What is vestigial trait?

A vestigial trait is an organ whose function was lost over time due to the evolution of the species. This can be clearly seen in many animals, for example, the whale and the dolphins have some bones that in the past formed parts of arms and legs. In humans, the appendix and coccyx are examples or vestigial trait.

Vestigial trait (or vestigiality) is biological trait of organisms to retain organs, which have seemingly lost the original function. The vestigial trait may refer to many genetically determined features that are either morphological, behavioral, or physiological. Most common example for vestigial organ is appendix which has lost significant digestive function, but it still has immunological roles and is useful in maintaining gut flora.