vestiges

A vestige is a trace or remnant of something that once existed but no longer exists in its original form. In biology, the term refers to a structure, behavior, or gene that has lost most or all of its ancestral function, yet remains within a living organism. The word comes from Latin vestigium, meaning a trace or footprint.

Vestigial structures are anatomical features that were functional in ancestors but are reduced or obsolete in modern organisms. They provide evidence for evolution by showing how traits can persist while their original use declines. Some vestigial traits still have minor or different functions; others are largely inert. In humans, notable examples include the coccyx, a remnant of a tail; the appendix, whose role is debated but is not essential for digestion; and the muscles that can cause goosebumps, vestiges of body hair control in our mammalian ancestors.

Other clear examples occur in other species. Many flightless birds retain wings that are no longer used for flight, while snakes and whales bear bones that resemble hind limbs but no longer serve locomotion. The plica semilunaris in the human eye is a small remnant of a third eyelid, and certain genes have become vestigial as they accumulate disabling mutations, such as pseudogenes that once produced functional proteins.

Vestigiality also appears in development; embryos may briefly display ancestral features, such as tails or gill slits, before maturation. Studying vestiges helps scientists infer evolutionary relationships and the history of life on Earth, illustrating how current biology bears the marks of past forms and functions.