The correct answer is option 1 - Tailbone. A vestigial organ is an organ that has lost its original function over the course of evolution. The tailbone, also known as the coccyx, is a small, triangular bone located at the base of the vertebral column in humans. It is a remnant of a tail that our ancestors once had, which was used for balance and mobility. Over time, as humans evolved and the need for a tail diminished, the tailbone gradually became smaller and lost its function. Although the tailbone may not serve any specific purpose in humans now, it can still be prone to injury or discomfort. Despite its vestigial nature, the tailbone serves as an attachment point for various ligaments and muscles in the pelvic region.