Final answer:
Vestigial structures, such as the nonfunctional wings of an ostrich, are evidence for the theory of common descent.
Step-by-step explanation:
Vestigial structures are a type of evidence for the theory of common descent. These structures are body parts that have lost their original use through evolution. The nonfunctional wings of an ostrich are an example of vestigial structures.
They suggest that the ostrich evolved from ancestors that used their wings for flight, but over time, the wings became reduced and lost their flying function. Vestigial structures provide evidence for common ancestry because they show that different populations of organisms evolved from a common point.