Some vestigial structures persist due to limitations in development, such that complete loss of the structure could not occur without major alterations of the organism’s developmental pattern, and such alterations would likely produce numerous negative side-effects. This provides some selective pressure for the removal of parts that do not contribute to an organism’s fitness, but a structure that is not directly harmful will take longer to be ‘phased out’ than one that is.
If there are no selection pressures actively lowering the fitness of the individual, the trait will persist in future generations unless the trait is eliminated through genetic drift or other random events.Īlthough in many cases the vestigial structure is of no direct harm, all structures require extra energy in terms of development, maintenance, and weight and are also a risk in terms of disease (e.g., infection, cancer). Letter c in the picture indicates the undeveloped hind legs of a baleen whale.
\): Whale Skeleton: The pelvic bones in whales are also a good example of vestigial evolution (whales evolved from four-legged land mammals and secondarily lost their hind legs).
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