Pigmentations are among the clearest examples of phenotypic variation in many species. Hair, skin and eye colors are highly heritable and visible traits in humans. Blond hair is most commonly found in Northern and Central Europeans and their descendants. Nowadays it can be found spread in many parts of the world but it is particularly frequent in North European countries and in those populated by North European explorers, traders and migrants such as United States, Australia and Canada.
There are multiple genes involved in human pigment variation. Based on genetic research it has been found that the hair color of European blonds is due to a mutation in the KITLG gene, variants in SLC24A4 gene and to at least seven variants in the gene MC1R that exist only in Europe. These multigenic determination met the criteria for genome-wide significance and gives the blond Europeans a wide range of hair shades12.
It is considered that the genetic pattern that resulted in blond hair in Europe took place about 11,000 years ago, during the last ice age. Those women with blond hair and blue eyes stand out from their rivals at a time of fierce competition for scarce males. The reason was that the main food available came from roaming herds of mammoths, reindeer, bison and horses, a dangerous task in which many males died. In addition, the cost of providing for a second wife was higher and reduced the incidence of male polygamy (polygyny), typically because women were procuring less food for themselves through food gathering. With fewer men altogether and even fewer polygynous ones, women have to compete for a limited supply of potential husbands 3 and a woman with an extraordinary aspect had some advantage. Until then, all humans had the dark hair and dark eyes that still are predominant in the rest of the world.
But Europeans are not the only population with blond hair. About a 10% of the Melanesian population in the Solomon islands combine dark skin —in fact, the darkest skin outside Africa— with bright blond afros. It was thought that those blonds were descendants of European settlers or visitors —it is occasionally called «Captain Cook’s legacy»— whereas locals have another theory, that is the result of a diet rich in fish and constant sun exposure. It seems that both hypotheses are wrong. The group of Sean Myles, a geneticist at Nova Scotia Agricultural College in Truro, Canada studied saliva and hair samples from 1,209 Solomon islanders 4. It seems that Melanesian blonds have a single-nucleotide mutation in the gen TYRP1, which codes for a protein involved in pigmentation with only one amino acid difference. The mutant gene is present in 26% of the islands’ population whereas it is absent from dark haired Solomon islanders and from 52 other populations around the world, including European countries. This explain that that percentage —10 % of the Solomon islanders carry two copies of the mutant recessive gen— and that there are no variations in the shades of blond hair, you either have blond hair or you dodn’t, contrary to Europeans. It is a real binary trait for Solomon islanders.
Thus, it is a good example of convergent evolution, where the same phenotype —blond hair— is brought by completely different mutations. It is unclear whether this Melanesian blond population had a similar sexual selection origin as it has been proposed for European blonds. In the Solomon islanders it is considered that the original population was very small and the whole Melanesia seems to have been populated by very small groups of pioneers, jumping from island to island, a situation that produced a dramatic effect in fluctuations of gene frequency 5.
- Guenther CA, Tasic B, Luo L, Bedell MA, Kingsley DM (2014) A molecular basis for classic blond hair color in Europeans. Nat Genet 46(7): 748-752. ↩
- Sulem P, Gudbjartsson DF, Stacey SN, Helgason A, Rafnar T, Magnusson KP, Manolescu A, Karason A, Palsson A, Thorleifsson G, Jakobsdottir M, Steinberg S, Pálsson S, Jonasson F, Sigurgeirsson B, Thorisdottir K, Ragnarsson R, Benediktsdottir KR, Aben KK, Kiemeney LA, Olafsson JH, Gulcher J, Kong A, Thorsteinsdottir U, Stefansson K (2007) Genetic determinants of hair, eye and skin pigmentation in Europeans. Nat Genet 39(12): 1443-1452. ↩
- Frost P (2006) European hair and eye color – A case of frequency-dependent sexual selection? Evolution and Human Behavior 27: 85-103. ↩
- Kenny EE, Timpson NJ, Sikora M, Yee MC, Moreno-Estrada A, Eng C, Huntsman S, Burchard EG, Stoneking M, Bustamante CD, Myles S (2012). Melanesian blond hair is caused by an amino acid change in TYRP1. Science 336 (6081): 554 ↩
- Loury E (2012) The Origin of Blond Afros in Melanesia. Science News. ↩