Eyeless fish in caves
‘We read about fish that live in caves. They can’t see, and they have scars where most fish have eyes. Were they created like this?’
No. Mutation and selection have changed them from a state in which they had eyes to one in which they don’t. The following is almost certainly what happens in such situations.
A population of fish that have eyes begins to live in underground environments that have no light. Their eyes are then useless to them. However, organs do not ‘degenerate’ just because they are useless. The information to produce eyes is copied and passed on, generation after generation.
Even fish that live in light occasionally have copying ‘mistakes’ as this information is transmitted. These ‘mistakes’ are called mutations. They corrupt and damage the information. When a fish living in a light environment has such a mutational defect which causes its offspring to have no eyes, this defect does not have very much chance of being passed on generation after generation.
The reason is simple—a fish without eyes is normally at a tremendous disadvantage. Sight helps fish catch their food and avoid being caught for food themselves. Natural selection will thus tend to eliminate this defect.
But what about those fish that have come to live in caves? Sooner or later, the same eyeless defect will occur here as well. Only this time, it does not give any disadvantage, so it is not eliminated. In fact, it gives advantage. The fish that have eyes can bump into things and injure their eyes, also they can get diseases of the eyes, both possibly leading to death. The fish that carry the eyeless (defective) information can’t get any of these problems. These eyeless fish thus have a greater chance of passing on their genetic information (carrying this defect) and so in time, natural selection will ensure that all the fish are eyeless.
Note that this is a ‘downhill’ change. Complex, functional information coding for eye manufacture has been corrupted or lost. Such a decay process gives no evidence at all for the belief that complex organs have arisen by such processes—it only shows how this information can be lost in a fallen world.