What is an example of a vestigial structure in humans?

The appendix is considered a vestigial structure in humans because it is a remnant of a larger cecum that was more functional in the diets of our herbivorous ancestors. In those ancestors, the cecum helped in the digestion of cellulose from plant material. As human diets evolved and became less reliant on raw plant matter, the appendix became less essential for digestion. While it still plays a minor role in the immune system and gut flora management, it is not critical for survival and is viewed as a structure that has lost much of its original function over the course of evolution.

In contrast, the heart is a vital organ necessary for pumping blood and maintaining circulation, and eyes are crucial for vision. Bones also serve essential structural and protective functions within the body. These structures are not vestigial, as they are actively involved in important physiological processes, whereas the appendix has an evolutionary background that signals a reduction in its original importance.