question: Why people on different regions have different facial features?
comment: Sometimes it's caused by the environment, and sometimes it's just random mutations that don't actually do much to help the human survive. In either case, if those mutations are the type that kids will always inherit (a "dominant" one), they can take over a population over time. For stuff that's caused by the environment, eyes that are inset deeply and are horizontally compact can help a person see in areas of bright glare and high levels of sunlight such as Arctic ice fields, Mongolian steppes or Tibetan mountains. So someone with a mutation that got those sort of eyes was better equipped to spot danger or hunt in those environments, and it became a regional trend if they passed it on to their kids every time for a few generations. On the other hand, larger rounder eyes might be better suited for low lighting areas such as jungle where you didn't have to worry so much about glare or sunburn. And larger nostrils make breathing easier when running long distances to catch prey animals on the open savannah, but smaller noses got frostbitten less in areas of extreme cold. And there's lots of accidental stuff, like red eyebrows, that can get passed on simply because it's dominant even though it doesn't offer much to help the person grow old enough to have a lot of kids. A lot of genetics is quite simply random.
passages: Variation in craniofacial form between humans has been found to be largely due to differing patterns of biological inheritance. Modern cross-analysis of osteological variables and genome-wide SNPs has identified specific genes, which control this craniofacial development. Of these genes, DCHS2, RUNX2, GLI3, PAX1 and PAX3 were found to determine nasal morphology, whereas EDAR impacts chin protrusion and facial hair, both of which have been recently selected in Caucasians
  
  Section::::Racial anthropology.:Cold tolerance.
   The distribution of many physical traits resembles the distribution of genetic variation within and between human populations (American Association of Physical Anthropologists 1996; Keita and Kittles 1997). For example, ~90% of the variation in human head shapes occurs within continental groups, and ~10% separates groups, with a greater variability of head shape among individuals with recent African ancestors (Relethford 2002).
   Neves' conclusions have been challenged researchers who argued that the cranio-facial variability could just be due to genetic drift and other factors affecting cranio-facial plasticity in Native Americans.
   Section::::History and geographic distribution.:Distribution of variation.:Phenotypic variation.
  
  Sub-Saharan Africa has the most human genetic diversity and the same has been shown to hold true for phenotypic variation in skull form. Phenotype is connected to genotype through gene expression. Genetic diversity decreases smoothly with migratory distance from that region, which many scientists believe to be the origin of modern humans, and that decrease is mirrored by a decrease in phenotypic variation. Skull measurements are an example of a physical attribute whose within-population variation decreases with distance from Africa.
   In terms of facial features, Hiernaux (1975) observed that the nasal profile most common amongst Nilotic populations is broad, with characteristically high index values ranging from 86.9 to 92.0. He also reported that lower nasal indices are often found amongst Nilotes who inhabit the more southerly Great Lakes region, such as the Maasai, a fact which he attributed to genetic differences.
   Section::::History and geographic distribution.:Population genetics.
  
  Because of the common ancestry of all humans, only a small number of variants have large differences in frequency between populations. However, some rare variants in the world's human population are much more frequent in at least one population (more than 5%).
   taxonomic status for it". Critics of multiregionalism have pointed out that no single human trait is unique to a geographical region (i.e. confined to one population and not found in any other) but Wolpoff "et al". (2000) note that regional continuity only recognizes combinations of features, not traits if individually accessed, a point they elsewhere compare to the forensic identification of a human skeleton:
   Understanding how genetic diversity in the human population impacts various levels of gene expression is an active area of research. While earlier studies focused on the relationship between DNA variation and RNA expression, more recent efforts are characterizing the genetic control of various aspects of gene expression including chromatin states, translation, and protein levels. A study published in 2007 found that 25% of genes showed different levels of gene expression between populations of European and Asian descent. The primary cause of this difference in gene expression was thought to be SNPs in gene regulatory regions of DNA. Another study published in 2007 found that approximately 83% of genes were expressed at different levels among individuals and about 17% between populations of European and African descent.
   The muscles of the face play a prominent role in the expression of emotion, and vary among different individuals, giving rise to additional diversity in expression and facial features.
   Richard Jantz and Lee Meadows Jantz who are both directors at the Forensic Anthropology Center at the University of Tennessee said white American skulls of both sexes have become less neotenous since the mid-19th century.
  
  Section::::Between races, ethnicities and among primates.:Aboriginal Australians.
  
  Frederick S. Hulse wrote in 1962 that aboriginal Australians have retained "similar" "skeletal characteristics" to those "which most men possessed in earlier times" (gerontomorphic characteristics) that are "contrary" to the "pedomorphic qualities" which the Bushmen have evolved.
  
  Section::::Between races, ethnicities and among primates.:Mongoloids.
   In humans, the main cause is genetic drift. Serial founder effects and past small population size (increasing the likelihood of genetic drift) may have had an important influence in neutral differences between populations. The second main cause of genetic variation is due to the high degree of neutrality of most mutations. A small, but significant number of genes appear to have undergone recent natural selection, and these selective pressures are sometimes specific to one region.
  
  Section::::Measures of variation.
   Combinations of features are "unique" in the sense of being found in only one region, or more weakly limited to one region at high frequency (very rarely in another). Wolpoff stresses that regional continuity works in conjunction with genetic exchanges between populations. Long-term regional continuity in certain morphological traits is explained by Alan Thorne's "Centre and Edge" population genetics model which resolves Weidenreich's paradox of "how did populations retain geographical distinctions and yet evolve together?". For example, in 2001 Wolpoff and colleagues published an analysis of character traits of the skulls of early modern human fossils in Australia and central Europe. They concluded that the diversity of these recent humans could not "result exclusively from a single late Pleistocene dispersal", and implied dual ancestry for each region, involving interbreeding with Africans.
   Some developmental disorders are associated with an increased likelihood that the person will have difficulties in face perception, notably autism spectrum disorder and nonverbal learning disorder.
  
  Section::::Cause.
   In the case of Chile,"The use of mitochondrial DNA and Y chromosome" test results show the following: The European component is predominant (91.0%, versus 9.0% of the aboriginal one) in the Chilean upper class, the middle classes, 66.8%-62.3% European component and 37.7%-33.2 of mixed aboriginal and lower classes at 55%-52.9% European component and 47.1%-45% mix of Aboriginal.
   Geographical distribution of human variation is complex and constantly shifts through time which reflects complicated human evolutionary history. Most human biological variation is clinally distributed and blends gradually from one area to the next. Groups of people around the world have different frequencies of polymorphic genes. Furthermore, different traits are non-concordant and each have different clinal distribution. Adaptability varies both from person to person and from population to population. The most efficient adaptive responses are found in geographical populations where the environmental stimuli are the strongest (e.g. Tibetans are highly adapted to high altitudes). The clinal geographic genetic variation is further complicated by the migration and mixing between human populations which has been occurring since prehistoric times.
   The evolutionary forces that contribute to patterns of human genetic variation include new mutations, natural selection, sexual selection, genetic drift, population bottlenecks, founder effects, isolation by distance, genetic admixture and barriers to gene flow. The most influential factors affecting human genetic variation are founder effects and isolation by distance.
   There are at least three reasons why genetic variation exists between populations. Natural selection may confer an adaptive advantage to individuals in a specific environment if an allele provides a competitive advantage. Alleles under selection are likely to occur only in those geographic regions where they confer an advantage. A second important process is genetic drift, which is the effect of random changes in the gene pool, under conditions where most mutations are neutral (that is, they do not appear to have any positive or negative selective effect on the organism). Finally, small migrant populations have statistical differences—call the founder effect—from the overall populations where they originated; when these migrants settle new areas, their descendant population typically differs from their population of origin: different genes predominate and it is less genetically diverse.
   The highest frequency of occurrence of epicanthic folds is found in specific ethnicities: East Asians, Southeast Asians, Central Asians, North Asians, Polynesians, Micronesians, Native Americans (as well as Mestizos), the Khoisan, and the Malagasy. 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.
  
  Section::::Factors.:Ethnicity and geographic distribution.:Lower frequency populations.
   Section::::Theoretical approaches.:Race-feature theory.
  
  In his 1996 study, researchers noticed that when looking at ethnicity, in-group faces are processed without acknowledgement of ethnic-specific details and features. People code faces that deviate from the norm of their ethnic group through the absence or presence of distinctive ethnic features.
   In the case of people, the accentuation effect is similar to stereotyping and social categorization in that when classified as part of a group, people's features seem to more closely match their classification rather than any individual differences they have.
  
  Section::::Within ethnicity and faces.
   Section::::Early history.
   Humans have a high interindividual variation in pseudogenes and OR genes which research attributes to geographical and cultural separation. Selection and cultural practices can conserve OR genes even though it is likely caused by bottleneck effects and geographic isolation.
   Leonard Halford Dudley Buxton who taught physical anthropology at Oxford University said that in Asians the depression of the nose is below the nasion rather than at the place where the nasal bones meet the frontal bone like in the "European races". Buxton said that the Mongoloid nasal bones form a wider angle rather than the narrower angle of the "European races". Buxton said that these features of the nose of the Mongoloid make it "flatter" and "not unlike that found in European children". Buxton said that Mongoloids have the "Mongolian fold", and this "fold occurs occasionally in European children, and sometimes even in adults". 
   The other major factor contributing to patterns of human genetic variation is "isolation by distance". According to this model, populations that live near one another are more likely to exchange mates than populations that live farther apart. As a result, populations that live near one another are genetically more similar than populations that live far apart.
   Blackfoot disease is a disease caused by environmental pollution and causes people to have black, charcoal-like skin in the lower limbs. This is caused by arsenic pollution in water and food source. This is an example of how disease can affect human variation. Another disease that can affect human variation is syphilis, a sexual transmitted disease. Syphilis does not affect human variation until the middle stage of the disease. It then starts to grow rashes all over the body, affecting people's human variation.
  
  Section::::Environmental factors.:Nutrition.
  