What is a characteristic of vestigial structures?

Vestigial structures are characterized by having no apparent function in the current context of the organism but resemble structures that were functional in their ancestors. This concept is important in evolutionary biology, as it provides evidence for the descent from common ancestors and the changes that occur over time within species. An example of a vestigial structure is the human appendix, which is much smaller and less functional than the cecum found in some herbivorous ancestors that required it for digesting cellulose.

The other options present characteristics that do not align with the definition of vestigial structures. Clear current functions would imply that the structures are no longer vestigial and serve a purpose in the organism's life. Similarly, the appearance at later stages of development or the provision of a function in modern organisms does not account for the historical context or the lack of present functionality associated with vestigial traits. Thus, the correct understanding of vestigial structures centers around their ancestral lineage and the diminished functionality seen in contemporary organisms.