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Bacteria, being the smallest organisms on the planet, also possess the smallest eyes on the planet. Many species of bacteria have at least one pigmented spot on them known as an eyespot, which has been shown to be an evolutionary advantage (compared to bacteria without eyespots) in a lit environment. But how has this eyespot come into existence? What makes it an evolutionary advantage? And what would it look like to look through the eyespot of a bacteria. Through current theory on the evolution of the eye, logic, and some graphic manipulation, these questions shall be answered.



The Theoretical Development of the Bacterial Eyespot

Many bacteria are affected by mutation due to some random genetic change. Many bacteria do not immediately show change, where as others may show change immediately in the form of a physiological change. Some of these random and non-observable changes are the ones immunobiologists are concerned with today. Certain species of E.coli, for instance, are resistant to certain streptomyocin (Snustad, 361). This is not because the bacteria adapt by building a resistance. Rather it is because of a random mutation which made one or a few bacteria able to live in an environment with the antibiotic. The bacteria then reproduce to make more copies of themselves, and have therefore evolved from the original population.

Now that random mutation is understandable, imagine a population of plain, primitive bacteria (no specific size, shape, etc.). There are trillions of them scattered throughout the world. Imagine that one out of every million of these trillion bacteria experience a mutation which allows it to have a pigmented surface. That means we have one million bacteria with some kind of a light-capturing surface on them. A few out of these million bacteria develop the pigmented spot over an opaque surface connected somehow with the rest of the internal network of the cell (Patton). These few cells, have just developed a primitive type of vision.


Advantages of the Bacterial Eyespot

Comparing the advantages of a bacterial eyespot to one without, are much like comparing the advantages of a person with eyes to a person without eyes. A bacteria with an eyespot, will most likely have a higher amount of awareness of their environment. The bacteria's eyespot could help them distinguish between different types of food, much as the human eye helps to distinguish between poisonous and non-poisonous foods. The eyespot could also help them to distinguish between members of its own species and members of different species, which would cause a higher probability of mating in a sexually reproducing species. This can also be seen in humans, since many people judge a human by site, although sometimes deceiving. Possessing the eyespot could also help a bacteria to find more intense light sources which can help the bacteria drive the processess needed for its survival (such as photosynthesis in E.acus at right). This, however, can not be seen so much in humans as in plants, because humans supposedly have no necessary light-driven processes.

Now go back to your imaginary population of bacteria with the few bacteria with the eyespots are now present. These new bacteria have a higher fitness due to their evolutionary advantages over those without eye spots. It seems logical that these bacteria would have a higher survival rate than those without eyespots, because they can find food, mates, and can also avoid predators much more efficiently. Over many generations, it would be expected that the new bacteria would increase exponentially in numbers, forming their own populations which would eventually diversify and develop many other sub-populations of bacteria. Some will be photosynthetic, while other bacteria will consume their energy from chemical sources. Some will develop into predators, while others become prey. Some remain single-celled, while others experience a random mutation which causes them to become multi-cellular. Yet all species will have one thing in common, a common ancestor from which they received their genetic information.










Looking Through the "Eye" of Bacteria

Since the bacterial eyespot is a small and nearly flat surface, little can be told as far as pictorial information is concerned. Color is not sensed due to a lack of different types of receptors. Movement can also be difficult to detect if an environment is not well-lit, or has too high an intensity of light. To better visualize the possible resolution of bacteria, Placopecten, a species of mollusk, is shown (at right) in a comparison between human color vision and hypothetical bacterial vision.