In human anatomy, this is the fold of skin covering the inner corner () of the eye , normally from the top of the eye downward in a semilunar form. The epicanthic (or epicanthal) fold is a normal feature of fetuses of all races but is present in a pronounced form and in high concentrations in humans of certain geographic races and subraces. The epicanthic fold is sometimes referred to as the ‘Mongolian eye fold’, because of its high incidence in and historical association with the Mongoloid (Asian) geographic race. The presence or absence of the epicanthus, which helps produce in Asians a distinctive eye shape and facial appearance, has helped fuel controversies in physical anthropology and evolutionary theory, including historical attempts to establish racial hierarchies based on evolutionary fitness and disputes concerning the nature of evolutionary adaptation. In addition, epicanthic folds in individuals of groups without a high normal incidence of its presence is often phenotypic of genetic or congenital disorders. In some recent debates, the alleged absence of the fold in some depictions and descriptions of humans from Chinese and Indian history has led some Afrocentric historians to claim an African origin of at least some aspects of Indian and Shang dynasty Chinese culture.In addition to Asians and eastern subarctic and arctic Eurasians, some native American peoples (especially those of Middle America and some populations in South American lowland areas), the Capoid local race of southern Africa, and some of the composite racial groups of Pacific island peoples have high incidence of developed epicanthic folds. The fold occurs less frequently in Southeast Asian populations and in North American Indian groups but occurs occasionally in some European groups, for example in some Scandinavians and Poles.While epicanthic folds occur more frequently in Asiatic groups and those peoples genetically linked to Asia , its presence is not universal in these peoples and it occurs less frequently in other groups. The incidence of epicanthic folds varies widely among the nine major geographic races and their local races. Attempts to define racial groups by the presence or absence of such features, by phenotype, rather than by genotype and specific inherited traits, are historically problematic and scientifically unreliable. There is substantial variation in phenotype within geographic races and subraces produced by the gene flow inevitable in an aggressively mobile species such as our own, by environmental conditions, and simply by individual variation due to a number of causes, including genetic mutation and the ‘small-sample’ effects of isolated population groups. Modern genetics rejects the notion of a ‘pure’ race; while the historical origins of some geographic groups are obscure, contemporary racial groups are mixtures of the gene pools of many geographic races. Thus, the presence or absence of a developed epicanthic fold, while an indication of one of a number of genetic origins and an important diagnostic feature of certain genetic disorders, cannot bear the cultural freight often bequeathed to it by history, pseudo-science, and prejudice.The association of the epicanthic fold with Mongolians and Asians more generally served to reinforce notions of racial and cultural supremacy in nineteenth and early-to-mid twentieth century European physical anthropology physiognomy , and racial theory. Humans with the genetic anomaly now known as Down's syndrome, caused by having three copies (trisomy) of chromosome 21, have limited physical growth and mental retardation of varying severity, and an increased risk of other serious physical problems. Down's syndrome is one of the more common chromosomal defects, occurring on average in 1 in 900 live births. The Down's syndrome infant is quickly recognized by both facial and more general cranial characteristics, including a rounded head, short neck, thin and usually fine hair, flat nose, small mouth, and, especially, slanting eyes with pronounced epicanthic folds.John Langdon Haydon Down first described this syndrome in 1866 and termed it ‘mongolism’ because of the eyefold and other facial features that Down believed linked the European children he observed to geographic races with a high incidence of such features, including the Asian geographic race (of which the Mongolian people constitute a local race). Down's report on this condition is an important example of the influence of cultural assumptions both on reading facial features and on the construction of anthropological theories designed to categorize and judge peoples: his comparison of European children born with a chromosomal disorder with the normal features of many Mongolians was both scientifically inaccurate as an analysis of the condition and a patronizing mischaracterization of Mongolians. Down argued that these children represented a degeneration of the superior (European) human type, stating that ‘A very large number of congenital idiots are typical Mongols .’ The racial theories used by Down and others have been decisively rejected by modern science, but it is only recently that the descriptions of Down's syndrome as ‘mongolism’ or ‘mongolian idiocy’ and persons with Down's syndrome as ‘ mongols ’ or ‘mongolian idiots’ have begun to fade from view.In addition to Down's syndrome, epicanthic folds occur in other, less common genetic disorders, including Trigonocephaly ‘C’ syndrome and two types of ‘Blepharophimosis, Ptosis, Epicanthus Inversus Syndrome’ (BPES). In the latter condition, the epicanthic fold is inverted, extending from the lower eyelid up the side of the nose. Folds also occur in certain congenital conditions, including fetal alcohol syndrome . While the facial anomalies of infants with fetal alcohol syndrome are usually less pronounced than those of a Down's syndrome child, some of the same features occur, including a flat nose and nasal bridge, and developed epicanthic folds.

Jeffrey H. Barker