How do vestigial structures relate to evolution?

Hint: Vestigial structures are the structures that remained or retained during the process of evolution but lost their primary functions and actual size.

Complete answer:
Evolution is the process by which different organisms evolve from each other over the course of time. The favorable or advantageous characters were selected over time, and the non-favorable characters were eliminated from the population. The organs or individuals that lost their functions were either modified or removed.
Vestigial structures are the structures that have lost their function over time but are still found in the organisms. They are the residual parts of the ancestors. They do not serve any current function to the organisms they are present on but served important functions in their ancestors. A few examples of vestigial structures are- human tailbone, wisdom teeth, human appendix, pelvic bone of a snake, wings of flightless birds, etc.

These structures support the theory of evolution as-

1.They explain how species have evolved and favored the production of structures that were beneficial to them while eliminating or delimiting the ones that were no longer in use.
2.It explains how individuals have evolved from their ancestors and prove ancestral origin.
Many vestigial structures are homologous to present structures. This can be considered as evidence for evolution.
3.It also supports the theory of natural selection, where the favorable characters are selected and passed on to the next generations, and the others are removed or made non-functional. Since these structures do not affect the reproductive process, they are not eliminated.
4.It explains how organisms have evolved their structures by using them accordingly with time and requirements.
5.The study of vestigial structures is done to find evidence of evolution.

Note: Vestigial structures are often confused with atavism. Atavism is the reappearance of a trait or an organ due to gene recombination. These traits went missing during some generations and appeared again in the species. The appearance of limbs in limbless organisms is one of its examples. Vestigial organs do not disappear or reappear in the population.