The Selfish Gene by Richard Dawkins explains the process of why some genes are chosen on top of others. The case he directly uses is that of the eyes, explaining how it is that the "architect" that we have in our self's decides which eye color to choose for us. If we were to have a gene for blue colored eyes and a gene for brown colored eyes, only one of them would be chosen. Since brown is dominant over blue because blue can only become dominant if it has 2 alleles, then it is certain that a person with a brown and a blue allele will have brown eyes. The other gene is not lost though, it is kept inside the body, and could be passed on to future generations making it possible at some point for the 2 alleles to meet each other and therefore create blue eyes.
It is very similar to how we always choose what we believe is better. When we have the choice to get something we believe has a greater value, we take it, and we also keep that of less value for if in the future it becomes necessary. Once we don't have something valuable, we stick to the next most valuable thing we can find, or in this case, the blue eyes. The blue eyes become a matter of keeping them for later on in the trip, and using them in case we need them, since we know they may come in handy when the other choice we have is also blue eyes. Many times we have the choice of getting something we want, and usually will get the best we can, but in those cases in which we don't, we stick with what we have, and are proud to pass them on around.
Great diagram!
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