Light skin

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.

[12] 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.

[13] 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[14] evolved to have light skin pigmentation.

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".

[27] Summarising these studies, Hanel and Carlberg (2020) 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.

[23] This is consistent with Jones et al. (2015), 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.

[28] However, a coalescent analysis of this allele by Crawford et al. (2017) gave a more narrowly constrained, and earlier, split date of ~29,000 years ago (with a 95% confidence window from 28,000 to 31,000 bp).

[31] A further wave of lighter-skinned populations across Europe (and elsewhere) is associated with the Yamnaya culture and the Indo-European migrations bearing Ancient North Eurasian ancestry and the KITLG allele for blond hair.

[32] Huang et al. (2021) found the existence of "selective pressure on light pigmentation in the ancestral population of Europeans and East Asians", prior to their divergence from each other.

[37] Crawford et al. (2017) similarly found evidence for selection towards light pigmentation prior to the divergence of West Eurasians and East Asians.

"[39] 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 (WHG).

[42] 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.

[23] Bagnasco, G et al. (2024), 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.

[43] In 2015, it was discovered that 13,000 year old samples of Caucasus Hunter Gatherers (CHG) from Georgia carried the mutation and derived alleles for very fair skinned pigmentation similar to Early Farmers (EF).

This trait was said to have a relatively long history in Eurasia and risen to high frequency during the Neolithic expansion, with its origin probably predating the Last Glacial Maximum (LGM).

[46][47] A research paper in 2017 indicated Egyptians at Abusir el-Meleq from 2,590 to 2,023 years ago, had a derived variant for the SLC24A5 locus, which contributes to lighter skin pigmentation, and was shown to be at high frequency in Neolithic Anatolia, accordant with the sample's ancestral affinities.

[49] In the same year, according to phenotype SNP analysis, the precolonial Guanche inhabitants of the Canary Islands were showing consistent traits such as light and medium skin, with dark hair and brown eyes.

[50] A paper conducted by Fregel, Rosa et al. (2018) showed that in North Africa, Late Neolithic Moroccans had the European/Caucasus derived SLC24A5 mutation and other alleles and genes that predispose individuals to lighter skin and eye colours.

[52][53][54][55][56] In 1998, anthropologist Nina Jablonski and her husband George Chaplin collected spectrometer data to measure UV radiation levels around the world and compared it to published information on the skin colour of indigenous populations of more than 50 countries.

She suggests that people living far from the equator developed light skin to produce adequate amounts of vitamin D during winter with low levels of UV radiation.

[63] Some people of the polar regions, like the Inuit (Eskimos), retained their dark skin; they ate Vitamin D-rich seafood, such as fish and sea mammal blubber.

As their founding populations lacked alleles for light skin colour, they may have had insufficient time for significantly lower melanin production to have been selected for by nature after being introduced by random mutations.

Additionally, in the spring, Inuit would receive high levels of UV radiation as reflection from the snow, and their relatively darker skin then protects them from the sunlight.

The subsequent spread of light skin was thought to be caused by assortive mating[68] and sexual selection contributed to an even lighter pigmentation in females.

Humans with naturally occurring light skin have varied amounts of smaller and sparsely distributed eumelanin and its lighter-coloured relative, pheomelanin.

The colour associated with the circulating haemoglobin becomes more obvious, especially in the face, when arterioles dilate and become tumefied with blood as a result of prolonged physical exercise or stimulation of the sympathetic nervous system (usually embarrassment or anger).

[96][97] The strongly red appearance of lightly pigmented skin as a response to high UV radiation levels is caused by the increased diameter, number, and blood flow of the capillaries.

Heavy tanning does not approach the photoprotective effect against UVR-induced DNA damage compared to naturally occurring dark skin,[98][99] however it offers great protection against seasonal variations in UVR.

Vitamin D promotes the production of cathelicidin, which helps to defend humans' bodies against fungal, bacterial, and viral infections, including flu.