Light skin
Light skin is a human skin color that has a low level of eumelanin pigmentation as an adaptation to environments of low UV radiation.
Due to migrations of people in recent centuries, light-skinned populations today are found all over the world. Light skin is most commonly found amongst the native populations of Europe, East Asia, West Asia, Central Asia, South Asia, Siberia, and North Africa as measured through skin reflectance. People with light skin pigmentation are often referred to as "white", but the majority of countries officially categorize people by ethnic or national origin and not by perceived skin tone. Furthermore, definitions and perceptions of "ethnicity" or "race" vary greatly from country to country.
Humans with light skin pigmentation have skin with low amounts of eumelanin, and possess fewer melanosomes than humans with dark skin pigmentation. Light skin provides better absorption qualities of ultraviolet radiation, which helps the body to synthesize higher amounts of vitamin D for bodily processes such as calcium development. On the other hand, light-skinned people who live near the equator, where there is abundant sunlight, are at an increased risk of folate depletion. As a consequence of folate depletion, they are at a higher risk of DNA damage, birth defects, and numerous types of cancers, especially skin cancer. Humans with darker skin who live further from the tropics may have lower vitamin D levels, which can also lead to health complications, both physical and mental, including miscarriage and a greater risk of developing schizophrenia. These two observations form the "vitamin D–folate hypothesis", which attempts to explain why populations that migrated away from the tropics into areas of low UV radiation evolved to have light skin pigmentation.
The distribution of light-skinned populations is highly correlated with the low ultraviolet radiation levels of the regions inhabited by them. Historically, light-skinned populations almost exclusively lived far from the equator, in high latitude areas with low sunlight intensity.
Evolution
It is generally accepted that dark skin evolved as a protection against the effect of UV radiation; eumelanin protects against both folate depletion and direct damage to DNA. This accounts for the dark skin pigmentation of Homo sapiens during their development in Africa; the major migrations out of Africa to colonize the rest of the world were also dark-skinned. It is widely supposed that light skin pigmentation developed due to the importance of maintaining vitamin D3 production in the skin. Strong selective pressure would be expected for the evolution of light skin in areas of low UV radiation.After the ancestors of West Eurasians and East Eurasians diverged more than 40,000 years ago, lighter skin tones evolved independently in a subset of each of the two populations. In West Eurasians, the A111T allele of the rs1426654 polymorphism in the pigmentation gene SLC24A5 has the largest skin lightening effect and is widespread in Europe, South Asia, Central Asia, the Near East and North Africa.
In a 2013 study, Canfield et al. established that SLC24A5 sits in a block of haplotypes, one of which is shared by virtually all chromosomes that bear the A111T variant. This "equivalence" between C11 and A111T indicates that all people who carry this skin-lightening allele descend from a common origin: a single carrier who lived most likely "between the Middle East and the Indian subcontinent". Canfield et al. attempted to date the A111T mutation but only constrained the age range to before the Neolithic. However, a second study from the same year estimated the coalescent age for this allele to between ~28,000 and ~22,000 years ago.
The second most important skin-lightening factor in West Eurasians is the depigmenting allele F374 of the rs16891982 polymorphism located in the melanin-synthesis gene SLC45A2. From its low haplotype diversity, Yuasa et al. likewise concluded that this mutation "occurred only once in the ancestry of Caucasians".
Summarizing these studies, Hanel and Carlberg decided that the alleles of the two genes SLC24A5 and SLC45A2 which are most associated with lighter skin colour in modern Europeans originated in West Asia about 22,000 to 28,000 years ago and these two mutations each arose in a single carrier. This is consistent with Jones et al., who reconstructed the relationship between Near Eastern Neolithic farmers and Caucasus Hunter-Gatherers: two populations which carried the light skin variant of SLC24A5. Analysing newly sequenced ancient genomes, Jones et al. estimated the split date at ~24,000 bp and localised the separation to somewhere south of the Caucasus. However, a coalescent analysis of this allele by Crawford et al. gave a more narrowly constrained, and earlier, split date of ~29,000 years ago.
The light skin variants of SLC24A5 and SLC45A2 were present in Anatolia by 9,000 years ago, where they became associated with the Neolithic Revolution. From here, their carriers spread Neolithic farming across Europe. Lighter skin and blond hair also evolved in the Ancient North Eurasian population.
A further wave of lighter-skinned populations across Europe is associated with the Yamnaya culture and the Indo-European migrations bearing Ancient North Eurasian ancestry and the KITLG allele for blond hair. Furthermore, the SLC24A5 gene linked with light pigmentation in Europeans was introduced into East Africa from Europe over five thousand years ago. These alleles can now be found in the San, Ethiopians, and Tanzanian populations with Afro-Asiatic ancestry. The SLC24A5 in Ethiopia maintains a substantial frequency with Semitic and Cushitic speaking populations, compared with Omotic, Nilotic or Niger-Congo speaking groups. It is inferred that it may have arrived into the region via migration from the Levant, which is also supported by linguistic evidence. In the San people, it was acquired from interactions with Eastern African pastoralists. Meanwhile, in the case of East Asia and the Americas, a variation of the MFSD12 gene is responsible for lighter skin colour. The modern association between skin tone and latitude is thus a relatively recent development.
According to Crawford et al., most of the genetic variants associated with light and dark pigmentation appear to have originated more than 300,000 years ago. African, South Asian and Australo-Melanesian populations also carry derived alleles for dark skin pigmentation that are not found in Europeans or East Asians. Huang et al. found the existence of "selective pressure on light pigmentation in the ancestral population of Europeans and East Asians", prior to the divergence of their ancestors. Skin pigmentation was also found to be affected by directional selection towards darker skin among Africans, as well as lighter skin among Eurasians. Crawford et al. found evidence for the emergence of alleles associated with lighter and darker pigmentation prior to the origin of modern humans at c. 300kya.
The predominance of lighter skin among East Asians can be traced back to the positive selection for the rs1800414-G allele thought to date back to the Late Palaeolithic period, following the northward migration of modern humans from South/Southeast Asia. This allele is distinct from that observed among West Eurasians.
The A111T mutation in the SLC24A5 gene predominates in populations with Western Eurasian ancestry. The geographical distribution shows that it is nearly fixed in all of Europe and most of the Middle East, extending east to some populations in present-day Pakistan and Northern India. It shows a latitudinal decline toward the Equator, with high frequencies in North Africa, and intermediate in Ethiopia and Somalia.
Ancient Populations
Some authors have expressed caution regarding the skin pigmentation SNP predictions in early Paleolithic groups. According to Ju et al. : "Relatively dark skin pigmentation in Early Upper Paleolithic Europe would be consistent with those populations being relatively poorly adapted to high-latitude conditions as a result of having recently migrated from lower latitudes. On the other hand, although we have shown that these populations carried few of the light pigmentation alleles that are segregating in present-day Europe, they may have carried different alleles that we cannot now detect. As an extreme example, Neanderthals and the Altai Denisovan individual show genetic scores that are in a similar range to Early Upper Paleolithic individuals, but it is highly plausible that these populations, who lived at high latitudes for hundreds of thousands of years, would have adapted independently to low UV levels. For this reason, we cannot confidently make statements about the skin pigmentation of ancient populations."Research in 2022 inferred that the use of an "intermediate" skin tone phenotype, are for those commonly found in present-day Southern European and Mediterranean populations, as opposed to "pale" ones in present-day Northern Europeans.
Europe
A study from 2015 found that genes contributing to fair skin were nearly fixed in the Anatolian Neolithic Farmers: "The second strongest signal in our analysis is at the derived allele of rs16891982 in SLC45A2, which contributes to light skin pigmentation and is almost fixed in present-day Europeans but occurred at much lower frequency in ancient populations. In contrast, the derived allele of SLC24A5 that is the other major determinant of light skin pigmentation in modern Europe appears fixed in the Anatolian Neolithic, suggesting that its rapid increase in frequency to around 0.9 in Early Neolithic Europe was mostly due to migration."In 2018, a study was released showing many late Mesolithic Scandinavians from 9,500 years ago in Northern Europe had blonde hair and light skin, which was in contrast to some of their contemporaries, the darker Western Hunter Gatherers. However, a 2024 paper found that phenotypically most of their studied WHG individuals carried the dark skin and blue eyes characteristic of WHGs, but some other WHGs in France they sequenced also had pale to intermediate skin pigmentation. Another entry in 2018, showed that the Eastern Hunter Gatherers, Scandinavian Hunter Gatherers, and the Baltic foragers, all had the derived alleles for light skin pigmentation.
The Western Steppe Herders, an early Bronze Age population are believed to have also contributed to the skin and hair pigmentation in Europe, having a dominant effect on the phenotypes of Northern Europeans in particular.
Bagnasco, G et al., discovered that the phenotypic traits for a group of Etruscans from 3,000 to 2,700 years ago showed a population with blue-eyes, light to dark brown hair, and pale white to intermediate skin tones.
In 2025 a downsampling experiment attempted to gauge phenotypes of ancient Europeans across many regions using low coverage methods. They found that for skin traits in the Palaeolithic, the Russian Kostenki 14 was the only one to exhibit an intermediate skin colour, with the remainder having dark phenotypes. During the Mesolithic, there was more variability with 7 samples being intermediate, and 3 being pale. The Neolithic showed 25 intermediate and 5 pale. Copper-Age had 7 intermediate and 4 pale. The Bronze-Age had 15 intermediate and 6 pale. Lastly, the Iron-Age had 6 intermediate and 2 pale samples. They highlighted some caution with using this imputational approach at such low coverage using HIrisPlex-S.