Eyes first appeared approximately 543 million years ago during the Cambrian period—the geological period that marks the rapid increase in biodiversity. According to Andrew Parker’s Light Switch Theory, vision is key for the understanding of the Cambrian.
The reason for the so-called “Cambrian explosion”—because life suddenly “exploded”—has been studied extensively, including by Charles Darwin who saw it as an argument against his theory of natural selection. Because natural selection emphasized small gradual changes over a long period of time, Darwin had a hard time understanding how can life diversity so suddenly burst into existence. The Light Switch Theory tries to bridge this gap.
According to Andrew Parker in his book “In the Blink of an Eye: How Vision Sparked the Big Bang of Evolution,” the Cambrian period is not properly described simply by its great life diversity.
This flippant approach to the most dramatic event in the history of life is misleading in the extreme, and has led to a number of false explanations for the cause of the event.[…]The Cambrian explosion is the evolutionary episode in which all animal phyla attained complex external forms. In other words, it is the event during which animal phyla changed from all looking the same to looking different.[…] By external parts of animals I refer to the materials, colours and shapes of the outer layers. These have a closer association with the environment than do with internal organizations.[…] Think of the protective spines, swimming paddles, burrowing shapes, grasping arms, eyes and colours.
Discussing Darwin’s concerns about the implausible speed of life emergence during the Cambrian, Parker’s Light Switch Theory notes:
Revolutions in evolutionary theory have occurred since Darwin’s time. Now we know that the history of life on Earth has been dominated by long periods of gradual evolution—‘micro-evolution’—or even a complete standstill. But these periods ended abruptly as the were replaced by ‘macro-evolution’—short but prolific bursts in evolutionary activity, hence a so-called ‘punctuated equilibrium’ model for evolutionary history. Darwin and others of his time cannot be blamed for overlooking macro-evolution because its discovery was a consequence of twentieth-century fossil finds and the development of modern biochemical techniques.
Andrew Parker’s Light Switch Theory postulates that once atmospheric changes during the Cambrian increased the amount of light reaching the Earth, the evolutionary benefits of seeing were great and therefore eyes rapidly emerged. Vision sparked predation because predators were able to see, pursue, and kill the prey. Hard parts assisting predation such as teeth and jaws quickly emerged. In response, protective hard parts such as shells evolved to protect smaller animals from the predators.
All animals have to be adapted to the existence of eyes not only in terms of their [the animals’] colour, but also in their shape and behaviour —all factors affecting an animal’s appearance on a retina. When this retina belongs to a predator, the image formed on it becomes a matter of life and death for the potential prey.
Andrew Parker’s Light Switch Theory not only possibly explains the reason for the Cambrian explosion, but also sets apart the eyes and vision as one of the driving forces of natural selection and evolution. His theory suggests an evolutionary reason for the overwhelming supremacy of the human vision over the other senses, and in general of the gradual natural predominance of vision over olfaction in primates. Lynne Isabelle discusses the evolution of vision in great detail in her book “The Fruit, The Tree, and The Serpent: Why We See So Well,” where she also mentions Parker’s Light Switch Theory.