What are vestigial structures indicative of in evolutionary biology?

Vestigial structures provide evidence of evolutionary history by indicating remnants of organs or features that were functional in ancestors of a species but have lost their original function over time. These structures persist in modern organisms, often reduced in size or altered in use, reflecting a lineage’s adaptation, changes in environment, or different modes of life.

For example, the human appendix is considered a vestigial structure; it is thought to have been part of a digestive system that was more complex in herbivorous ancestors. In modern humans, the appendix has largely lost its original digestive function but remains as a small pouch in the digestive system. The presence of such structures supports the concept of descent with modification, where species undergo changes based on their evolutionary past while adapting to new environments or lifestyles. Thus, the identification of vestigial structures strengthens the argument for the evolutionary connections between species, showcasing their shared ancestry and the adaptations they have undergone over time.