MadSci Network: Evolution

Re: Are there any advantages in being myopic?

Date: Tue Nov 30 16:55:11 1999
Posted By: Steve Mack, Post-doc/Fellow, Molecular and Cell Biology, Roche Molecular Systems
Area of science: Evolution
ID: 936330713.Ev

Thanks for the question Wilfred. As a person who wears glasses, I've wondered about this myself from time to time. Fortunately, your question includes almost everything we need to know in order to determine the answer.

Myopia is a condition which is commonly refered to as "near-sightedness" or "shortsightedness". It occurrs when your eye becomes elongated with respect to the "normal" shape it has when you have so-called 20/20 vision. Under normal circumstances, images form on the retina in the back of the eye, but when your eye is elongated, the image at forms in front of your retina, and close objects become much easier to see than distant objects. The opposite happens in the case of "far-sightedness" or hyperopia.

Your question asks about the evolutionary advantage of myopia. Evolution is a process that operates on genetic traits, so in order for there to be an evolutionary advantage to near-sightedness, there would have to be a gene that you could inherit which was responsible for that condition. However, you point out in your question that the development of myopia seems to be related to reading.

In fact, the development of myopia seems to be primarily due to environmental factors, and not to a single gene. To say this differently, you develop myopia depending on how you use your eyes. If you tend to look mostly at obects that are close up, your eye will adjust to facilitate looking at close objects by elongating. Because we have to look at so many things that are close in modern life (books, computer screens, televisions, etc.) more and more of us are becomming near-sighted. This is especially true in young children, whose eyes are still growing.

For example, a study of Alaskan Eskimos was done in the late 1960s comparing the vision of Eskimo parents and grandparents, who lived outdoors and often could not read, with that of their children and grandchildren, who had been taught to read in shcools. While none of the older generation were myopic, 60% of the children were. Similarly, many primates living in the wild have eyes which are similar to ours, but they show no signs of myopia. Yet, if you limit the vision of these animals so that they only have things to look at which are a short distance away, they develop myopia. In fact, it seems likely that until people started to read, almost no one suffered from near-sightedness.

So, I think you can see that there is not really any evolutionary benefit to being near-sighted, because myopia is not inherited. Of course, being near-sighted does make it easier to see things that are close up. However, the very fact that we are capable of developing myopia is an evolutionary advantage in and of itself. It means that we are capable of adjusting to the environment that we find ourselves in, that we aren't simply defined by our genes. If you think about the millions of years of evolution and varied environments that our ancestors survived, you will see that it is important to be able to adapt in this manner. If you are born in a place that is flat, it might be good to be somewhat far-sighted (perhaps to distingusish between predator and prey animals on the horizon). If you lived in a place where you had to examine things closely (perhaps to distinguish between good and bad foods), it might be good to be somewhat near-sighted.

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