Life first emerged approximately 3.75 billion years ago from the swirling broth of the prebiotic soup. The process leading to its appearance is only partially understood, but has several possibilities. The harsh conditions on earth at the time would have permitted only an organism capable of withstanding such bleak surroundings. It would have been very different from any alive today. Survival of any life form in that environment would have required analysis and interaction with its birthplace habitat, skills that would require sensory abilities. Such sensory understanding would have been essential for, and crucial to, life’s evolution.
Sight is but one member of a family of sensory abilities, yet for most creatures it is a dominant and pivotal one. But sight is probably not the first sense acquired by those early cells, nor were the necessary components of vision secured for the purpose of sight. As often occurs, evolution co-opted various molecules that were assembled for other purposes. These changes and biochemical redirection leave traces suggesting the path of early photoreception.
The witness and progress of photoreception is a fascinating window on evolution with a perspective unlike any other because it includes eyes. We will review what is known about the evolution of photoreception and the development of vision, not necessarily in chronological order, but rather in an order that illustrates the goal in conjunction with the progress. Along the way, we will comment on and discuss cutting edge research currently ongoing across the world.
This is the story of how eyes evolved.