Visualizing the Evolution of Vision and the Eye
View the high-resolution version of this graphic.
Roadmapping the Evolution of the Eye
Throughout history, numerous creatures have evolved increasingly complex eyes in response to different selective pressures.
Not all organisms, however, experience the same pressures. It’s why some creatures today still have eyes that are quite simple, or why some have no eyes at all. These organisms exemplify eyes that are “frozen” in time. They provide snapshots of the past, or “checkpoints” of how the eye has transformed throughout its evolutionary journey.
Scientists study the genes, anatomy, and vision of these creatures to figure out a roadmap of how the eye came to be. And so, we put together an evolutionary graphic timeline of the eye’s different stages using several candidate species.
Let’s take a look at how the eye has formed throughout time.
Where Vision Comes From
The retina is a layer of nerve tissue, often at the back of the eye, that is sensitive to light.
When light hits it, specialized cells called photoreceptors transform light energy into electrical signals and send them to the brain. Then the brain processes these electrical signals into images, creating vision.
The earliest form of vision arose in unicellular organisms. Containing simple nerve cells that can only distinguish light from dark, they are the most common eye in existence today.
The ability to detect shapes, direction, and color comes from all of the add-ons evolution introduces to these cells.
Two Major Types of Eyes
Two major eye types (Read more...)