Blind fish -- evidence of de-volution

Don't you find it strange that when people go blind we regard it as tragic, but when cave-dwelling fish go blind it's hailed as 'evolution in action'?

There are cave-dwelling fish with a mutational defect that causes them to have scar tissue where they would normally have eyes. Usually, this is an obvious disadvantage, but in a totally dark cave, eyes are not necessary. In fact, it is actually a benefit not to have eyes because they are delicate and easily injured by sharp rocks.

So blind cave-dwelling fish are better suited to that environment.

But is this really a legitimate example of 'evolution'? Evolution is meant to explain how new DNA information arose to turn non-sighted creatures into sighted creatures. But in the case of blind cave fish we have actually witnessed de-volution—because the information for eyes has been corrupted and lost. Once again, 'evolution' goes in the wrong direction.