From Bacteria to a Human Being: Secrets of Human Eye's Evolution

The human eye is a unique complicated mechanism. There has been a plethora of uncertainties and questions on how the human eye evolved to be so complex. Let's look deeper into the issue.

The evolution of human eyes is extremely complex, and it has been known that this complexity arose from the process of natural selection over the millions of years. It may sound unbelievable, but every next generation of humanity possesses slightly altered eyes with more precise mechanism of observing the world and slight general improvement. This peculiarity gives humans a decisive advantage over other species.

About six hundred million years ago, bacteria started developing some sort of eyes. Certain mutation processes gave some bacteria light-sensitive sensor system to perceive the surrounding world and adapt to light conditions. This phenomenon was described in the scientific literature as 'early eye'. These early eyes possessed a certain number of photoreceptors with light-sensitive cells known as opsins.

How do photoreceptors function? Opsins lie on the surface of photoreceptors to catch the picture from the surrounding reality. When chemical reaction happens, photoreceptors send an electrical signal towards the brain. According to neuroscience discoveries, this phenomenon can be observed in various species, from jelly fish and dog to human beings.

Another evidence of human eye evolution can be found in the fossils of trilobites, marine animals living about five hundred million years ago. One might be impressed by the fact that trilobites had light-sensitive bacteria in their eyes. Today, the scientists can perform the experiments on the remnants of these pre-historic animals with the help of X-rays.

One more stunning peculiarity is that trilobites' eyes resembled flowers by shape, and their sensors were shaped like petals. The cause is that these animals lived in the bottom of the ocean, and had to perceive the slightest changes in the light. A crab being a modern prototype of trilobites has similar eye characteristics.

To clearly understand the issue with the complexity of the human eye, one should look into the case with animals' eye systems. Let's take a turbellarian worm as a perfect illustration to the issue. Its eyes have pigment cells, and the animal is able to control and direct the photoreceptors demonstrating progressive eye system.

With the evolution, eye systems have become more advanced. For instance, some fish existing five hundred million years ago possessed a modern human's eye mechanism. Moreover, their eyes had a sort of lens typical for modern species and had the opening to protect the eye from infection.

Once the human ancestors moved from water to land, their eyes needed evolution again. The eyes of first animals' had elliptical shape and modulations in their location. For example, a deer has the eyes on two sides of his head to notice a wild animal approaching him. The predators like wolves tend to have eyes in front of their head for better perception.

In general, we still consider the evolution an imperfect process, and human eyes are imperfect either. However, even Charles Darwin thought the most beautiful thing about evolution was the variety of processes and forms coming from it. Thus, human eye can be regarded a marvelous mechanism with a certain degree of perfectness.

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