The evolution of the human eye is an amazing feat that didn’t happen overnight with the first photo receptors dating back to 540 million years ago! Of course there where a lot of changes that took places to get from a simple photo receptor to a true viable eye. With the help of UnbelievableFacts.com and Wikipedia here’s a quick explanation of how it happened.
The earliest predecessors of the eye were photoreceptor proteins, found in unicellular organisms, called ‘eyespots’. Eyespots can only sense brightness. Then, it became important for organisms to be able to discriminate the direction that light was coming from. This was made possible by the multicellular eyepatch, gradually depressed into a cup, which first granted the ability to discriminate brightness in directions, then in finer and finer directions as the pit deepened.
The development of the retina came next. When a photon is absorbed by the chromophore(part of a molecule responsible for its colour), a chemical reaction causes the photon’s energy to be transduced into electrical energy and relayed, in higher animals, to the nervous system. These photoreceptor cells form part of the retina, a thin layer of cells that relays visual information to the brain.
Then, things happened very quickly. The next stage was the discovery that reducing the width of the light opening became more efficient at increased visual resolution, than simply deepening the cup. These kind of eyes still lacked a cornea or lens which, sure enough, came to be in the next stage of eye evolution.
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