At a time, these species had ancestors that had limbs that required hips for mobility. Common examples of vestigial structures are the hip bones that remain in snakes and whales. As a result, instead of losing the feature it may persist though it has no inherent value anymore.

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. The loss of function can come from a change in the environment that the ancestral species originally adapted to.

The way a vestige is formed is during typical evolutionary process when a structure loses its function and no longer provides a positive pressure. Oftentimes, vestigial structures are homologous to structures in related species. These vestiges are structures that are genetically determined but have lost some or all of their original function from the ancestral species. Further evidence for the idea of evolution is the existence of vestigial structures.

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