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In the context of human evolution, human vestigiality involves those traits (such as organs or behaviors) occurring in humans that have lost all or most of their original function through evolution. Although structures called ''vestigial'' often appear functionless, a vestigial structure may retain lesser functions or develop minor new ones. In some cases, structures once identified as vestigial simply had an unrecognized function. The examples of human vestigiality are numerous, including the anatomical (such as the human appendix, tailbone, wisdom teeth, and inside corner of the eye), the behavioral (goose bumps and palmar grasp reflex), sensory (decreased olfaction), and molecular (pseudogenes). Many human characteristics are also vestigial in other primates and related animals. == History == Charles Darwin listed a number of putative human vestigial features, which he termed rudimentary, in ''The Descent of Man'' (1890). These included 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 commented on the sporadic nature of many vestigial features, particularly musculature. Making reference to the work of the anatomist William Turner, Darwin highlighted a number of sporadic muscles which he identified as vestigial remnants of the panniculus carnosus particularly the sternalis muscle.〔Darwin C, ''The Descent of Man, and Selection in Relation to Sex'', London: John Murray, 1890, p.13.()〕〔Turner W, ''On the musculus sternalis'', Proc. Royal Soc. Edinburgh session 1866-1867, p.65.()〕 In 1893, Robert Wiedersheim published a book on human anatomy and its relevance to man's evolutionary history. This book contained a list of 86 human organs that he considered vestigial, or as Wiedersheim himself explained: "Organs having become wholly or in part functionless, some appearing in the Embryo alone, others present during Life constantly or inconstantly. For the greater part Organs which may be rightly termed Vestigial."〔Wiedersheim, Robert (1893). ''The Structure of Man: an index to his past history.'' London: Macmillan and Co.〕 In the 1895 edition, his wording was subtly, but significantly, different: "By such organs are meant those which were formerly of greater physiological significance than at present."〔Wiedersheim, Robert Ernst Eduard. The structure of man an index to his past history. Macmillan 1895. May be downloaded from ()〕 His list of supposedly vestigial organs included many of the examples on this page as well as others then mistakenly believed to be purely vestigial, such as the pineal gland, the thymus gland, and the pituitary gland. Some of these organs that had lost their obvious, original functions later turned out to have retained functions that had gone unrecognized before the discovery of hormones or many of the functions and tissues of the immune system.〔Muller, G. B. (2002) "Vestigial Organs and Structures." in Encyclopedia of Evolution. Mark Pagel, editor in chief, New York: Oxford University Press. pp. 1131–1133.〕 Examples included: *the role of the pineal in the regulation of the circadian rhythm (neither the function nor even the existence of melatonin was yet known); *discovery of the role of the thymus in the immune system lay many decades in the future; it remained a mystery organ until after the mid-20th century; *the pituitary and hypothalamus with their many and varied hormones were far from understood, let alone the complexity of their interrelationships. Historically, there was a trend not only to dismiss the vermiform appendix as being uselessly vestigial, but an anatomical hazard, a liability to dangerous inflammation. As late as the mid-20th century, many reputable authorities conceded it no beneficial function.〔Wells, H.g. Huxley, J. Wells, G. P. The Science of Life. Pub. Cassell 1931〕 This was a view supported, or perhaps inspired, by Darwin himself in the 1874 edition of his book The Descent of Man, and Selection in Relation to Sex. The organ's patent liability to appendicitis and its poorly understood role left the appendix open to blame for a number of possibly unrelated conditions. For example, in 1916, a surgeon claimed that removal of the appendix had cured several cases of trifacial neuralgia and other nerve pain about the head and face, even though he stated that the evidence for appendicitis in those patients was inconclusive.〔Rosenthal, M. I.: Journal of the American Medical Association, Volume 67, Issues 15-26, 1916. Page 1326〕 The discovery of hormones and hormonal principles, notably by Bayliss and Starling, argued against these views, but in the early twentieth century, there remained a great deal of fundamental research to be done on the functions of large parts of the digestive tract. In 1916, an author found it necessary to argue against the idea that the colon had no important function and that "...the ultimate disappearance of the appendix is a coordinate action and not necessarily associated with such frequent inflammations as we are witnessing in the human..."〔W. Colin MacKenzie. A Contribution to the Biology of the Vermiform Appendix. Medical record, Volume 89 Page 342 1916〕 There had been a long history of doubt about such dismissive views. Around 1920, the prominent surgeon Kenelm Hutchinson Digby documented previous observations, going back more than thirty years, that suggested lymphatic tissues, such as the tonsils and appendix, may have substantial immunological functions. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Human vestigiality」の詳細全文を読む スポンサード リンク
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