Download Vestigial structures have no function but may still be

Vestigial structures have no function but may still be inherited to
maintain fitness.
LEARNING OBJECTIVES [ edit ]
Detail the connection between evolutionary processes and the existence of vestigial structures
Define vestigial
KEY POINTS [ edit ]
Structures that have no apparent function and appear to be residual parts from a past ancestor
are called vestigial structures.
Examples of vestigial structures include the human appendix, the pelvic bone of a snake, and the
wings of flightless birds.
Vestigial structures can become detrimental, but in most cases these structures are harmless;
however, these structures, like any other structure, require extra energy and are at risk for
disease.
Vestigial structures, especially non-harmful ones, take a long time to be phased out since
eliminating them would require major alterations that could result in negative side effects.
TERMS [ edit ]
adaptation
modification of something or its parts that makes it more fit for existence under the conditions of
its current environment
vestigial structure
genetically determined structures or attributes that have apparently lost most or all of their
ancestral function in a givenspecies
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Vestigial Structures
Some organisms possess structures with
no apparent function at all and appear to
be residual parts from a past ancestor. For
example, some snakes have pelvic bones
despite having no legs because they
descended from reptiles that did have legs.
Another example of a structure with no
function is the human vermiform
appendix . These unused structures
without function are called vestigial
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structures. Other examples of vestigial structures are wings on flightless birds such as the
ostrich (which may have other functions), leaves on some cacti, traces of pelvic bones in
whales, and the sightless eyes of cave animals.
Vestigial appendix
In humans the vermiform appendix is a vestigial structure; it has lost much of its ancestral function.
Vestigial Structures in Evolution
Vestigial structures are often homologous to structures that are functioning normally in
other species. Therefore, vestigial structures can be considered evidence for evolution, the
process by which beneficial heritable traits arise in populations over an extended period of
time. The existence of vestigial traits can be attributed to changes in the environment and
behavior patterns of the organism in question. As the function of the trait is no longer
beneficial for survival, the likelihood that future offspring will inherit the "normal" form of it
decreases. In some cases the structure becomes detrimental to the organism.
However, in many cases the structure is of no direct harm, yet 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). This provides some selective pressure for the removal of
parts that do not contribute to an organism'sfitness. A structure that is not harmful will take
longer to be 'phased out' than one that is. However, some vestigial structures may 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.
The vestigial versions of the structure can be compared to the original version of the structure
in other species in order to determine the homology of a vestigial structure. Homologous
structures indicate common ancestry with those organisms that have a functional version of
the structure. Vestigial traits can still be considered adaptations. This is because an
adaptation is often defined as a trait that has been favored by natural selection. Adaptations,
therefore, need not be adaptive, as long as they were at some point.