You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an alternative browser.
You should upgrade or use an alternative browser.
someone biology help please!!!?!?!?
- Thread starter Galaxy
- Start date
Vestigiality describes homologous characters of organisms which have seemingly lost all or most of their original function in a species through evolution. These may take various forms such as anatomical structures, behaviors and biochemical pathways. Some of these disappear early in embryonic development, but others are retained in adulthood. Although the term serves a purpose in many gross phenotypic characteristics, vestigial has probably little applicability to DNA sequences, be they genes or non-coding sequences. The term junk DNA is a revealing example. It is a value or judgmental term which has become less utilized in genetics as many of the sequences once believed to be “junk” have been discovered to have a function.
Vestigial structures are often called vestigial organs, although many of them are not actually organs. These are typically in a degenerate, atrophied, or rudimentary condition,[1] and tend to be much more variable than similar parts. Although structures usually called "vestigial" are largely or entirely functionless, a vestigial structure may retain lesser functions or develop minor new ones.[2] However, care must be taken not to apply the label of vestigiality to exaptation, in which a structure originally used for one purpose is modified for a new one. For example, the wings of penguin or ostrich would not be vestigial, as they have been modified for a substantial new purpose (underwater locomotion or display respectively), while Darwin pointed out that those of an emu would be, as they have no major function now.
Vestigial characters range on a continuum from detrimental through neutral to marginally useful. Some may be of some limited utility to an organism but still degenerate over time; the important point is not that they are without utility, but that they do not confer a significant enough advantage in terms of fitness to avoid the random force of disorder that is mutation. It is difficult however to say that a vestigial character is detrimental to the organism in the long term - the future is unpredictable, and that which is of no use in the present may develop into something useful in the future. Vestigiality is one of several lines of evidence for biological evolution.
Contents
[hide]
* 1 History
* 2 Common descent and evolutionary history
* 3 Examples
o 3.1 Animals
+ 3.1.1 Humans
o 3.2 Plants and other organisms
* 4 See also
* 5 References
* 6 External links
[edit] History
The blind mole rat (Spalax typhlus) has tiny eyes completely covered by a layer of skin.
Vestigial structures have been noticed since ancient times, and the reason for their existence was long speculated upon before Darwinian evolution provided a widely-accepted explanation. In the 4th century BC, Aristotle was one of the earliest writers to comment, in his History of Animals, on the vestigial eyes of moles, calling them "stunted in development".[3] However, only in recent centuries have anatomical vestiges become a subject of serious study. In 1798, Étienne Geoffroy Saint-Hilaire noted on vestigial structures:
“ Whereas useless in this circumstance, these rudiments... have not been eliminated, because Nature never works by rapid jumps, and She always leaves vestiges of an organ, even though it is completely superfluous, if that organ plays an important role in the other species of the same family.[4] „
His colleague, Jean-Baptiste Lamarck, named a number of vestigial structures in his 1809 book Philosophie Zoologique. Lamarck noted "Olivier's Spalax, which lives underground like the mole, and is apparently exposed to daylight even less than the mole, has altogether lost the use of sight: so that it shows nothing more than vestiges of this organ."[5]
Charles Darwin was very familiar with the concept of vestigial structures, though the term for them did not yet exist. He listed a number of them in The Descent of Man, including the muscles of the ear, wisdom teeth, the appendix, the tail bone, body hair, and the semilunar fold in the corner of the eye. Darwin also noted, in On the Origin of Species, that a vestigial structure could be useless for its primary function, but still retain secondary anatomical roles: "An organ serving for two purposes, may become rudimentary or utterly aborted for one, even the more important purpose, and remain perfectly efficient for the other.... [A]n organ may become rudimentary for its proper purpose, and be used for a distinct object."[6]
In the first edition of On the Origin of Species, Darwin briefly mentioned inheritance of acquired characters under the heading "Effects of Use and Disuse", expressing little doubt that use "strengthens and enlarges certain parts, and disuse diminishes them; and that such modifications are inherited".[7] In later editions he expanded his thoughts on this,[8] and in the final chapter of the 6th edition concluded that species have been modified "
Vestigial structures are often called vestigial organs, although many of them are not actually organs. These are typically in a degenerate, atrophied, or rudimentary condition,[1] and tend to be much more variable than similar parts. Although structures usually called "vestigial" are largely or entirely functionless, a vestigial structure may retain lesser functions or develop minor new ones.[2] However, care must be taken not to apply the label of vestigiality to exaptation, in which a structure originally used for one purpose is modified for a new one. For example, the wings of penguin or ostrich would not be vestigial, as they have been modified for a substantial new purpose (underwater locomotion or display respectively), while Darwin pointed out that those of an emu would be, as they have no major function now.
Vestigial characters range on a continuum from detrimental through neutral to marginally useful. Some may be of some limited utility to an organism but still degenerate over time; the important point is not that they are without utility, but that they do not confer a significant enough advantage in terms of fitness to avoid the random force of disorder that is mutation. It is difficult however to say that a vestigial character is detrimental to the organism in the long term - the future is unpredictable, and that which is of no use in the present may develop into something useful in the future. Vestigiality is one of several lines of evidence for biological evolution.
Contents
[hide]
* 1 History
* 2 Common descent and evolutionary history
* 3 Examples
o 3.1 Animals
+ 3.1.1 Humans
o 3.2 Plants and other organisms
* 4 See also
* 5 References
* 6 External links
[edit] History
The blind mole rat (Spalax typhlus) has tiny eyes completely covered by a layer of skin.
Vestigial structures have been noticed since ancient times, and the reason for their existence was long speculated upon before Darwinian evolution provided a widely-accepted explanation. In the 4th century BC, Aristotle was one of the earliest writers to comment, in his History of Animals, on the vestigial eyes of moles, calling them "stunted in development".[3] However, only in recent centuries have anatomical vestiges become a subject of serious study. In 1798, Étienne Geoffroy Saint-Hilaire noted on vestigial structures:
“ Whereas useless in this circumstance, these rudiments... have not been eliminated, because Nature never works by rapid jumps, and She always leaves vestiges of an organ, even though it is completely superfluous, if that organ plays an important role in the other species of the same family.[4] „
His colleague, Jean-Baptiste Lamarck, named a number of vestigial structures in his 1809 book Philosophie Zoologique. Lamarck noted "Olivier's Spalax, which lives underground like the mole, and is apparently exposed to daylight even less than the mole, has altogether lost the use of sight: so that it shows nothing more than vestiges of this organ."[5]
Charles Darwin was very familiar with the concept of vestigial structures, though the term for them did not yet exist. He listed a number of them in The Descent of Man, including the muscles of the ear, wisdom teeth, the appendix, the tail bone, body hair, and the semilunar fold in the corner of the eye. Darwin also noted, in On the Origin of Species, that a vestigial structure could be useless for its primary function, but still retain secondary anatomical roles: "An organ serving for two purposes, may become rudimentary or utterly aborted for one, even the more important purpose, and remain perfectly efficient for the other.... [A]n organ may become rudimentary for its proper purpose, and be used for a distinct object."[6]
In the first edition of On the Origin of Species, Darwin briefly mentioned inheritance of acquired characters under the heading "Effects of Use and Disuse", expressing little doubt that use "strengthens and enlarges certain parts, and disuse diminishes them; and that such modifications are inherited".[7] In later editions he expanded his thoughts on this,[8] and in the final chapter of the 6th edition concluded that species have been modified "