What explains persistence of vestigial structures?
Vestigial structures are often those that are present but have no current function. In almost all cases, related species have the structure in a functional form suggesting that the structure has been retained from an ancestor that had and used the structure. During development an organism will form the same structures regardless of whether they will be used. However, those individuals that experience mutations that reduce the size of an unused structure will suffer no detriment and may gain an advantage due to avoiding the energetic cost of making a useless structure. Thus, over time selection will favor reductions in the vestigial structure. However, this will take time because it may be rare to have a mutation that reduces the organ in question and does not have other detrimental consequences. Also, as the organ gets smaller the potential energetic benefit to a further reduction is reduced. So, it may take a very long time for a vestigial organ to be fully lost. Examples of vestigial
