Vision is a sense that a majority of animals have and seems almost essential in life. We almost take this crucial ability for granted. to How did the ability to see things arise, and what makes this possible?
Vision was first used by unicellular organisms that had eyespots that had photoreceptor proteins that detected light. This was a very primitive form of vision that allowed these organisms to sense how bright their surroundings were. This was essential since they used photosynthesis to provide energy and knowing if the sun was out gave these organisms an evolutionary advantage. This rudimentary eye evolved over time and worked like a pinhole camera by having a small hole where light entered.
Today, most animals have developed a more sophisticated way to see. They use cones and rods to process light and perceive a detailed image of our surroundings. They are made up of many molecules including one called retinal that is made up of carbon, hydrogen, and oxygen atoms. This molecule helps transmit the data from the light around us into chemical signals our brain can understand. Retinal has many equilibriums where the atoms are arranged in a stable manner. When photons enter into the eye, they can add energy to this molecule and change the way the atoms are organized in the molecule. Each molecule changes its arrangement based on the frequency of the light wave and this allows us to tell the difference between different colors of light.
In addition to the retinals, there are also opsins in the rods and cones. When a retinal is changed it pushes an opsin protein which releases a transduction molecule that cause a chain reaction, eventually sending a signal to the brain. The brain then takes these signals from the red, green, and blue cone cells and uses them to determine what color the image is since each color creates a different signal to the brain.
This process is very similar to how most animals see and indicates that vision is something that evolved in our common ancestor billions of years ago.
I think it’s very interesting how these molecules are the keys for vision all across the animal kingdom and how the process for something that is used constantly is much more complicated than you would expect it to be. Many biological processes make use of the chemical and physical properties of molecules.