Vestigial structures are anatomical features or traits in an organism that were inherited from ancestors but have lost most or all of their original function through evolution. These structures are typically reduced in size or complexity compared to their fully functional counterparts in ancestral species
. They arise when a lineage experiences changes in selective pressures, making the original function of the structure less necessary or obsolete. As a result, natural selection no longer maintains the structure's elaboration or function, leading to its reduction or loss over time. Despite their reduced function, vestigial structures are homologous to fully functional structures in related species, providing strong evidence of common ancestry and evolutionary history
. Examples include:
- Dewclaws in animals like pigs and dogs, which are reduced digits that no longer support weight
- Claws on the wings of some birds such as hoatzin chicks and ostriches, reflecting clawed ancestors
- The human appendix, which is a remnant of a larger digestive structure in herbivorous ancestors
- Pelvic bones in snakes, which indicate descent from legged reptiles
- Goosebumps in humans, a vestigial reflex from when body hair could be raised to appear larger to predators
Vestigial structures can sometimes still serve minor or secondary functions, but their original primary function is lost or greatly diminished
. They are considered important evidence for evolution, showing how species have changed over time in response to their environments
. In summary, vestigial structures are evolutionary remnants-features inherited from ancestors that are now reduced, nonfunctional, or repurposed, reflecting the organism's evolutionary past.
