44.2

Definition: Vestigial structures are traits that were once useful and functional but have diminished in size or function over time.
Significance: Their presence suggests a historical function for the evolution of the organism, providing insight into the organism's ancestry.

Hip Bone in Whales
- Whales evolved from four-legged land mammals.
- As they adapted to aquatic life, their hind legs were reduced in size due to lack of utility.
- The small hip bone in whales serves as evidence of their ancestors that walked on land.
Appendix in Humans
- The appendix is a short appendage in the gastrointestinal tract.
- While it has no clear function today, it may contribute mildly to the immune system.
- Historically, it likely helped digest plant materials in ancient human ancestors.
- Infection of the appendix can lead to appendicitis, which requires surgical removal to prevent severe complications.

Small Eyes in Cave-Dwelling Animals
- These structures demonstrate adaptation to an environment devoid of light.
Rudimentary Wings in Flightless Birds
- Examples include certain species of birds and insects that have lost the ability to fly.

Pseudogenes
- Definition: A pseudogene is a gene that was once functional but is no longer expressed due to mutations.
- Similar to vestigial anatomical structures, pseudogenes represent genetic remnants of evolutionary history.
- Mutations in pseudogenes occur at a faster rate because they are not subject to selection pressure; mutations can neither harm nor benefit since the gene has lost its function.
- In contrast, histone genes are protected against mutations, leading to a slower evolutionary rate.

Describe what a vestigial structure is.
- A vestigial structure is a reduced or nonfunctional trait that was once useful in the ancestor of the organism.
Identify two examples of vestigial structures.
- Hip bone in whales and appendix in humans.