Medical conditions that cause the nasal bridge not to develop and project are also associated with epicanthic fold. Medical conditions Įpicanthic fold prevalence can sometimes be found as a sign of congenital abnormality, such as in Noonan syndrome and Zellweger syndrome. Epicanthic folds may be visible in the development stages of young children of any ethnicity, especially before the nose bridge fully develops. Many fetuses lose their epicanthic folds after three to six months of gestation. The Khoisan and some other African groups have a high frequency of the epicanthic fold. He also did not offer an explanation for the origin of epicanthic folds. He attributes the epicanthic fold to pleiotrophic genes that control for more than one characteristic or function. Frank Poirier, a physical anthropologist at Ohio State University, said that the epicanthic fold among Asian people is often explained as part of an adaptation to severe cold or tropical environments, however he suggests that neither of these explanations are sufficient to explain its presence in East and Southeast Asia, and notes that the fold can also be observed in Irish and African people. Scientific explanations include either random variation and selection (presumably sexual selection), or possible adaption to desert environment and/or high levels of ultraviolet light found in high-altitude environments, such as the Himalayas.ĭr. The exact evolutionary function and origin of epicanthic folds remains unknown. The epicanthic fold found in many African people has been tentatively linked to protection for the eye from the high levels of ultraviolet light found in desert and semi-desert areas. Though its appearance in peoples of Southeast Asia can be linked to possible descent from cold-adapted ancestors, its occurrence in various African peoples is not open to this explanation. It has also been postulated that the fold itself may provide a level of protection from snow blindness. The adipose tissue is thought to provide greater insulation for the eye and sinuses from the effects of cold, especially from freezing winds, and to represent an adaptation to cold climates. The epicanthic fold is often associated with greater levels of fat deposition around the eyeball. Its use, therefore, as a phenotypic marker to define biological populations is debatable. Also, its frequency varies clinally across Eurasia. The degree of development of the fold between individuals varies greatly, and attribution of its presence or absence is often subjective, being to a degree relative to the occurrence of the trait within the community of the specific observer. Swedish ski racer Jens Byggmark with an epicanthic fold over his left eye. Lower-frequency populations Įpicanthic folds also occur, at a considerably lower frequency, in other populations: Europeans (e.g., Scandinavians, English, Irish, Hungarians, Russians, Poles, Lithuanians, Latvians, Finns, Estonians and Samis), Jews, South Asians ( Bengalis, Sinhalese, among other groups in eastern and southern South Asia), Nilotes, Cushites, and Amazigh people. In some of these populations the trait is almost universal, specifically in East Asians and Southeast Asians, where a majority, up to 90% in some estimations, of adults have this feature. Among South Asians, they occur at very high frequencies among the Bhutanese, Northeast Indians, Kirati people and certain Adivasi tribes of eastern India. The highest frequency of occurrence of epicanthic folds is found in specific populations or ethnicities: East Asians, Southeast Asians, Central Asians, North Asians, Polynesians, Micronesians, Indigenous peoples of the Americas, Mestizos, and some African peoples (especially among Khoisan and Nilotic peoples). Įthnogeographic distribution High-frequency populations Epicanthus inversus runs from the lower eyelid skin over the medial canthus and extends to the upper lid.This is the type most often found in East Asians. Epicanthus tarsalis originates at the upper eyelid crease and merges into the skin near the medial canthus.Epicanthus palpebralis begins above the upper tarsus and extends to the inferior orbital rim. Epicanthus supraciliaris runs from the brow, curving downwards towards the lachrymal sac.Variation in the shape of the epicanthic fold has led to four types being recognised: This image highlights the epicanthic folds in a person of East Asian descent.
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