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Evolution of an eye in the savannah

FEW weeks ago we covered about the efficiency of zebras eyes, by doing that the topic created a room for us to have a closer look on how the eyes functions in the savannah where almost there is nowhere to hide when you are targeting a prey or saving your life from predators. 

Some scientific researches indicate that the first animal to evolve with what may be called an ancient eye appeared about 600 million years ago, but through genetic features researchers have discovered that the real eye among vertebrates evolved about 540 million years ago.

Through the use of fossils records scientists estimate the first animal carrying an eye evolved more than 540 million years ago. When the world was dominated by creatures with exoskeletons, different researches indicate that the first eyed animals had light sensitive mechanism which depended on photoreceptors cell which originated from their ancestors which had very weak brain that was being controlled by other parts of their bodies. Fossils records indicates that evolution of an eyes took good stage about 525 million years ago when the first ancestors of vertebrate animals evolved into the earth. 

These were mysterious creatures which had a well defined head and tail that enabled the balance of their bodies as they moved from one point to another on the world which was going through different geological and weather changes. These earlier vertebrate animals had no jaws to survival they were forced to dwell very close to the sea where it was possible to capture prey with soft bodies. During that time it was ancient predators that evolved with powerful vision which helped them to chase and capture their prey in a difficult about 485.4 million years ago when the planet was still recovering from an earlier weather which was dominated by falling of snow from the sky. 

With structure that can be divided into three main layers, scientists say mammalian eye can also be further divided into two main segments the anterior segment and the posterior segment but from those days to modern time, mammals normally have a pair of eyes although mammalian vision is not as excellent as bird vision, the structure of the mammalian eye owes itself completely to the task of focusing light onto the retina, this light causes chemical changes in the photosensitive cells of the retina, the products of which trigger nerve impulses which travel to the brain of a mammal such as an elephant. 

Among animals of the savannah, elephants have limited mobility of the eyes but different researches indicated that they can see well in dim light but not in bright light, scientists say the weakness happens because their eye contains very few photoreceptors and they cannot see very well further than 10 meters but some time they are able to see even from 20 meters when they venture into shade of tropical savannah. 

Different researches have indicated that the visual ability of elephants is limited because of the location of their eyes, ear and trunk which limits the limited mobility of the eye, this problem made ancestors of modern elephants to leave aquatic environment and migrate into savannah tropical forest from about 3.5 million years ago, today the African bush elephant is found in dry savannah area such as Mkomazi, Tarangire and Ruaha while its relative the African forest elephant prefer forest vegetations of equatorial area. 

History show that transformation of the landscape in East Africa about 5 million years ago came with changes of weather which impacted kind of vegetations which thrived in this part of the world but together with other factors it enabled the evolution of the first generation of lions between 1 million and 8 hundred thousand years ago. 

By using their eyes, from Africa these lions migrated to Europe about 7 hundred thousand years ago but when they attempted to habitat highlands in the central part of Eurasia weather forced them out about 3 hundred thousand years ago, they marched for a very long time until 21 thousand years ago when they arrived in Indian sub continent. 

That was long period which the world experienced different weather patens which were influenced by El Niño with trade winds in the south Pacific which affected this part of the world by bringing warm water to the Indian Ocean through western Pacific. 

That was a period which was characterized by different features including a huge blanket of dusty cloud which prevent Sun-rays to reach the ground. This made little difference between day time and night hours but it enable the first generation of lions to acquire special mechanism for night vision. 

Scientists say lions are mammals that have eyes which work at the same level like human eyes during day light but at night these apex predators see eight times more than human beings. Mainly lions see in blue and greens environment with highly developed night vision, this doesn’t mean they can see in the dark because if they walk and work on a black pitch they will be blind. 

Lion’s eyes are designed to work effectively in darkness where they are able to pick and use very little light available even from stars and moon, they have more rod cells than cone cells in the retina of their eyes, these are photoreceptor or light sensitive cells, and function to convert visible electromagnetic radiations or light into signals which stimulate biological process. 

Lion’s eyes are equipped with two photoreceptor cells which are rods and cones, each of these cells contributing information used by the visual system to form a representation of the visual activities. 

Cones cells are wider which work as colour detector while rods cells are narrow and they are responsible for light as they are distributed differently across the retina. 

This shows that lions have more light sensitive cells packed tightly in the fovea which is the most sensitive area of the retina, this means their eyes need little amount of light to see something in the darkness than human eyes. 

Lions have what is known as Tapetum lucidum, this is a reflective layer of cells positioned behind the retina. This means that light entering into the lions eye’s will be absorbed by either the rod or cone cells, light that passes through the retina and the photoreceptor cells is reflected back by the Tapitum lucidum while the light sensitive cells have a second chance to absorb the light waves, in effect doubling the effectiveness of their night vision. 

Furthermore, a lion’s eyes do not glow in darkness, but they contain a special reflective coating that will reflect even from moonlight due to the big size of their eyes. This reflective layer results in the eerie or eye shine which is seen when a light shine on lion’s eyes at night. 

Outside each eye of lions, there white patches which are located under each eye and work to enhance a little amount of light available while enabling the super predator to work effectively at night. 

History tells us that about 66 million years ago in a period called Jurassic which lasted for about 135 millions years the World was dominated by largest terrestrial vertebrate called Dinosaurs, changes in weather sent these giants into extinction and opened the world for other creature like gerenuk to evolve. 

The beautiful antelope did not came around with a huge body like elephant or powerful jaws and sharp claws of lions, it evolved with long neck and sharp eyes which are surrounded by white fur which send light into the eyes for a reasonable night vision. 

History shows that the modern eyes for vertebrate animals took more than 360,000 as passing through one stage to another in a long and complex process of evolution which included the development of photoreceptors, these were new kind of proteins that helped our ancestors to sense light through an ambient brightness that they were able to distinguish light from dark. 

Different fossil records show that with this visual development at that stage ancestor of vertebrates were unable to see things clearly, they were not able to distinguish shape, determine distance and direction of a moving body because they lacked an eyespot which works to allow the organism to move in response to light. 

In those days the photoreceptors of an eye had to go through a long process of evolution which involved between 40 to 65 different stages to gain a basic sense of direction together with the ability of managing the intensity of light, although until that stage the eyes of an ancient vertebrate animal was unable distinguish an object from its surrounding. 

In a process that benefited more than 96 percent of all living animals. The ancestors of modern vertebrate had to pass through multiple changes that included the shape and size of their eyes. Fossil records indicate that during those days animals carried flat eyes that were unable determine the direction of light. 

Geologists and historians say the evolution did not happened overnight, from about 541 million years ago for about 20 to 25 million years the development of an eye went through crucial stages which enabled the improvement of image processing and detection of light because the ancient aye lacked a lens, this means that a lensless eye was unable to process light produced by distant located object, about 419 million years ago some vertebrates started to develop ability of detecting colour, focus mechanism and location detection. 

Scientists believe that from that from about 164 million years ago a true or crown mammal evolved in a semi aquatic environment where it managed to acquire colour vision with high ability to differentiate red and green after some developments happened in the cones of their retinas.. 

Last Sunday, January 12th, 2019; was ...

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Author: REGINALD STANISLAUS MATILYA

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