Why eye pigmentation is or is not an adaptation. 

Why Eye pigmentation is or is not an adaptation.

There are different environments that the different parts of the world offer. Some of the are favourable for human and other life existence while some others are harsh and unfriendly. It is, however, essential that life is distributed in all areas. Asa result, the different climatic and environmental factors make life in the different. Fitting into different climate regions based on finding a means to avoid the adverse effects of the environment is called adaptation. Some of the traits that have been associated with adjustment include the development of webbed feet, claws and behavioural adaptations of animals. The changes take longer to occur, and the adaptations may take generations to form after exposure to the new environments. Some of the variations that the humans living in different areas all around the world include eye and skin pigmentation. This paper is a discussion of why the eye pigmentation is or is not an adaptation.

It is notable that the eyes of different people all over the world have different colours such as blue, brown or green.  The colour of the eyes is most determined by the iris. It contains colours that range from amber, blue, brown, grey, green, hazel and red. The most common eye colour is brown and the rarest being green. Several factors determine the colour of the eyes. One of them is the amount of melanin that is produced by the individual. The pigment is produced to determine the colour of the skin, eyes and hair. People who are dark have more melanin produced in their bodies, and vice versa is also correct. The pigment is produced by cells called melanocytes.  The pigment is an adaptation for protecting the skin against harmful Ultraviolet Rays, as explained below.

The people who live in areas that are associated with the areas of high sunlight concentrationare likely to be affected negatively by the sun rays. Melanin concentration is seen to range from the very dark (typical in Africa) to yellowish or ink which is common in Northern Europe.  The ones in the tropical regions produce more melanin to keep out the sun rays that they are exposed to in their environment. The fact above does not mean that the people in Northern Europe do not produce melanin. There are two types of melanin that are produced; pheomelanin and eumelanin. Eumelanin is brown and black while pheomelanin is yellowish or pinkish. The people in  Africa, therefore, produce eumelanin and those in Northern Europe produce pheomelanin. The effect of melanin on eye colour is explained below.

Brown is one of the most common eye colours all over the world, with 55% to 79% of all the people having such characteristics. They contain the most melanin, and they are adaptive to helping to avoid direct sunlight from reaching the human eyes. Blue eye is common in Europe, and 8% of the people have them worldwide. Hazel is uncommon with 5% and is common in Europe and the United States.  The other colours, such as Gray and amber, are also exhibited in small percentages of people.

According to the theory of adaptation and evolution, all the people had a similar brown colour since they all needed to avoid the harsh tropical climates. Their eyes were, therefore, more brown since the melanin produced was in large quantities.  Scientists believed that the people lived in climates that were hot all year round and the brown colour was a good adaptation for them. It was also common to see the dark Irises in most people. As they moved further north and south, the rays of the sun were weaker. The amount of Ultraviolet radiation in such areas reduced significantly. The result was that the people no longer needed protection from the rays. The eye colour, therefore, got adapted to the conditions and the eye colour became lighter over generations. The lightening also made it easy for them to see in the cold and relatively darker winters compared to the environment that they had previously been used to. Based on the above explanation, eye colour is an adaptation.

Several genes are involved in eye colour. The main gene involved in this process is  OCA2. It is a gene that leads to the production of P-Protein. It is also called the melanocyte-specific transporter protein. It is involved in the transport of tyrosine which is the precursor form of melanin. Its main function is to ensure that the production of the melanin compound in hu7mans. It is different, as seen above, since different people have different types of melanin.  If the melanin is produced in large quantities in the Iris Stroma (upper layer of the iris), it leads to the development of brown eye colour. The lesser it is, the lesser the colour in the eyes. In some cases, the strain is too little that it leads to the formation of grey colour. In some people, especially in Russia, the colour is very minimal, and their eyes even show some reddish colour.

The OCA2 gene is not similar in all the people. It varies, and so does the type of melanin produced. The melanin is a biopolymer molecule. It is produced in a layer under the skin in cells known as melanosomes and transported to the eyes skin and hair by thin cellular projections. As different people breed with each other, the alterations of genes happen, and the results differ from one person to another. It is evident in the way some people have black hair but blue eyes. The paragraphs below will assess the different combinations of phenotypes and the effect that they have on eye colour.

The blue colour gene is recessive. A recessive gene is one whose characteristics can be hidden by the dominant gene.  The brown colour gene is dominant meaning that its phenotype can overrun that of a recessive gene. Genes come in pairs, and the interaction between the parent’s pairs of genes leads to different effects. When both parents have blue eyes,  the child will have blue eyes. This is because there is no dominant gene to mask the effects of the blue eye genes. In the case, there is only one expected result wich s babies wh have blue eyes. If one of the parents has a dominant gene for brown eyes in pairs the result will be ½ possibility of getting brown-eyed children. This is because the blue-eyed gene will be suppressed by the brown eyes, one which will consist of half of the children’s pair of the gene. The other half will be blue since te cross leads to pure blue genes in their systems.

In a case when one parent has a pair of genes that are for brown eyes and the other has one gene for brown eyes, the result is that the possibility of getting children will have brown eyes. Of the ¾ possibility, ¼ will have a pair that is purely brown genes, and ½ will have mixed genes for blue and brown. The brown gene will, however, show in the phenotype since it is dominant.  ¼ of the children will have blue eyes since the cross leads to pure blue eye genes. In a case when one parent has pure brown eye genes, and the other has purely blue eye genes, the possibility of getting children with brown eyes is 1. This is because all of the children will have mixed blue and brown genes, but the blue gene will be masked.

Basing on the above explanation, one can relate to the population of the world of people with brown eyes. Being a dominant gene, it is displayed more often compared to the blue eyes gene. The crosses of the people with the dominant and recessive genes also mean that the more people are likely to show the gene characteristics. This is the main reason why there are very many people who have a brown colour. In Europe, there are very many eye colour variations. Since the people there are all exposed to the same climatic and environmental conditions, it is wrong to conclude that the brown gene is a result of the adaptations to that environment. If it were so, almost all the population in the regions with little sunlight penetration would exhibit blue eye colour. It would also be evident that as one moves towards the north pole, the eyes of people would lighten up as one moves further from the equator.  This claim is, however, not true.

There are very many factors that affect the eye colour of people. It is irrational to conclude that it is due to adaptation as expressed above. In some cases, people seem to alter their eye colour depending on the light that they are exposed to. This is due to the different pigmentation of the two layers of the iris. If the two layers have different colours, there is a high chance that the light will be scattered differently in different levels of light.

In conclusion, the eyes of different people all over the world have different colours such as blue, brown or green.  Several factors determine the colour of the eyes. One of them is the amount of melanin that is produced by the individual. The pigment is produced to determine the colour of the skin, eyes and hair. Dark people have more melanin produced in their bodies, and vice versa is also correct. The people who live in areas that are associated with the areas of high sunlight concentration are likely to be affected negatively by the sun rays. The ones in the tropical regions produce more melanin to keep out the sun rays that they are exposed to in their environment.The people in  Africa, therefore, produce eumelanin and those in Northern Europe produce pheomelanin. Brown is one of the most common eye colours all over the world, with 55% to 79% of all the people having such characteristics. They contain the most melanin, and they are adaptive to helping to avoid direct sunlight from reaching the human eyes. Scientists believed that the people lived in climates that were hot all year round and the brown colour was a good adaptation for them. It was also common to see the dark Irises in most people. As they moved further north and south, the rays of the sun were weaker.The result was that the people no longer needed protection from the rays. The eye colour, therefore, got adapted to the conditions and the eye colour became lighter over generations.Being a dominant gene, it is displayed more often compared to the blue eyes gene. The crosses of the people with the dominant and recessive genes also mean that the more people are likely to show the gene characteristics. This is the main reason why there are very many people who have a brown colour. In Europe, there are very many eye colour variations. Since the people there are all exposed to the same climatic and environmental conditions, it is wrong to conclude that the brown gene is a result of the adaptations to that environment. There are very many factors that affect the eye colour of people. It is irrational to conclude that it is due to adaptation as expressed above.

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