The DNA of all people around the world contains a record of how living populations are related to one another, and how far back those genetic relationships go. 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.
The mitochondria inside each cell are the power stations of the body; they generate the energy necessary for cellular organisms to live and function. Mitochondria have their own DNA, abbreviated mtDNA, distinct from the DNA inside the nucleus of each cell. mtDNA is the female equivalent of a surname: it passes down from mother to offspring in every generation, and the more female offspring a mother and her female descendants produce, the more common her mtDNA type will become. But surnames mutate across many generations, and so mtDNA types have changed over the millennia. A natural mutation modifying the mtDNA in the reproductive cells of one woman will from then on characterize her descendants. These two fundamentals – inheritance along the mother line and occasional mutation – allow geneticists to reconstruct ancient genetic prehistory from the variations in mtDNA types that occur today around the world.
Population genetics often use haplogroups, which are branches on the tree of early human migrations and genetic evolution. They are defined by genetic mutations or "markers" found in molecular testing of chromosomes and mtDNA. These markers link the members of a haplogroup back to the marker's first appearance in the group's most recent common ancestor. Haplogroups often have a geographic relation.
A synthesis of mtDNA studies concluded that an early exodus out of Africa, evidenced by the remains at Skhul and Qafzeh by 135,000 to 100,000 years ago, has not left any descendants in today’s Eurasian mtDNA pool. By contrast, the successful exodus of women carrying M and N mtDNA, ancestral to all non-African mtDNA today, at around 60,000 years ago may coincide with the unprecedented low sea-levels at that time, probably opening a route across the Red Sea to Yemen. Another study of a subset of the human mtDNA sequence yielded similar results, finding that the most recent common ancestor of all the Eurasian, American, Australian, Papua New Guinean, and African lineages dates to between 73,000 and 57,000 years ago, while the average age of convergence, or coalescence time, of the three basic non-African founding haplogroups M, N, and R is 45,000 years ago.
This information has enabled scientists to develop intriguing hypotheses about when dispersals took place to different regions of the world. These hypotheses can be tested with further studies of genetics and fossils.
Modern Human Diversity - Skin Color
Why do people from different parts of the world have different colored skin? Why do people from the tropics generally have darker skin color thanthose who live in colder climates? 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. The adaptation that was favored involved an increase in the number of sweat glands on the skin while at the same time reducing the amount of body hair. With less hair, perspiration could evaporate more easily and cool the body more efficiently. But this less-hairy skin was a problem because it was exposed to a very strong sun, especially in lands near the equator. Since strong sun exposure damages the body, the solution was to evolve skin that was permanently dark so as to protect against the sun’s more damaging rays.
Melanin, the skin's brown pigment, is a natural sunscreen that protects tropical peoples from the many harmful effects of ultraviolet (UV) rays. UV rays can, for example, strip away folic acid, a nutrient essential to the development of healthy fetuses. Yet when a certain amount of UV rays penetrates the skin, it helps the human body use vitamin D to absorb the calcium necessary for strong bones. This delicate balancing act explains why the peoples that migrated to colder geographic zones with less sunlight developed lighter skin color. As people moved to areas farther from the equator with lower UV levels, natural selection favored lighter skin which allowed UV rays to penetrate and produce essential vitamin D. The darker skin of peoples who lived closer to the equator was important in preventing folate deficiency. Measures of skin reflectance, a way to quantify skin color by measuring the amount of light it reflects, in people around the world support this idea. While UV rays can cause skin cancer, because skin cancer usually affects people after they have had children, it likely had little effect on the evolution of skin color because evolution favors changes that improve reproductive success.
There is also a third factor which affects skin color: coastal peoples who eat diets rich in seafood enjoy this alternate source of vitamin D. That means that some Arctic peoples, such as native peoples of Alaska and Canada, can afford to remain dark-skinned even in low UV areas. In the summer they get high levels of UV rays reflected from the surface of snow and ice, and their dark skin protects them from this reflected light.
Modern Human Diversity - Genetics
People today look remarkably diverse on the outside. But how much of this diversity is genetically encoded? How deep are these differences between human groups? First, compared with many other mammalian species, humans are genetically far less diverse – a counterintuitive finding, given our large population and worldwide distribution. For example, the subspecies of the chimpanzee that lives just in central Africa, Pan troglodytes troglodytes, has higher levels of diversity than do humans globally, and the genetic differentiation between the western (P. t. verus) and central (P. t. troglodytes) subspecies of chimpanzees is much greater than that between human populations.
Early studies of human diversity showed that most genetic diversity was found between individuals rather than between populations or continents and that variation in human diversity is best described by geographic gradients, or clines. A wide-ranging study published in 2004 found that 87.6% percent of the total modern human genetic diversity is accounted for by the differences between individuals, and only 9.2% between continents. In general, 5%–15% of genetic variation occurs between large groups living on different continents, with the remaining majority of the variation occurring within such groups (Lewontin 1972; Jorde et al. 2000a; Hinds et al. 2005). These results show that when individuals are sampled from around the globe, the pattern seen is not a matter of discrete clusters – but rather gradients in genetic variation (gradual geographic variations in allele frequencies) that extend over the entire world. Therefore, there is no reason to assume that major genetic discontinuities exist between peoples on different continents or "races." The authors of the 2004 study say that they ‘see no reason to assume that "races" represent any units of relevance for understanding human genetic history. An exception may be genes where different selection regimes have acted in different geographical regions. However, even in those cases, the genetic discontinuities seen are generally not "racial" or continental in nature but depend on historical and cultural factors that are more local in nature’ (Serre and Pääbo 2004: 1683-1684).
Cann, R., Stoneking, M., Wilson, A., 1987. Mitochondrial DNA and human evolution. Nature 352, 31-36.
Cavalli-Sforza, L.L., Menozzi, P., Piazza, A., 1994. The History and Geography of Human Genes. Princeton University Press, Princeton, NJ.
Ebersberger, I., Metzler, D., Schwarz, C., Pääbo, S., 2002. Genomewide comparison of DNA sequences between humans and chimpanzees. American Journal of Human Genetics 70, 1490–1497.
Fischer, A., Wiebe, V., Pääbo, S., Przeworski, M., 2004. Evidence for a complex demographic history of chimpanzees. Molecular Biology and Evolution 21, 799-808.
Forster, P., 2004. Ice Ages and the mitochondrial DNA chronology of human dispersals: a review. Philosophical Transactions of the Royal Society of London B 359, 255–264.
Gonder, M.K., Mortensen, H.M., Reed, F.A., de Sousa, A., Tishkoff, S.A., 2007. Whole-mtDNA genome sequence analysis of ancient African lineages. Molecular Biology and Evolution 24, 757–768.
Hinds D.A., Stuve L.L., Nilsen G.B., Halperin E., Eskin E., Ballinger D.G., Frazer K.A., Cox D.R., 2005.Whole-genome patterns of common DNA variation in three human populations.Science307,1072–1079.
Ingman, M., Kaessmann, H., Pääbo, S., Gyllensten, U., 2000. Mitochondrial genome variation and the origin of modern humans. Nature 408, 708–713.
Ingman, M., Gyllensten, U., 2001. Analysis of the complete human mtDNA genome: methodology and inferences for human evolution. Journal of Heredity 2001:92, 454-461.
Jorde, L.B., Watkins, W.S., Bamshad, M.J., Dixon, M.E., Ricker, C.E., Seielstad, M.T., Batzer, M.A., 2000. The distribution of human genetic diversity: a comparison of mitochondrial, autosomal, and Y-chromosome data. American Journal of Human Genetics 66, 979–988.
Kaessmann, H., Heissig, F., von Haeseler, A., Pääbo, S., 1999. DNA sequence variation in a non-coding region of low recombination on the human X chromosome. Nature Genetics 22, 78-81.
Kaessmann, H., Wiebe, V., Weiss, G., Pääbo, S., 2001. Great ape DNA sequences reveal a reduced diversity and an expansion in humans. Nature Genetics 27, 155–156.
Kivisild, T., Shen, P., Wall, D.P., Do, B., Sung, R., Davis, K., Passarino, G., Underhill, P.A., Scharfe, C., Torroni, A., Scozzari, R., Modiano, D., Coppa, A., de Knijff, P., Feldman, M., Cavalli-Sforza, L.L., Oefner, P.J., 2006. The role of selection in the evolution of human mitochondrial genomes. Genetics 172, 373-387.
Lewontin, R., 1972. The apportionment of human diversity. Evolutionary Biology 6: 381-398.
Melnick, D.J., Hoelzer, G.A., 1993. What is mtDNA good for in the study of primate evolution? Evolutionary Anthropology 2, 2-10.
Serre, D., Pääbo, S., 2004. Evidence for gradients of human genetic diversity within and among continents. Genome Research 14, 1679-1685.
Tishkoff, S., Deitzsch, E., Speed, W., Pakstis, A., Kidd, J., Cheung, K., Bonne-Tamir, M., Santachiara-Benerecetti, A., Moral, P., Krings, M., Paabo, S., Watson, E., Reisch, N., Jenkins, T., Kidd, K., 1996. Global patterns of linkage disequilibrium at the CD4 locus and modern human origins. Science 271, 1380-1387.
Tishkoff, S.A., Reed, F.A., Friedlaender, F.R., Ehret, C., Ranciaro, A., Froment, A., Hirbo, J.B., Awomoyi, A.A., Bodo, J-M., Doumbo, O., Ibrahim, M., Juma, A.T., Kotze, M.J., Lema, G., Moore, J.H., Mortensen, H., Nyambo, T.B., Omar, S.A., Powell, K., Pretorius, G.S., Smith, M.W., Thera, M.A., Wambebe, C., Weber, J.L., and Williams, S.M. 2009. The genetic structure and history of Africans and African Americans. Science 324, 1035-1044.
Underhill, P.A., Shen, P., Lin, A.A., Jin, L., Passarino, G., Yang, W.H., Kauffman, E., Bonné-Tamir, B., Bertranpetit, J., Francalacci, P., Ibrahim, M., Jenkins, T., Kidd, J.R., Mehdi, S.Q., Seielstad, M.T., Wells, R.S., Piazza, A., Davis, R.W., Feldman, M.W., Cavalli-Sforza, L.L., Oefner, P.J., 2000. Y chromosome sequence variation and the history of human populations. Nature Genetics26, 358-361.
Whitfield, L., Sulston, J., Goodfellow, P., 1995. A recent common ancestry for human Y chromosomes. Nature 378, 379-380.
Genetics of Skin Color
Different populations have different frequencies of the alleles. The combined effects of the alleles bring about the complex, continuous variation in skin color in the human species worldwide.
The amount of melanin in the skin, the amount of UV exposure, genetics, the quality of melanosomes, and pigments present in the skin all play a role in racial variation. The different colors present in human skin are caused by 4 chromophores: carotenoids, hemoglobin, melanin, and oxyhemoglobin.How many human skin colors are there? ›
From pale to dark and everything in between, human skin color covers a wide range. The Pantone company, a leading authority on standardized color reproduction, has identified 110 different skin tones.Can variations in human skin color be measured? ›
Alternatively, an objective, quantitative, and observer-independent evaluation method of skin color assessment can be achieved with noninvasive devices called colorimeters and spectrophotometers. Such colorimetric devices can quantify the skin color, erythema, and tanning in various skin types.What color was the first human? ›
Color and cancer
These early humans probably had pale skin, much like humans' closest living relative, the chimpanzee, which is white under its fur. Around 1.2 million to 1.8 million years ago, early Homo sapiens evolved dark skin.
Inheritance of Skin Color
Each gene has two forms: dark skin allele (A, B, and C) and light skin allele (a, b, and c). Neither allele is completely dominant to the other, and heterozygotes exhibit an intermediate phenotype (incomplete dominance).
With aging, the outer skin layer (epidermis) thins, even though the number of cell layers remains unchanged. The number of pigment-containing cells (melanocytes) decreases. The remaining melanocytes increase in size. Aging skin looks thinner, paler, and clear (translucent).What affects skin Colour? ›
Skin color is determined by a pigment (melanin) made by specialized cells in the skin (melanocytes). The amount and type of melanin determines a person's skin color.What race was the first human? ›
The First Humans
One of the earliest known humans is Homo habilis, or “handy man,” who lived about 2.4 million to 1.4 million years ago in Eastern and Southern Africa.
As populations migrated away from the tropics into areas of low UV radiation, they developed light skin pigmentation as an evolutionary selection acting against vitamin D depletion.
A new study by Missouri School of Journalism researcher Cynthia Frisby found that people perceive a light brown skin tone to be more physically attractive than a pale or dark skin tone.When did white skin develop in humans? ›
Many scientists have believed that lighter skin gradually arose in Europeans starting around 40,000 years ago, soon after people left tropical Africa for Europe's higher latitudes.What reduces melanin? ›
You can use topical products to lighten your skin. These products reduce melanin and are commercially available. Prescription or over-the-counter skin lightening products often have the following ingredients: hydroquinone, kojic acid, vitamin C, glycolic acid, azelaic acid, retinoid.How many genes affect skin color? ›
Melanin is produced by cells called melanocytes in the skin and is the primary determinant of skin color in people with darker skin. Indeed, >150 genes have now been identified as having a direct or indirect effect on skin color.What is the oldest race in the world? ›
An unprecedented DNA study has found evidence of a single human migration out of Africa and confirmed that Aboriginal Australians are the world's oldest civilization.What is the colour of Adam? ›
God himself took dust from all four corners of the earth, and with each color (red for the blood, black for the bowels, white for the bones and veins, and green for the pale skin), created Adam.Why did humans lose their fur? ›
Humans are rare among mammals for their lack of a dense layer of protective fur or hair. And the new theory challenges widely accepted theories that humans became hairless to provide better temperature control in varied climates.Can fair parents have a dark baby? ›
How does this happen? Dear Ken, It is not uncommon for two dark skinned persons to have a light skinned baby. Skin colour is a physical characteristic that is determined by genes inherited from oneâ€™s parents.How can a fair baby get a dark father? ›
A popluar Indian belief, pineapples which is rich in Vitamin C, have said to improve the colour tone. If you want to have a fair baby, drink a glass of fresh pineapple juice once in a week. Drinking the water of the soaked fennel seeds will improve the colour of the skin.Why is dark skin beautiful? ›
Humans with dark skin pigmentation have skin naturally rich in melanin (especially eumelanin), and have more melanosomes which provide superior protection against the deleterious effects of ultraviolet radiation. This helps the body to retain its folate reserves and protects against damage to DNA.
The 4 Main Types Of Skin Tones Are:
Light. Fair. Medium. Deep (Dark)
Pale skin can be a sign that you have a shortage of normal red blood cells (anemia), which means that less oxygen is delivered to your body. This can be from a nutritional deficiency, blood loss, or a blood cancer like leukemia. Other causes of pale skin include low blood pressure or infection.What is dusky skin tone? ›
Dusky skin is a classification for a skin type that is darker than fair or wheatish skin, while still being somewhat lighter than the darker shades of brown. Dusky skin tone is also the most common skin complexion for people in India. Most probably due to our genetic heritage as well as our proximity to the equator.Why is my skin turning so dark? ›
Darker areas of skin (or an area that tans more easily) occurs when you have more melanin or overactive melanocytes. Bronzing of the skin may sometimes be mistaken for a suntan. This skin discoloration often develops slowly, starting at the elbows, knuckles, and knees and spreading from there.Does black skin get lighter with age? ›
In blacks, sun-exposed skin lightens over time whereas in whites it darkens over time.Why does skin turn dark? ›
If your body makes too much melanin, your skin gets darker. Pregnancy, Addison's disease, and sun exposure all can make your skin darker. If your body makes too little melanin, your skin gets lighter. Vitiligo is a condition that causes patches of light skin.Can I get my original skin color back? ›
You can definitely go back to your natural skin tone which over time tends to darken due to factors like dust, pollution, etc. We list tips that will lighten your skin tone by bringing back your natural shade.Why is my face darker than my body? ›
Our face skin produces more melanin compared to the rest of the body parts, so our face skin is generally a bit darker. The harmful rays of the sunlight can damage the melanin cells and as the face is more exposed to sunlight, it is the first to be impacted.Is skin color genetic? ›
Abstract. Differences in skin and hair color are principally genetically determined and are due to variation in the amount, type, and packaging of melanin polymers produced by melanocytes secreted into keratinocytes. Pigmentary phenotype is genetically complex and at a physiological level complicated.What will humans look like in 100000 years? ›
100,000 Years From Today
We will also have larger nostrils, to make breathing easier in new environments that may not be on earth. Denser hair helps to prevent heat loss from their even larger heads. Our ability to control human biology means that the man and woman of the future will have perfectly symmetrical faces.
Humans first evolved in Africa, and much of human evolution occurred on that continent. The fossils of early humans who lived between 6 and 2 million years ago come entirely from Africa. Most scientists currently recognize some 15 to 20 different species of early humans.What are the 3 human races? ›
Abstract. Using gene frequency data for 62 protein loci and 23 blood group loci, we studied the genetic relationship of the three major races of man, Caucasoid, Negroid, and Mongoloid.Why are Europeans so tall? ›
In a paper published in Nature, the researchers show that northern Europeans seem to have a stronger genetic link to a particularly tall nomadic population from the Eurasian steppe who came to Europe around 4,500 years ago. Because of these genes, northern Europeans are still tall compared to others on the continent.What nationality has olive skin? ›
Olive-toned skin is especially apparent among people from Iran, Lebanon, and Algeria. Other Middle Eastern countries with ethnicities that have olive skin tone include Egypt, Turkey, and Afghanistan.How did the first humans look like? ›
With the exception of Neanderthals, they had smaller skulls than we did. And those skulls were often more of an oblong than a sphere like ours is, with broad noses and large nostrils. Most ancient humans had jaws that were considerably more robust than ours, too, likely a reflection of their hardy diets.Which country has beautiful skin? ›
People in countries like Denmark, Finland, and Norway tend to look at beauty as deeper than what you put on your skin.How do I know my true skin color? ›
In natural light, check the appearance of your veins beneath your skin. If your veins appear blue or purple, you have a cool skin tone. If your veins look green or a greenish blue, you have a warm skin tone. If you can't tell whether or not your veins are green or blue, you probably have a neutral skin tone.Who has the most beautiful skin in the world? ›
- Kim Kardashian. She has the type of creamy skin complexion that makes people jealous. ...
- Nicole Kidman. Kidman may be one of the best role models in Hollywood for judicious use of sunscreen. ...
- Jennifer Aniston. ...
- Natalie Portman. ...
- Beyonce Knowles.
As you can either have one blood group or another, this is discontinuous variation. Some other examples of discontinuous variation: Hair colour. Gender.How is skin color in humans determined? ›
Abstract. Differences in skin and hair color are principally genetically determined and are due to variation in the amount, type, and packaging of melanin polymers produced by melanocytes secreted into keratinocytes. Pigmentary phenotype is genetically complex and at a physiological level complicated.
Which of the following statements apply to the variation in human skin color? Human skin color variation is primarily determined by the type and amount of melanin pigment in the skin. Human skin color variation evolved recently in hominid evolution, once some populations of our human ancestors migrated out of Africa.Why is there a wide variation in skin color in humans quizlet? ›
Why is there a wide variation in skin color in humans? Skin color is a polygenic trait.Is eye colour discontinuous? ›
Discontinuous: Eye colour, handedness & lobed/lobeless ears. Continuous: Hand span, arm length & height.What are 2 types of variation? ›
Genetic variation - these are differences between individuals that are inherited from parents, such as the colour of your eyes, hair and skin. Environmental variation - these are differences between individuals that are not inherited but caused by the environment that the organism lives in, including scars and tattoos.What type of variation is eye colour? ›
In the most elementary form, the inheritance of eye color is classified as a Mendelian trait. On the basis of the observation of more than two phenotypes, eye color has a more complex pattern of inheritance. Eye color ranges include varying shades of brown, hazel, green, blue, gray, and in rare cases, violet and red.Which skin tone is most attractive? ›
A new study by Missouri School of Journalism researcher Cynthia Frisby found that people perceive a light brown skin tone to be more physically attractive than a pale or dark skin tone.Why is my skin turning so dark? ›
Darker areas of skin (or an area that tans more easily) occurs when you have more melanin or overactive melanocytes. Bronzing of the skin may sometimes be mistaken for a suntan. This skin discoloration often develops slowly, starting at the elbows, knuckles, and knees and spreading from there.When did white skin develop in humans? ›
Many scientists have believed that lighter skin gradually arose in Europeans starting around 40,000 years ago, soon after people left tropical Africa for Europe's higher latitudes.Which three of the following factors can affect skin color? ›
There are three main physiological factors that affect skin color - the state of the blood vessels, oxygenation of the blood, and diet.What is true melanin? ›
Melanin is a type of pigment that gives color to the hair, skin, and eyes in humans and animals. In addition to providing pigmentation for the cells, melanin also absorbs harmful UV rays and protects against cellular damage from UV light exposure.
Background: Skin color is a well-recognized adaptive trait and has been studied extensively in humans. Understanding the genetic basis of adaptation of skin color in various populations has many implications in human evolution and medicine.Is skin color a polygenic trait? ›
A polygenic trait is a characteristic, such as height or skin color, that is influenced by two or more genes. Because multiple genes are involved, polygenic traits do not follow the patterns of Mendelian inheritance. Many polygenic traits are also influenced by the environment and are called multifactorial.Are freckles dominant or recessive traits? ›
Freckling is a recessive trait, so both parents have to be carriers and pass the tendency on for it to show up, says Amit Sharma, M.D., a dermatologist at the Mayo Clinic, who researches dermatologic genetics. The so-called gene for freckling is actually a benign mutation of the MC1R gene, which regulates pigment.Which is a phenotype? ›
Phenotype refers to an individual's observable traits, such as height, eye color and blood type. A person's phenotype is determined by both their genomic makeup (genotype) and environmental factors.