Sight: Envision Life Without It

In the battle to survive, wouldn’t vision be important? Being aware of your surroundings creates formidable predators and elusive prey. Our ancestors lucked out on the ability to see, and for that, we thank them. 500 million years ago, multicellular animals began appearing, evolving new ways to fill ecological niches. The Cambrian Explosion, a significant event in evolutionary history, was predominantly caused by the evolution of eyes.

The Cambrian was a bizarre time in evolutionary history. From simple unicellular organisms sprung the first-ever animals. These animals were just beginning to form, mostly as shelled arthropods: the ancestors of today's crustaceans, insects, and spiders. All of this occurred underwater, as nothing could survive on land yet, and it happened relatively spontaneously. The reason for this sudden explosion of life is heavily debated. Some researchers say it was due to an increase in oxygen levels in the atmosphere, a snowball earth, or an increase in carbon or methane. Environmental impacts will inevitably have some effect on life, but it is not the main reason for this sudden diversification of life. Where would we be today if not for the eruption of life over 500 million years ago giving us the ability to see the world around us? Just having a ripe environment for animals does not elicit such a drastic explosion of life. 

The first known evolution of a complex eye was in a hard-shelled marine arthropod called a trilobite, one of the most well-known animals of the Cambrian. Nautiluses are another animal from the Cambrian period which still exists today and possesses a completely different eye structure. Their eyes are like pinhole cameras and lack lenses or cornea. Yet another animal is Anomalocaris which had sharp vision and stalked, compound eyes (similar to that of a house fly); sometimes reaching up to two inches in diameter. With such a wide diversity of evolving eyes, these creatures quickly filled completely new niches. Anomalocaris used its good vision to hunt trilobites while the trilobites used its vision to escape and burrow in previously untouched sediment. The evolution of eyes created a need and ability to be on the move, hunt, and scavenge for food. Where once all life was quiet and still, this explosion of life emerged with battles between predator and prey. 

With a new surge of animals investigating the ocean world with their brand-new vision, populations grew larger as species spread out in search of better territory. Mating was significantly easier now that animals could move around and actually see their mate. Although the environment needed to have been at the correct levels in order for animals to thrive, I still insist that life would not have gotten nearly as far as it has without the evolution of vision. Some researchers claim that a rise in oxygenation up to today’s levels caused the Cambrian explosion, but that claim rests upon outdated data. Research from 2015 did not find a “statistically significant increase in the proportion of oxic to anoxic water at the boundary between the Ediacaran and the Cambrian,” (Fox). So although oxygen is vitally important to animals in order to perform aerobic respiration, it was not the main cause of the sudden appearance of diverse life. 

Another theory put forward is that the Cambrian Explosion was caused by a Snowball Earth event, which itself is a hypothesis. Global coverage of ice on the planet would surely have an effect on life, however, the issue with this theory is its timing. The two theorized Snowball Earths near this period occurred around 635 million years ago and 580 million years ago. According to paleontologist and evolutionary biologist Charles Marshall, not only were the Snowball Earths too early to have caused so much diversity, but it is “hard to see how a major environmental catastrophe could have led to fundamentally new levels of developmental and morphological organization.” Many factors played into the reasoning behind the sudden appearance of major life forms during the Cambrian Explosion, but the main factor that helped push life forwards was the evolution of sight. 

The Cambrian Explosion saw the development of the first ancestors for many of the major animal groups we see today. The incredible diversity of life during this period over 500 million years ago is still not fully understood. We may never have a conclusive answer for what caused this era, but it is clear that vision was an incredibly important main factor. Sight is one of the most important senses we possess; most people couldn’t imagine a world where it didn’t exist. We create visual media every day, whether it be movies, TV, plays, photos, or videos. The development of sight would surely lead to an explosion of life.