What is a vestigial organ?

Answer 1

a Vestigial organ is an organ of the body that doesn't seem to serve any useful purpose, but similar organs in other animals do. It is supposed that our early ancestors had use for the organ but now, as we have evolved, the organ has become redundant. As we continue to evolve, we may lose it altogether.

If the theory of evolution is correct, then many animals could be found with vestigial organs. For many years, it was thought that the appendix was vestigial and served no purpose. It was believed to be a vestigial form of the caecum found in many herbivores. Indeed, it probably is. However, we now know that it is wrong to believe the human appendix has no function. It is very important in developing the immune system in foetus and young child and may have a role in recycling haemoglobin from dead red blood cells. But it certainly has lost its role in digestion.

It is interesting that organs are sometimes described as vestigial, simply because the scientists haven't yet worked out their real use.