500 million the number of years the human eye has been in existence. The origins of ‘sight’ go back 700 million years when earth was inhabited only by single-celled amoeba-like animals, algae, corals and bacteria. At this time the first light sensitive chemicals, known as opsins, made their appearance and were used in rudimentary ways to sense day from night.
Over the next 200 million years these simple light-sensitive cells slowly and progressively became better at detecting light until around 500 million years ago when they closely resembled the cone cells of our present day eyes.
As eyes were evolving from crude, light-sensitive cups to more complex systems, the Earth was also undergoing a dramatic shift. A complex interplay of environmental changes were setting the stage for large, active creatures to evolve. And they did just that, with an outburst of speciation that is now known as the Cambrian explosion. It was during this time that some eyes became more complex and specialized, and began to take on different shapes and colours.
Due to the diversity of eye types around the world, scientists used to believe that eyes had many independent origins. Advances in technology helped us learn more about the molecular structure of eye, and showed that proteins known as opsins are the foundation of all eyes in all creatures. This commonality confirms that all organisms with eyes, at one point, shared a common ancestor.
Credit : Science World
Picture Credit : Google
