The presence of an organ in one organism that resembles one found in another has led biologists to conclude that these two might have shared a common ancestor. Vestigial organs have demonstrated remarkably how species are related to one another, and has given solid ground for the idea of common descent to stand on. From common descent, it is predicted that organisms should retain these vestigial organs as structural remnants of lost functions. It is only because of macro-evolutionary theory, or evolution that takes place over very long periods of time, that these vestiges appear.
The term ?vestigial organ? is often poorly defined, most commonly because someone has chosen a poor source to define the term. The Oxford English Dictionary (OED) defines vestigial organs as organs or structures remaining or surviving in a degenerate, atrophied, or imperfect condition or form. This is the accepted biological definition used in the theory of evolution.
In the never-ending search for scientific truth, hypotheses are proposed, evidence is found, and theories are formulated to describe and explain what is being observed in the world around us. The following are ten observations of vestigial organs whose presence have helped to flesh out the structure of the family tree that includes every living creature on our planet.