Further evidence for the idea of evolution is the existence of vestigial structures. These vestiges are structures that are genetically determined but have lost some or all of their original function from the ancestral species. Oftentimes, vestigial structures are homologous to structures in related species. The way a vestige is formed is during typical evolutionary process when a structure loses its function and no longer provides a positive pressure. The loss of function can come from a change in the environment that the ancestral species originally adapted to. So long as the structure does not now present a negative pressure due to some hinderance on the species, it is considered neutral and not necessarily selected for or against. As a result, instead of losing the feature it may persist though it has no inherent value anymore. Common examples of vestigial structures are the hip bones that remain in snakes and whales. At a time, these species had ancestors that had limbs that required hips for mobility. Now that they no longer have the same limbs and are under different selective pressure, the genetics still encode for a hip bone, but it is not used. The bone is not a detractor and is not selected against but is slowly withering away over evolutionary time.
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