Understanding the spread of modern human populations relies on the identification of genetic markers, which are rare mutations to DNA that are passed on through generations. Different populations carry distinct markers. Once markers have been identified, they can be traced back in time to their origin — the most recent common ancestor of everyone who carries the marker. Following these markers through the generations reveals a genetic tree of many diverse branches, each of which may be followed back to where they all join — a common African root.
Human genetic variationRace and geneticsand Human genetic clustering The understanding of the genetic mechanisms underlying human skin color variation is still incomplete, however genetic studies have discovered a number of genes that affect human skin color in specific populations, and have shown that this happens independently of other physical features such as eye and hair color.
Different populations have different allele frequencies of these genes, and it is the combination of these allele variations that bring about the complex, continuous variation in skin coloration we can observe today in modern humans. Population and admixture studies suggest a 3-way model for the evolution of human skin color, with dark skin evolving in early hominids in sub-Saharan Africa and light skin evolving independently in Europe and East Asia after modern humans had expanded out of Africa.
Dark skin All modern humans share a common ancestor who lived aroundyears ago in Africa. Research shows at least 10 differences in MC1R between African and chimpanzee samples and that the gene has probably undergone a strong positive selection a selective sweep in early Hominins around 1.
Light skin For the most part, the evolution of light skin has followed different genetic paths in European and East Asian populations. They are thought to have originated after humans spread out of Africa but before the divergence of the European and Asian lineages around 30, years ago.
Studies have found two alleles in the vicinity of ASIP are associated with skin color variation in humans.
One, rs  has been identified as an indicator of skin reflectance in a forensics analysis of human phenotypes across Caucasian, African-American, South Asian, East Asian, Hispanic and Native American populations  and is about 3 times more common in non-African populations than in Africa.
A variation in TYR has also been identified as a contributor. Research indicates the selection for the light-skin alleles of these genes in Europeans is comparatively recent, having occurred later than 20, years ago and perhaps as recently as 12, to 6, years ago.
Neolithic farmers entering Europe at around the same time were intermediate, being nearly fixed for the derived SLC24A5 variant but only having the derived SLC45A2 allele in low frequencies. The SLC24A5 variant spread very rapidly throughout central and southern Europe from about 8, years ago, whereas the light skin variant of SLC45A2 spread throughout Europe after 5, years ago.
Solute carrier family 24 member 5 SLC24A5 regulates calcium in melanocytes and is important in the process of melanogenesis. It has also been shown to be one of the significant components of the skin color of modern Europeans through its PheLeu rs  allele that has been directly correlated with skin color variation in mixed-race populations.
East Asia[ edit ] A number of genes known to affect skin color have alleles that show signs of positive selection in East Asian populations. Tanning response[ edit ] Tanning response in humans is controlled by a variety of genes.
All human babies are born pale, regardless of what their adult color will be. In humans, melanin production does not peak until after puberty. In some people, the armpits become slightly darker during puberty. The interaction of genetic, hormonal, and environmental factors on skin coloration with age is still not adequately understood, but it is known that men are at their darkest baseline skin color around the age of 30, without considering the effects of tanning.
Around the same age, women experience darkening of some areas of their skin. The skin of face and hands has about twice the amount of pigment cells as unexposed areas of the body, as chronic exposure to the sun continues to stimulate melanocytes.
The blotchy appearance of skin color in the face and hands of older people is due to the uneven distribution of pigment cells and to changes in the interaction between melanocytes and keratinocytes.
Breastfeeding newborns, whose skeletons are growing, require high amounts of calcium intake from the mother's milk about 4 times more than during prenatal development part of which comes from reserves in the mother's skeleton.
Adequate vitamin D resources are needed to absorb calcium from the diet, and it has been shown that deficiencies of vitamin D and calcium increase the likelihood of various birth defects such as spina bifida and rickets.
Natural selection has led to females with lighter skin than males in all indigenous populations because women must get enough vitamin D and calcium to support the development of fetus and nursing infant and to maintain their own health.
Men and women are not born with different skin color, they begin to diverge during puberty with the influence of sex hormones. Skin may either appear lighter, or darker than normal, or lack pigmentation at all; there may be blotchy, uneven areas, patches of brown to gray discoloration or freckling.
Apart from blood-related conditions such as jaundicecarotenosisor argyriaskin pigmentation disorders generally occur because the body produces either too much or too little melanin. Depigmentation Various types of albinism are a result of genetic mutations affecting different parts of the melanin production pathway.
In a person with albinism, melanocytes can be entirely absent, or fail to produce melanin, or melanosomes can fail to mature and be transferred to keranocytes.Variations in human skin color are adaptive traits that correlate closely with geography and the sun’s ultraviolet (UV) radiation.
As early humans moved into hot, open environments in search of food and water, one big challenge was keeping cool. New gene variants reveal the evolution of human skin color. By Ann Gibbons Oct. 12, , PM.
Most people associate Africans with dark skin. I think the human population will probably end up shades of brown because there are way more brown people in the world right now than there are of any other skin colour variation. But some people think that we will evolve into two separate species altogether, and skin colour will be the least of it!
Variations in human skin color are adaptive traits that correlate closely with geography and the sun’s ultraviolet (UV) radiation.
As early humans moved into hot, open environments in search of food and water, one big challenge was keeping cool. Start studying evolution of human skin color. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Home» Human Evolution Evidence» Genetics» Human Skin Color Variation.
Human Skin Color Variation. Skin tone variation among humans. Photo courtesy of National Geographic/Sarah Leen Climate and Human Evolution.
Climate Effects on Human Evolution; Survival of the Adaptable; East African Research Projects. Olorgesailie .