Life of ‘Eye’

Humans are one of the most highly evolved creatures on Earth; a fact that we all know. I am also sure that most of us would have come across the word ‘Species’. ‘Species’ is just a criterion in the classification of organisms. There are billions of organisms out there. How did they evolve? From the cell to the bone to the skin to the eye? Did all of them emerge from a Noah’s Ark as we believe?

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Charles Darwin

No. According to scientists like Charles Darwin, all organisms weren’t just put there – they evolved. They adapted themselves to their surroundings. What’s most interesting is that most of these adaptations were accidental.

Here’s the science behind it: When a single cell undergoes division; along with the others, the DNA of a cell also divides. DNA or Deoxyribonucleic acid is found in the Nucleus of a cell. It is responsible for hereditary genes (the reason you look like your parents). For the DNA to copy properly, there is a strict process that enables certain genes to check for mistakes and repair the DNA. However, like the man, these genes are not perfect and sometimes fail to find faults.

dna eyeFor an example, let us suppose that the Reproductive cell of a female Brown Bear in the North Pole has met with a similar situation as above. So, out of the two cubs she gives birth to, one is brown, and the other is white. Now who would have an advantage? The white one, as it will camouflage better in the snow. So slowly, the white bear evolved as the Arctic Bear we know today.There are no Grizzly Bears in the North Pole.Same way, all these accidental adaptations have led to the new species we know today.

Now let’s go smaller. The Eye is one of the most complex organs in our body. Surely, it must have had its origin, too.

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It has been commonly accepted that the first forms of the eye were proteins called opsins formed about 540 million years ago. Opsins detected photons(Light signals) and sent signals to the brain. As they moved on, opsins became ‘eyespots’ in unicellular organisms like Euglena, as a small red area near their rear end. These eyespots were only able to differentiate light from dark, but this proved useful as organisms with ‘eyespots’ were able to reproduce better by sensing night. Eyespots are said to have changed 40-65 times alone.

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Opsins are the colored strings in between

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Next, there started to be a small depression in the animal Planaria (flatworm). With a deeper depression, there were more photoreceptors (small molecules that detect light) which immediately gave a more precise picture and the organism was able to identify the direction of light.

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Planarian Eyes

Next, the depression started to fold into a pouch. As the opening of this ‘pouch’ started getting smaller, the depression deepened further, giving organisms a more accurate picture.

As thousands of years passed on, the eye’s overall structure began to differ. The growth of more transparent cells prevented infections. Improvements included protection from UV rays, vision in water and differentiation of colors.

Another remarkable improvement in eyes was the formation of Lens. Lens are a transparent covering over the eye and can alter light, so as to focus an image on the retina. Lens are made of a molecule called Crystallin, which is one of the most specialized proteins in our body. Different types of crystallin give rise to various kinds of eyes, like how our eyes are different from a cat’s or an octopus’.

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Lens of the Eye

The eye is one of the smallest parts of a body. If such a small organ itself has such a vast history, enough to cover one full Wikipedia page, then what would be the history of the heart? Or the lungs? Or the brain?

Indeed, it is rightly said that there are so many secrets to life. Will man recover them all?

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