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Vestigiality describes homologous characters of organisms which have 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. All such characters can, in turn, be traced to the genes which code for such characters. Some genes no longer code for anything, and can thus be called vestigial themselves, or junk DNA. 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. 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 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]
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