selective pressures guided the development of the vertebrate eye and how the evolution of the eye and more-demanding behaviors in animals correlated with each other.

5. Nilsson, D.-E. "The Evolution of Eyes and Visually Guided Behaviour."Philosophical Transactions of the Royal Society B: Biological Sciences 364.1531 (2009): 2833-847. Web.

-This paper contains a wealth of knowledge that will be useful in my research. It discusses the different kinds of opsins and their associated pathways, the evolution of the eye at four different levels, and the properties of an animal’s sensory system and what demanding behaviors selected for them. It also discusses which definitive changes in the visual system accounted for the different stages of eye development.

I can use this information in combination with my other resources to build a better and more complete picture of the evolution of the vertebrate eye. It will complement my previous reference, yet add more insightful information in a different fashion. The images it contains also helps clarify information presented in other references.

Fink.182 (talk) 05:13, 15 September 2014 (UTC)

Wikipedia Assignment #2: October 1st, 2014

The following is the article on the Evolution of the Eye that I added suggestions to on how it could be improved, as well as a sentence and citation:

https://en.wikipedia.org/wiki/Evolution_of_the_eye

Three Suggestions:

1) History of Research needs to be renamed & updated

I agree with the previous post that this section has to be given a new title. The current one is very misleading to the reader, as there is no talk of historical research in that paragraph. It is simply the classic intelligent design vs evolution debate, and a new section should be created for this if we wish for it to be included. A possible title for it could be "Classic Source of Debate" or "Darwin's Impact".

I still think that we should include some aspect of research in this article, though. Perhaps a section titled "Modern Research" would be fitting. There is all sorts of modern research going that aims to discover different genes and mechanisms involved in the eye's evolution. One prominent author is Dan-E. Nilsson. Although his earlier works are much more famous, particularly his paper explaining the timeline for the evolution of the eye, there are several that have been published more recently. I think modern applications with any topic is a subject of curiosity for readers and would be a good addition.

2) Detail in "Rate of Evolution"

In this section, the first paragraph is good. However, the second one seems like it was added without much thought put in. The paper used as a reference (reference #7 in this Wiki article) has tons of detail in describing the evolution of the eye and I think a little more detail would be helpful. To begin, I will include what Nilsson's paper actually includes, which is the pessimistic approximation of 364,000 generations needed for the development of the camera eye. Also, the authors clearly state that the eye doesn't evolve on its own, independent of the organism. The actual number of generations needed for the eye to evolve in different species can we wide ranging, but their pessimistic estimate is the best we have. Feel free to add more content after me.

3) Imperfections in the vertebrate eye

The section titled "Evolutionary Baggage" is off to a good start, yet could use some improvements and added detail. It mentions the most common description of the way the photoreceptors are located behind many other cell layers, and how this is a result of evolution. Another main piece of baggage that is not mentioned is the blind spot, where the optic nerve exits the eye. Here are some links to a blog that was written by a physician named Steven Novella on the disadvantages that the vertebrate eye has due to its evolution:

http://theness.com/neurologicablog/index.php/the-not-so-intelligent-design-of-the-human-eye/

http://theness.com/neurologicablog/index.php/the-not-so-intelligent-design-of-the-human-eye-part-ii/

^^ These can be used to comprehensively cover the flaws the vertebrate eye has and how these are a consequence of evolution by natural selection.

Sentence & Citation:

After the photosensitive cell region invaginated, there came a point when reducing the width of the light opening became more efficient at increasing visual resolution than continued deepening of the cup.

Fink.182 (talk) 01:44, 1 October 2014 (UTC)

Draft: The Evolution of the Vertebrate Eye

The vertebrate eye is a very complex organ, with many different types of cells and components that influence its functionality. It gives organisms numerous advantages in their environments, including enhancing their survival due to the ability to respond to various types of light-specific stimuli. Because of its incredible complexity, the eye was a favorite target of criticism from Darwin opponents and Creationist supporters who claimed that an organ so complex could not have arisen simply due to chance. Darwin himself admitted that on first glance, the evolution of the eye by natural selection seemed “absurd in the highest possible degree”. However, he went on to say that if continuous improvements from a simple to more complex eye could be shown to exist and these changes were heritable, then the formation of the eye “should not be considered as subversive of the theory” (Darwin, 1859). Through the analysis of all existing evidence, modern theory has the evolution of the vertebrate eye occurring in 4 characteristic stages during which a simple group of photoreceptors evolved into the complex eye we know today.

The first stage in the evolution of the vertebrate eye was a period of nondirectional photoreception (Nilsson, 2013). The earliest photoreceptors were grouped in a circular patch, with a dark pigment epithelium surrounding them (Nilsson and Pelger, 1994). They were used by organisms simply for light detection, but lacked the capacity to generate any type of image due to their simplicity and the organism’s lack of a sufficient nervous system (Lamb et al, 2008). A number of important behaviors in organisms developed as a result of photoreceptors - aquatic animals used the light intensity to gauge their depth in the ocean, while other organisms used shadow detection to orient themselves to their environments and establish circadian rhythms (Nilsson, 2013). This type of light detection worked for these early animals and gave them an advantage over those without a visual system, but a new stage in the evolution of the eye allowed for more complex interactions with the environment and was heavily favored once it began to emerge.

The next stage in the evolution of the eye was directional photoreception, which allowed organisms to have spatial resolution and to locate the direction of a light stimulus (Nilsson, 2013). Two ways that directional photoreception was developed was through the invagination of the circular patch of photoreceptor cells and a constriction of the epithelial cells lining the opening where light entered. First, the photoreceptors developed into a pit because this was the most efficient way to increase the eye’s optical resolution. Cells closer to the opening of the structure received light stimuli before cells at the back, allowing for limited detection of space around them. After a while, however, continued deepening of the photoreceptor pit lost its effectiveness and gave way for the second kind of transformation - the formation of a pinhole. During this period, the epithelial cells lining the opening of the pit began to grow closer together and reduced the amount of light that could enter. Reducing the angle at which light can enter gave organisms the ability to identify direction, as photoreceptors on the right half of the pit could only respond to light entering from the left, and photoreceptors on the left half of the pit could only respond to light entering from the right (Nilsson and Pelger, 1994). As soon as directionality evolved, the organism could begin to compare its own movements to light stimuli in different directions, allowing it to orientate itself towards or away from light (Nilsson, 2009). Some of the more prominent advantages given to organisms with the ability to detect light directionality included the ability to both protect themselves from predators and catch their prey.

Another stage of eye evolution occurred that was even more advantageous than the preceding stage. This stage is called low-resolution vision, and is the first time that true eyes and vision were developed (Nilsson, 2013). Low-resolution vision involved the overgrowth of transparent cells over the eye opening, the filling of the newly-created chamber with a blob of mucus or jelly called the vitreous humor, and the formation of a crude crystalline lens in the eye. The layer of transparent cells over the opening of the eye prevented infection and allowed the humor to develop within the chamber. This allowed for light collection and the slight convergence of entering light (Schoenemann et al, 2009), setting the eye up for future lens formation to further direct light to one area.

In a lensless eye, a distant point of light enters and hits the back of the eye with the same size as when it entered. Adding a lens to the eye directs this incoming light onto a smaller surface area, without reducing the intensity of the stimulus (Nilsson and Pelger, 1994). Lenses can consist of a variety of materials and substances but in vertebrates, the lens is formed from a composition of proteins belonging to two families, the α-crystallins and the βγ-crystallins. Both were categories of proteins originally used for other functions in the organism, but eventually adapted for the sole purpose of vision in animal eyes. These crystallins are special because they have the unique characteristics required for transparency and function in the lens such as tight packing, resistance to crystallization, and extreme longevity, as they must survive for the entirety of the organism’s life (Slingsby et al, 2013). The development of a humor and lens in the vertebrate eye allowed for low-resolution vision in the organism and gave it environment-specific advantages that were selected for during the course of evolution. The organism could now control its speed and direction of locomotion, avoid objects in the environment, and find an adequate habitat (Nilsson, 2013).

The final stage in the evolution of the vertebrate eye is the development of high-resolution vision (Nilsson, 2013). This stage is overarching and encompasses many different developments in the eye, all which contribute to higher vision resolution. The most immediate development during this stage is the formation of a cornea, iris, and the aqueous humor in between these two structures. The cornea is the transparent layer at the front of the eye that covers the iris, pupil and anterior chamber of the eye, and the iris is the colored part of the eye that controls how much light enters. These are three key components of the vertebrate eye that allowed for increased visual resolution. The cornea protects the eyeball while at the same time accounting for approximately 2/3 of the eye’s total refractive power. Along with the lens and two humors, it is responsible for converging light and aiding the focusing of it on the back of the retina (Ali, 1985). Other developments in high-resolution vision include color vision, accommodation of the lens, and physical location of the eyes on the organism.

Compared to the other three stages of eye evolution, high-resolution vision allows for organisms to have high interaction and control of their environments, giving them advantages for both survival and reproduction. The ability to detect prey and predators is increased significantly over previous stages, mate recognition to reproduce is enhanced, and finding and securing food and suitable habitats is augmented (Nilsson, 2013). Many high level behaviors can only occur because of the evolution of high-resolution vision in the eye, such as reading this sentence and this paragraph of words.

Some evidence for the evolution of the vertebrate eye can be found in the fossil record. Close examination of the structure of eye orbits and openings in fossilized skull for blood vessels and nerves can lead to appropriate evolutionary conclusions (Young, 2008). The shared use of the Pax-6 gene in eye development among all vertebrates offers another form of evidence, implying that all eyes evolved from a common ancestor (Nilsson, 1996). All in all, the evolution of a circular patch of photoreceptor cells to a fully functional vertebrate eye has been approximated based on rates of natural selection and evolution, among other factors. Based on pessimistic calculations that consistently overestimate the time required for each stage and a generation time of one year, it has been proposed that it would take less than 364,000 years for the vertebrate eye to evolve from a patch of photoreceptors (Nilsson and Pelger, 1994). Considering that life on earth is billions of years old, this is a tiny blip over the course of evolution.

The evolution of the vertebrate eye took place in four major stages, moving from a simple patch of photoreceptor cells all the way to a fully functional, high-resolution visual organ for the organism. The process began with the invagination of the photoreceptor cells that resulted in the acquisition of slight depth perception. It then continued with the constriction of the eye hole that resulted in the ability to sense directionality of light. A transparent membrane covered the opening of the eye, allowing for low-resolution vision by the development of a lens and vitreous humor in the eye chamber. Finally, the cornea, iris, and aqueous humor developed that contributed to the modern, high-resolution vision of vertebrates. At each stage in the evolution, advantages were obtained that allowed organisms to have increased relative fitness, imposing selection for this new trait in future generations. Pessimistic calculations of the time required for the vertebrate eye to develop propose a time period that is proportionally insignificant over the course of evolution, allowing plenty of time for an organ as complex and amazing as the human eye to evolve. Although Darwin was at first concerned that the human eye could turn his theory inside out, current evidence suggests that he had nothing to worry about.

References

1) Ali, M.A. and M. A. Klyne. 1985. Vision in vertebrates. New York: Plenum Press.

2) Darwin, C. 1859. On the origin of species (1st edition). London: John Murray.

3) Lamb, T. D., E. N. Pugh, and S. P. Collin. 2008. The origin of the vertebrate eye. Evo Edu Outreach 1:415-426.

4) Nilsson, D.-E. 1996. Eye ancestry: old genes for new eyes. Current Biology 6:39-42.

5) Nilsson, D.-E. 2009. The evolution of eyes and visually guided behaviour. Philosophical Transactions of the Royal Society B: Biological Sciences 364:2833-2847.

6) Nilsson, D.-E. 2013. Eye evolution and its functional basis. Visual Neuroscience 30:5-20.

7) Nilsson, D.-E., and S. Pelger. 1994. A pessimistic estimate of the time required for an eye to evolve. Proceedings of the Royal Society B: Biological Sciences 256:53-58.

8) Schoenemann, B., J. Liu, D. Shu, J. Han, and Z. Zhang. 2009. A miniscule optimized visual system in the lower cambrian. Lethaia 42:265-73.

9) Slingsby, C., G. J. Wistow, and A. R. Clark. 2013. Evolution of crystallins for a role in the vertebrate eye lens. Protein Science 22:367-380.

10) Young, G. C. 2008. Early evolution of the vertebrate eye – fossil evidence. Evo Edu Outreach 1:427-438.

Fink.182 (talk) 05:23, 13 November 2014 (UTC)

Final: The Evolution of the Vertebrate Eye

The vertebrate eye is a very complex organ that contains many different types of cells and components that influence its functionality. It gives organisms numerous advantages in their environments over eye-less creatures, including enhancing their survival due to the ability to respond to various types of light-specific stimuli. Because of its incredible complexity, the eye was a favorite target of criticism from Darwin opponents and Creationist supporters who claimed that an organ so complex could not have arisen simply due to chance. Darwin himself admitted that on first glance, the evolution of the eye by natural selection seemed “absurd in the highest possible degree”. However, he went on to say that if continuous improvements from a simple to more complex eye could be shown to exist and these changes were heritable, then the formation of the eye “should not be considered as subversive of the theory” (Darwin, 1859). Through the analysis of existing evidence, modern theory has the evolution of the vertebrate eye occurring in four characteristic stages during which a simple group of photoreceptors evolved into the complex eye we know today.

The first stage in the evolution of the vertebrate eye was a period of nondirectional photoreception (Nilsson, 2013). The earliest photoreceptors were grouped in a flat, circular patch with a dark pigment epithelium surrounding them (Nilsson and Pelger, 1994). They were used by organisms simply for light detection, but lacked the capacity to generate any type of image or discern direction due to their simplicity and the organism’s lack of a sufficient nervous system (Lamb et al, 2008). A number of important behaviors in organisms developed as a result of photoreceptors - aquatic animals used the light intensity to gauge their depth in the ocean, while other organisms used shadow detection to orient themselves to their environments and establish circadian rhythms (Nilsson, 2013). This type of light detection worked for these early animals and gave them an advantage over those without a visual system, but a new stage in the evolution of the eye allowed for more complex interactions with the environment and was heavily favored once it began to emerge.

The next stage in the evolution of the eye was directional photoreception, which allowed organisms to have spatial resolution and to locate the direction of a light stimulus (Nilsson, 2013). Two ways that directional photoreception developed was through the invagination of the flat patch of photoreceptor cells and a constriction of the epithelial cells lining the opening where light entered. First, the photoreceptors developed into a pit because this was the most efficient way to increase the eye’s optical resolution. Cells closer to the opening of the structure received light stimuli before cells at the back, allowing for limited detection of depth and space around them. After a while, however, continued deepening of the photoreceptor pit lost its effectiveness and gave way for the second kind of transformation - the formation of an eye pinhole. During this period, the epithelial cells lining the opening of the pit began to grow closer together and reduced the amount of light that could enter. Reducing the angle at which light can enter gave organisms the ability to identify direction, as photoreceptors on the right half of the pit could only respond to light entering from the left, and photoreceptors on the left half of the pit could only respond to light entering from the right (Nilsson and Pelger, 1994). As soon as directionality evolved, the organism could begin to compare its own movements to light stimuli in different directions, allowing it to orientate itself towards or away from light (Nilsson, 2009). Some of the more prominent advantages given to organisms with the ability to detect light directionality included the ability to navigate their environment better, protect themselves from predators and catch prey more effectively.

Another stage of eye evolution occurred that was even more advantageous than the preceding stage. This stage is called low-resolution vision, and is the first time that true eyes and vision were developed (Nilsson, 2013). Low-resolution vision involved the overgrowth of transparent cells over the eye opening, the filling of the newly-created chamber with a blob of mucus or jelly called the vitreous humor, and the formation of a crude crystalline lens in the eye. The layer of transparent cells over the opening of the eye prevented infection and allowed the humor to develop within the chamber. This allowed for light collection and the slight convergence of entering light (Schoenemann et al, 2009), setting the eye up for future lens formation to further direct light to one area.

In a lensless eye, a distant point of light enters and hits the back of the eye with about the same size as when it entered. Adding a lens to the eye directs this incoming light onto a smaller surface area, without reducing the intensity of the stimulus (Nilsson and Pelger, 1994). Lenses can consist of a variety of materials and substances but in vertebrates, the lens is formed from a composition of proteins belonging to two families, the α-crystallins and the βγ-crystallins. Both were categories of proteins originally used for other functions in organisms, but eventually were adapted for the sole purpose of vision in animal eyes. These crystallins are special because they have the unique characteristics required for transparency and function in the lens such as tight packing, resistance to crystallization, and extreme longevity, as they must survive for the entirety of the organism’s life (Slingsby et al, 2013). The development of a humor and lens in the vertebrate eye allowed for low-resolution vision in the organism and gave it environment-specific advantages that were selected for during the course of evolution. The organism could now control its speed and direction of locomotion, avoid objects in the environment, and find an adequate habitat (Nilsson, 2013).

The final stage in the evolution of the vertebrate eye is the development of high-resolution vision (Nilsson, 2013). This stage is overarching and encompasses many different developments in the eye, all which contribute to higher vision resolution. The most immediate development during this stage is the formation of a cornea, iris, and the aqueous humor in between these two structures. The cornea is the transparent layer at the front of the eye that covers the iris, pupil and anterior chamber of the eye, and the iris is the colored part of the eye that controls how much light enters. These are three key components of the vertebrate eye that allowed for increased visual resolution. The cornea protects the eyeball while at the same time accounting for approximately 2/3 of the eye’s total refractive power. Along with the lens and two humors, it is responsible for converging light and aiding the focusing of it on the back of the retina (Ali, 1985). Other developments in high-resolution vision include color vision, accommodation of the lens, and physical location of the eyes on the organism.

Compared to the other three stages of eye evolution, high-resolution vision allows for organisms to have high interaction and control of their environments, giving them advantages for both survival and reproduction. The ability to detect prey and predators is increased significantly over previous stages, mate recognition to reproduce is enhanced, and finding and securing food and suitable habitats is augmented (Nilsson, 2013). Many high level behaviors can only occur because of the evolution of high-resolution vision in the eye, such as reading this sentence and learning complex behaviors from other organisms.

Some evidence for the evolution of the vertebrate eye can be found in the fossil record. Close examination of the structure of eye orbits and openings in fossilized skull for blood vessels and nerves can lead to appropriate evolutionary conclusions when compared to fossils of different time periods (Young, 2008). The shared use of the Pax-6 gene in eye development among all vertebrates offers another form of evidence, implying that all eyes evolved from a common ancestor (Nilsson, 1996).

The evolution of a circular patch of photoreceptor cells into a fully functional vertebrate eye has been approximated based on rates of mutation, relative advantage to the organism, and natural selection. Based on pessimistic calculations that consistently overestimate the time required for each stage and a generation time of one year, which is common in small animals, it has been proposed that it would take less than 364,000 years for the vertebrate eye to evolve from a patch of photoreceptors (Nilsson and Pelger, 1994). Considering that life on earth is billions of years old, this is a tiny blip over the course of evolution.

The evolution of the vertebrate eye took place in four major stages, moving from a simple patch of photoreceptor cells all the way to a fully functional, high-resolution visual organ for the organism. The process began with the invagination of the photoreceptor cells that resulted in the acquisition of slight depth perception. It then continued with the constriction of the eye pinhole that resulted in the ability to sense directionality of light. A transparent membrane covered the opening of the eye, allowing for low-resolution vision by the development of a lens and vitreous humor in the eye chamber. Finally, the cornea, iris, and aqueous humor developed that contributed to the modern, high-resolution vision of vertebrates. At each stage in the evolution, advantages were obtained that allowed organisms to have increased relative fitness, imposing positive selection for this new trait in future generations. Pessimistic calculations of the time required for the vertebrate eye to develop propose a time period that is proportionally insignificant over the course of evolution, allowing plenty of time for an organ as complex and amazing as the human eye to evolve. Although Darwin was at first concerned that the human eye could turn his theory inside out, current evidence suggests that he had nothing to worry about.

References

1.	Ali, M.A. and M. A. Klyne. 1985. Vision in vertebrates. New York: Plenum Press.

2.	Darwin, C. 1859. On the origin of species (1st edition). London: John Murray.

3.	Lamb, T. D., E. N. Pugh, and S. P. Collin. 2008. The origin of the vertebrate eye. Evo Edu Outreach 1:415-426.

4.	Nilsson, D.-E. 1996. Eye ancestry: old genes for new eyes. Current Biology 6:39-42.

5.	Nilsson, D.-E. 2009. The evolution of eyes and visually guided behaviour. Philosophical Transactions of the Royal Society B: Biological Sciences 364:2833-2847.

6.	Nilsson, D.-E. 2013. Eye evolution and its functional basis. Visual Neuroscience 30:5-20.

7.	Nilsson, D.-E., and S. Pelger. 1994. A pessimistic estimate of the time required for an eye to evolve. Proceedings of the Royal Society B: Biological Sciences 256:53-58.

8.	Schoenemann, B., J. Liu, D. Shu, J. Han, and Z. Zhang. 2009. A miniscule optimized visual system in the lower cambrian. Lethaia 42:265-73.

9.	Slingsby, C., G. J. Wistow, and A. R. Clark. 2013. Evolution of crystallins for a role in the vertebrate eye lens. Protein Science 22:367-380.

10.	Young, G. C. 2008. Early evolution of the vertebrate eye – fossil evidence. Evo Edu Outreach 1:427-438.

Fink.182 (talk) 05:49, 14 November 2014 (UTC)

Wikipedia Article Edits: https://en.wikipedia.org/wiki/Evolution_of_the_eye

History of Research

-Modern researchers have been putting forth work on the topic. D.E. Nilsson has independently put fourth four theorized general stages in the evolution of a vertebrate eye from a patch of photoreceptors. . Nilsson and S. Pelger published a classical paper theorizing how many generations are needed to evolve a complex eye in vertebrates. . Another researcher, G.C. Young, has used fossil evidence to infer evolutionary conclusions, based on the structure of eye orbits and openings in fossilized skulls for blood vessels and nerves to go through. . All this evidence adds to the growing amount of evidence that supports Darwin's theory.

Rate of Evolution

-The evolution of a circular patch of photoreceptor cells into a fully functional vertebrate eye has been approximated based on rates of mutation, relative advantage to the organism, and natural selection. Based on pessimistic calculations that consistently overestimate the time required for each stage and a generation time of one year, which is common in small animals, it has been proposed that it would take less than 364,000 years for the vertebrate eye to evolve from a patch of photoreceptors.

Early Eyes

-Along with the lens and two humors, the cornea is responsible for converging light and aiding the focusing of it on the back of the retina. The cornea protects the eyeball while at the same time accounting for approximately 2/3 of the eye’s total refractive power. .

Lens Formation and Diversification

-In a lensless eye, a distant point of light enters and hits the back of the eye with about the same size as when it entered. Adding a lens to the eye directs this incoming light onto a smaller surface area, without reducing the intensity of the stimulus. .

-These crystallins belong to two major families, the α-crystallins and the βγ-crystallins. Both were categories of proteins originally used for other functions in organisms, but eventually were adapted for the sole purpose of vision in animal eyes. .

-These crystallins are special because they have the unique characteristics required for transparency and function in the lens such as tight packing, resistance to crystallization, and extreme longevity, as they must survive for the entirety of the organism’s life. .

Fink.182 (talk) 04:07, 18 November 2014 (UTC)