Which term describes a structure that has little or no use in modern organisms but persists from an ancestor?

Which term describes a structure that has little or no use in modern organisms but persists from an ancestor?

• A. Vestigial Structures
• B. Analogous Traits
• C. Homologous Structures
• D. Atavisms

Answer: (A)

Structures that once served a purpose in our ancestors but are now largely nonfunctional in the present organism illustrate evolution by descent with modification. These remnants persist because they don’t hinder survival and their presence reveals evolutionary relationships, even when the current life history doesn’t require their original use. A classic example is the human coccyx, a tailbone that comes from a tail our distant ancestors had. Whale pelvic bones are another example: they no longer help with locomotion on land, yet they point to a terrestrial past. This is exactly what vestigial structures describe—the persistence of a structure with little or no current use, reflecting ancestry. For comparison, analogous traits arise in separate lineages because of similar environmental pressures, not shared ancestry, so they look alike but aren’t inherited from a common ancestor. Homologous structures come from a common ancestor and may be repurposed for different functions. Atavisms are the reappearance of ancestral traits in an individual due to genetic changes. But vestigial structures specifically capture that legacy of an ancestor with reduced current function.

Structures that once served a purpose in our ancestors but are now largely nonfunctional in the present organism illustrate evolution by descent with modification. These remnants persist because they don’t hinder survival and their presence reveals evolutionary relationships, even when the current life history doesn’t require their original use. A classic example is the human coccyx, a tailbone that comes from a tail our distant ancestors had. Whale pelvic bones are another example: they no longer help with locomotion on land, yet they point to a terrestrial past. This is exactly what vestigial structures describe—the persistence of a structure with little or no current use, reflecting ancestry.

For comparison, analogous traits arise in separate lineages because of similar environmental pressures, not shared ancestry, so they look alike but aren’t inherited from a common ancestor. Homologous structures come from a common ancestor and may be repurposed for different functions. Atavisms are the reappearance of ancestral traits in an individual due to genetic changes. But vestigial structures specifically capture that legacy of an ancestor with reduced current function.