What are vestigial organs?
Q: What are vestigial organs?
A: Vestigial organs are organs of the body which are smaller and simpler than those in related species. They have lost, or almost lost, their original feature and provide evidence for evolution.
Q: How do vestigial organs occur?
A: Vestigial organs occur in animals (and plants) which have changed their style of life from their ancestors. For example, snakes lost their legs as their system of movement changed.
Q: What is an example of a vestigial organ in humans?
A: The human vermiform appendix is an example of a vestigial organ in humans. It was much larger and stored microbes which produced cellulase to break down plant cell walls but is no longer used since leaves are not part of the main diet for humans.
Q: Why do unused organs usually degenerate?
A: Unused organs usually degenerate because they require energy for development, maintenance, and weight but don't provide any benefit to the organism's fitness so there is selection pressure against them. In addition, they can be more prone to diseases such as infection or cancer if left unused.
Q: Can selection turn a vestigial organ into something useful?
A: Yes, occasionally selection can turn a vestigial organ into something useful - this phenomenon is known as exaptation. An example would be mammalian ear ossicles which were once bones in the jaw of early proto-mammals called Therapsida.
Q: What did researchers observe about cave-dwelling amphipod Gammarus minus?
A: Researchers observed active selection against the cave-dwelling amphipod Gammarus minus' vestigial eyes when mating - paired males had smaller eye sizes than unpaired males on average due to higher fertility rates associated with small eyes freeing up more nervous system resources to process other sensory inputs instead.
