Who do you look like?

When a new baby arrives, relatives love to spot resemblances. She has her father's eyes, her mother's mouth, grandmother's nose and so on. So it seems logical, when trying to guess more distant ancestry, to home in on appearances. If you read that the Vikings were tall and blond, and you are short and dark, you feel that you can rule out any Vikings in your ancestry. But is it that simple? Suppose you have one tall, fair-haired great-grand-parent and seven who were short and dark. Would you expect to be tall and blond? The opposite situation can be even more confusing. Two parents with dark hair and eyes can produce a blond, blue-eyed baby, if they both had such an ancestor and passed down his or her genes to the baby. Suppose that baby was adopted. He or she might imagine a long line of blond only ancestors. Looks can lead you astray.

Traits such as height, facial features and colouring are inherited autosomally. That means that the code for them is found on the 22 pairs of chromosomes that males and females share. (The other pair is two X-chromosomes for a woman, and an X and a Y for a man.) Genetic coding from both parents recombines into a new set of chromosomes for a new baby. The University of California: Berkeley provides a quick, animated guide to Sex and Genetic Shuffling: The Details. Because of the re-mixing in every generation of autosomal inheritance, it is too complicated to use in tracking human migration. That is why population geneticists use mitochondrial DNA, which passes down unchanged from mother to child, and Y-DNA, which passes unchanged from father to son, except for the occasional spontaneous mutation in both cases. These haplogroups have nothing to do with the inheritance of height, or colouring or other traits.1M.Jobling, M.E. Hules and C. Tyler-Smith, Human Evolutionary Genetics (2004), chapter 2.

Pigmentation

Distribution of light hairDistribution of eye colourColouring leaps to mind when Europeans think about appearances. Whereas most of the peoples of the planet have uniformly black hair and dark eyes, people with origins in Europe, Western Asia and North Africa have a wider range of colouring. Why is that? Dark skin protects people from ultra-violet light, but may make it more difficult for their skin to synthesise vitamin D, essential for bone growth and activation of the immune system. Pale people in sunny places are at higher risk of skin cancer and folate deficiency, while dark people in cooler climes are prone to problems of low vitamin D. So it has long been supposed that the range of skin colours we see today arose through natural selection.2M.Jobling, M.E. Hules and C. Tyler-Smith, Human Evolutionary Genetics (2004), section 13.3 and box 13.4 provide an introduction to the subject, updated by A. Juzeniene et al., Development of different human skin colors: A review highlighting photobiological and photobiophysical aspects, Journal of Photochemistry and Photobiology B: Biology, vol. 96, no. 2 (3 August 2009), pp. 93-100; M. Rode von Essen et al, Vitamin D controls T cell antigen receptor signaling and activation of human T cells, Nature Immunology (online ahead of print 7 March 2010).

How does that work? Since our genes code for functions, a mutation generally results in loss of function. The code has become faulty. So it is with the mutations that cause paler colouring. Mutations in specific genes prevent the body from producing melanin - the most important pigment influencing skin and hair colour. In places drenched in ultra-violet light, such mutations would be a disadvantage. People carrying them could die before they had a chance to reproduce at all. Or they could have fewer surviving offspring. But in cloudier climes such mutations give their bearers an advantage, so gradually they would gain ground in a population there.

Interestingly it seems that the Neanderthals could have been ahead of us in developing pale skin and red hair (though by a different genetic route than Homo sapiens), as part of a range of pigmentation.3C. Lalueza-Fox et al., A melanocortin 1 receptor allele suggests varying pigmentation among Neanderthals,Science (October 25, 2007); C. C. S. Cerqueira et al., Predicting homo pigmentation phenotype through genomic data: From neanderthal to James Watson, American Journal of Human Biology, published online 12 March 2012 ahead of print. Neanderthals spent millennia under the often cloudy skies of Europe. But why the red hair? Pigmentation is a puzzle, and we may not have all the pieces yet. There are at least 11 genes involved. So far it looks as though one biological path to paler skin does not interfere with the ancestral dark hair and eyes, while another throws up red hair as a side effect, with another you get blond hair, and mixtures give in between shades. 4F. Liu et al., Digital quantification of human eye color highlights genetic association of three new loci, PLoS Genetics, vol. 6, no. 5 (2010), e1000934; J. Mengel-From et al., Genetic determinants of hair and eye colour in the Scottish and Danish populations, BMC Genetics vol. 10 (December 2009) 88; R.A. Sturm, Molecular genetics of human pigmentation diversity, Human Molecular Genetics, vol. 15, no. 18(R1) (April 2009), R9-17; W. Branicki, Interactions between HERC2, OCA2 and MC1R may influence human pigmentation phenotype, Annals Human Genetics, vol. 73, no. 2 (Mar 2009), pp.160-70. By giving a statistical weighting to 13 single or compound genetic markers from those 11 genes, it is possible to predict hair colour with a high degree of accuracy.5W.Branicki et al., Model-based prediction of human hair color using DNA variants, Human Genetics, online 3 January 2011 before print. There is a completely separate gene for blonde hair which crops up among some Melanesians.6E.E. Kenny et al., Melanesian blond hair is caused by an amino acid change in TYRP1, Science, vol. 336, no. 608 (4 May 2012), p. 554.

Pastoralist women c. 3000 BC shown in a rock painting at TassiliThe rainbow look of Europeans suggests strong selection for a cold climate. It may seem a logical deduction that the process began as man left Africa. Certainly polymorphisms in two genes, ASIP and OCA2 (A355G), seem to play a role in light and dark pigmentation across the globe. They are probably so old that they pre-date the exodus from Africa.7H.L. Norton, Genetic evidence for the convergent evolution of light skin in Europeans and East Asians, Molecular Biology and Evolution, vol. 24 (2007), pp. 710-722. Yet scientists calculate that a new allele causing paler skin cropped up on gene SLC24A5 around 10,000 years ago, probably in the Middle East. It is nicknamed the golden gene, as it also causes golden stripes in zebrafish.8R.L. Lamason et al, SLC24A5 affects pigmentation in zebrafish and man, Science vol. 310 (2005), pp.1782-1786; A. Gibbons, European skin turned pale only recently, gene suggests, Science, vol. 316, no. 5823 (20 April 2007), p.364; V.A. Canfield et al., Molecular phylogeography of a human autosomal skin color locus under natural selection, G3: Genes, Genomes, Genetics, vol. 3, no. 11, pp. 2059-2067 (November 1, 2013).

Artist's impression of a hunter-gatherer from La Brana, Iberia. Support for this theory comes from two hunter-gatherers, one who lived in Iberia and the other in Central Europe around 6000 BC. Both carried the ancestral form of SLC24A5, rather than the mutation which is almost universal in those of European ancestry today, and which is found in an early farmer in Central Europe who lived around 5000 BC. 9I. Lazaridis et al., Ancient human genomes suggest three ancestral populations for Europeans, pre-print online 23 December 2013, Supplementary Information 7; I. Olalde et al., Derived immune and ancestral pigmentation alleles in a 7,000-year-old Mesolithic European, Nature, Published online 26 January 2014.

While the golden gene and three others (SLC45A2, TYRP1 and KITLG) cause most of the paleness of Europeans and their relatives, East Asians have their own colour-drainer (His615Arg in OCA2), as well as KITLG, showing independent evolution after their ancestors moved deep into Asia. The similar distribution of alleles in the KITLG gene within Western Eurasians and East Asians suggests that the mutation causing paler skin occurred before the ancestors of these populations separated. One estimate puts the KITLG change at 30,000 years ago. The Western Eurasian-type alleles at TYRP1, SLC24A5, and SLC45A2 appear to have arisen much later - all within the last 11,000-19,000 years. 10S.Belezal et al., The timing of pigmentation lightening in Europeans, Molecular Biology and Evolution, online ahead of print August 25 2012; M. Edwards et al., Association of the OCA2 polymorphism His615Arg with melanin content in East Asian populations: further evidence of convergent evolution of skin pigmentation, PLoS Genetics, vol. 6, no.3 (March 2010); H.L. Norton, Genetic evidence for the convergent evolution of light skin in Europeans and East Asians, Molecular Biology and Evolution, vol. 24 (2007), pp.710-722.

So it seems that the evolution of colour variation took a leap in the era of the earliest farmers, probably because their diet was lower in vitamin D. Early Europeans boosted their vitamin D intake by eating fatty fish. Salmon bones, fish hooks, and paintings of salmon, trout, and pike have been found in caves they occupied.11G.E. Adán et al., Fish as diet resource in North Spain during the Upper Paleolithic, Journal of Archaeological Science, vol. 36, no. 3 (March 2009), pp. 895-899. The start of farming in the Near East created a higher reliance on cereals. The range of the most recent mutations for lighter colouring suggests that they were first spread by the early farmers. They are found everywhere that farmers migrated from the Near East: Europe, Western Asia and North Africa. For example SLC24A5 is found in 60-70% of the population in Tunisia and Morocco.12G. Lucotte et al., A Decreasing Gradient of 374F Allele Frequencies in the Skin Pigmentation Gene SLC45A2, from the North of West Europe to North Africa, Biochemical Genetics, vol. 48, nos. 1-2 (2010), pp. 26-33. The present range of hair colouring appears to be shown in the rock painting (above) of around 3000 BC from the Tassili n’Ajjer plateau, Algeria.13S. di Lernia and M. Gallinaro, The date and context of Neolithic rock art in the Sahara: engravings and ceremonial monuments from Messak Settafet (south-west Libya), Antiquity, vol. 84, no. 326 (December 2010), pp. 954–975.

Sumerian male worshipper. Standing figure c.2700 BC placed in the Square Temple at Tell Asmar (Metropolitan Museum of Art). Click for a larger image from the museum.Sumerian female worshipper. Standing figure c. 2550 BC in the Nippur temple of Inanna (Metropolitan Museum of Art). Click for a larger image from the museum.Worshippers at Sumerian temples could be depicted with either blue or brown eyes. The same is true of ancient Egyptians of the same period. There is no reason to think that blue eyes predominated in these populations, but every reason to accept that they existed. The predominant gene for blue eyes (rs12913832 GG) is the same in Europe and the Near East. Professor Hans Eiberg and his team analysed the DNA of people with blue eyes in Denmark, Turkey and Jordan. All of them had exactly the same DNA sequence covering half the HERC2 gene. That suggests a common ancestor. Since Eiberg and his colleagues estimated that this mutation arose within the last 6,000 to 10,000 years, they surmised that it spread with the Neolithic.14H. Eiberg et al, Blue eye color in humans may be caused by a perfectly associated founder mutation in a regulatory element located within the HERC2 gene inhibiting OCA2 expression, Human Genetics, vol.123, no 2 (Mar 2008), pp. 177-87.

However now that we have full genomes from two European hunter-gatherers, we find that both carried the rs12913832 GG allele before farmers arrived. Both were probably blue-eyed therefore, though with dark hair and skin.15I. Lazaridis et al., Ancient human genomes suggest three ancestral populations for Europeans, pre-print online 23 December 2013, SI7; I. Olalde et al., Derived immune and ancestral pigmentation alleles in a 7,000-year-old Mesolithic European, Nature, Published online 26 January 2014.

Interestingly there are two other mutations which produce blue eyes and are found world-wide (apart from central/southern Africa), though also concentrated in northern Europe. The rs12913832 GG allele shows strong signals of positive selection in Northern Europe.16M.P. Donnelly et al., A global view of the OCA2-HERC2 region and pigmentation, Human Genetics, online 7 November 2011 ahead of print. What could be the advantage of blue eyes in northern climes? The lower melanin in blue eyes makes it easier to absorb light in winter and so protect against Seasonal Affective Disorder (SAD).17S. Higuchi et al., Influence of eye colors of Caucasians and Asians on suppression of melatonin secretion by light, American Journal of Physiology - Regulatory, Integrative and Comparative Physiology, vol. 292, no. 6 (June 2007), pp. R2352-R2356. Whatever the reason, it seems from testing archaeological samples that selection for variants associated with depigmented hair, skin, and eyes has continued over the last 5,000 years.18S. Wilde et al., Direct evidence for positive selection of skin, hair, and eye pigmentation in Europeans during the last 5,000 y, PNAS, published ahead of print March 10, 2014.

Red hair

Distribution of MC1R red hair alleles There are two types of melanin. Black and brown pigments are formed from eumelanin. Red and yellow result from pheomelanin. Mutations on the MC1R gene, causing loss of only eumelanin, result in yellow or red coat colours in many mammals. Man is no different. Some of these mutations appear in redheads.19Helgi B. Schiöth et al., Loss of function mutations of the human melanocortin 1 receptor are common and are associated with red hair, Biochemical and Biophysical Research Communications, vol. 260, no. 2, (5 July 1999), pp. 488-491. To complicate matters the various red hair alleles on the MC1R gene can have different effects. Some are classed as highly penetrant. Most red-haired individuals (84%) have two highly penetrant alleles (one from each parent), but various other combinations can also result in shades of red.20Niamh Flanagan et al., Pleiotropic effects of the melanocortin 1 receptor (MC1R) gene on human pigmentation, Human Molecular Genetics, vol. 9, no. 17 (2000), pp. 2531-2537; Jonas Mengel-From et al., Genetic determinants of hair and eye colours in the Scottish and Danish populations, BMC Genetics, vol. 10 (2009), 88. Red hair is comparatively rare everywhere today. Partly that is because a person needs to inherit an allele for it from both parents in order to have red hair. A dark-haired person could be quite unaware that he or she is carrying a red hair allele, if he or she has a functioning gene producing eumelanin from the other parent. Having a red-headed child could come as a surprise.

Since there are so many different alleles for red hair, it is highly unlikely that they all cropped up within just one population. Red hair is often considered a Celtic characteristic. Think of Queen Boudica's striking mane of red hair.21Cassius Dio, Roman History, 62.1-12. Certainly Tacitus reported red- heads in Caledonia, long before the inrush of Anglo-Saxons and Vikings. Yet he also saw red hair as a characteristic of the Germani.22Tacitus, Agricola, 11. A recent study proves him right. Yorkshire, Denmark and South-East Wales seem to be harbouring more such alleles than Ireland.23E. Røyrvik, Western Celts? A genetic impression of Britain in Atlantic Europe, in B. Cunliffe and J.T. Koch (eds.), Celtic from the West (2010) pp. 83-106.

So red hair is not restricted to Celts. It is not even restricted to Indo-Europeans. In the 4th century BC Herodotus described a nomadic, foraging tribe called the Budini with piercing grey eyes and bright red hair, who lived in the forest east of the River Don and 15 days journey north of the Sea of Azov.24Herodotus, The Histories, 4.21-2, 108-9. They sound like the Udmurts, who claim as many red-heads as the Irish. The Udmurt Republic lies in Russia, in the forest zone between two tributaries of the Volga. The Udmurts speak a Finno-Ugric language. They now celebrate their rufosity each September with the Red Festival. The Dutch followed suit with Red Head Day. So far there has been no world-wide scientific sampling to settle the vexed question of which nation really has the highest percentage of red-heads.

9th-century AD fresco from the Bezeklik grottoes near Turfan, Tarim Basin, China.Equally tricky is the mummy debate. Some mummies from Egypt and the Tarim Basin have red hair. Is this just the result of fading after death? Or was henna used? Or are some of these mummies the genuine copper-haired article? The answer could be a combination of all three. The earliest mummies are the result of natural preservation in desert sands. The British Museum houses a chap once affectionately nicknamed Ginger, buried about 3400 BC in predynastic Egypt. Could the red locks that gave him his nickname be faded from brown? The mummies now emerging from another predynastic cemetery may provide answers. At Hierakonpolis 43 (c.3600-3400BC), most of the hair found on mummies is very dark brown, showing that this colour can be preserved for millennia, and that it was the most common. Yet male burial no. 79 had natural wavy, red hair.25J. Fletcher, The Secrets of the Locks Unraveled. Nekhen News, Vol 10, (Milwaukee Public Museum 1998), pp. 7-8. Ramsess II (d.1213 BC) used henna to cover his grey hair in old age, but fragments of pigmentation in the roots indicated that it was originally a natural red. If red hair ran in his family, that might explain the occurence of the name Seti among them, red being associated with the dangerous god Set. 26L. Balout and C. Roubet (eds.), La Momie de Ramsès II: Contribution Scientifique a l'Egyptologie 1976-1977, (Paris: Éditions Recherche sur les Civilisations/Muséum National d'Histoire Naturelle/Musée de l'Homme 1985).

Red hair was evidently rare in Ancient Egypt, as it is in North Africa today. But it crops up occasionally among the Berbers of Algeria and Morocco, who seem to be descended from the first farmers to arrive in North Africa, depicted with a range of hair colour in the rock painting at Tassili. There is no reason to imagine that the pharaohs of the 19th dynasty were foreign to Egypt.

The issue of fading pigments does arise with ancient depictions too. The rock painting of the Tassili ladies above is convincing, as it shows a variety of hair colours. The brown has not faded too much. Rock paintings are hard to date precisely, but this may be the earliest image of a red-head. Similarly this painting of Buddhist monks from the Tarim Basin makes a clear distinction between the red-brown hair and beard of the presumably Indo-European (Tocharian) man on the left and the grey or faded black hair of the monk on the right.

Height

Average male European height by countries from Grasgruber 2014It has long been observed that tall people tend to have tall children, but is the explanation genes or lifestyle? Scientists have managed to disentangle the two by twin studies. Identical twins reared in different households tend to be similar in height, but not absolutely identical. About 80 percent of the difference in height between individuals within a population is determined by genetic factors, and scientists are close to pinning down exactly which genes are involved. The rest of the variation can be explained mainly by nutrition. 27M. B. Lanktree et al., Meta-analysis of dense genecentric association studies reveals common and uncommon variants associated with height, The American Journal of Human Genetics, (online 30 December 2010 ahead of print); H.L. Allen et al., Hundreds of variants clustered in genomic loci and biological pathways affect human height, Nature, (advance online publication 29 September 2010); J. Yang et al., Common SNPs explain a large proportion of the heritability for human height, Nature Genetics, (published online ahead of print 20 June 2010); Å. Johansson et al., Common variants in the JAZF1 gene associated with height identified by linkage and genome-wide association analysis, Human Molecular Genetics, vol. 18, no. 2 (2009), pp. 373–380; P.M. Visscher, Sizing up human height variation, Nature Genetics, vol. 40 (2008), pp. 489-490. Yet these figures apply to twins brought up in the same era and generally within the same country, so their diet is unlikely to be dramatically different. What happened when people shifted from hunting to farming? It meant a huge change in diet from one heavy on meat to one heavy on cereals. Archaeologists in Europe can see the result in the human skeletons they find. The early farmers were shorter and slighter than their hunting forebears. Contributory factors may have been higher fertility and early weaning among the settled farmers. Later dairy farming created a cheap and regular source of protein in milk, raising average heights among pastoralists.28J. Piontek, B. Jerszyńska, S. Segeda, Long bones growth variation among prehistoric agricultural and pastoral populations from Ukraine (Bronze era to Iron age), Variability and Evolution, vol. 9, (2001), pp. 61-73; A. Mummert et al., Stature and robusticity during the agricultural transition: Evidence from the bioarchaeological record, Economics and Human Biology, vol. 9, no. 3 (July 2011), pp. 284-301.

Average heights (combining male and female) rose and fell in Europe over the centuries as we move from prehistory into early history. Surprisingly the average height of Mediterraneans from this sample was lowest during the period of the Roman Empire, suggesting that not all its citizens benefitted from the high living standards of the Roman elite. In general northern Europeans maintained a height advantage over Mediterraneans. That pattern is still apparent today, with the exception of Greece and the Balkans. The tallest men are found in Northern/Central Europe and the former Yugoslavia. The shortest European population on average is that of Sardinia. Some natural selection there in favour of shorter stature has been suggested. 29Nikola Köpke, Regional Differences and Temporal Development of the Nutritional Status in Europe from the 8th century B.C. until the 18th century A.D., Dissertation 2008 University Tübingen; Grasgruber et al., The role of nutrition and genetics as key determinants of the positive height trend, Economics and Human Biology, vol. 15 (December 2014), pp. 81–100; M. Zoledziewska et al., Height-reducing variants and selection for short stature in Sardinia, Nature Genetics, vol. 47, pp. 1352–1356 (September 2015).

Head shapeHead-shaping among the Mangbetu of the CongoAnother way in which humans vary is the shape of the skull. Normally we only have to think about this if we are selecting a helmet, or a custom-made hat. Crania can be dolichocephalic (long from back to front), mesocephalic (moderate) or brachycephalic (broad). Skull variation caught the attention of pioneers in anthropology. By the pre-war period elaborate classifications of skull types were in use, but gradually unease developed about seeing these as inherited. Could infant head-binding, diet or other environmental factors be more important in determining head-shape? Head-binding has appeared in a number of cultures. The Mangbetu people of the Congo were still elongating the skulls of their infants to the 1950s, so the technique could be observed. The same type of head-shaping was common in the Near East in the 6th and 5th millennia BC. It produced skulls so long that they appear alien.30K.O. Lorentz, Ubaid headshaping, in R.A. Carter and G. Philip, Beyond the Ubaid (2010), pp. 125-148.

However in present populations recent studies suggest that the heritability of craniofacial traits is actually quite high.31A. Jelenkovic, Contribution of genetics and environment to craniofacial anthropometric phenotypes in Belgian nuclear families, Human Biology vol. 80, no.6 (2008), pp.637-654; N. Martínez-Abadías et al, Heritability of human cranial dimensions: comparing the evolvability of different cranial regions,Journal of Anatomy, vol. 214, no. 1, (January 2009), pp. 19-35. So how did these variations arise? There is enough of a correlation between an extremely cold climate and brachycephaly to suggest that natural selection favoured this type of skull in cold conditions, as it minimised heat loss, thanks to the reduced surface/mass ratio. However the distribution of brachycephaly today can mainly be explained by genetic drift. 32L. Betti et al, The relative role of drift and selection in shaping the human skull, The American Journal of Physical Anthropology (2009). So it may be of use in tracing migration. But since these are traits inherited autosomally, they could change over the generations as people mix. This is another Gordian knot that genetics has the potential to slice through. Ancient DNA can tell us with certainty who is descended from whom.

Is there such a thing as a typical Germanic foot-shape? I have my doubts, but retired podiatrist Phyllis Jackson noticed a difference between the typical foot-shape of the English (broad, with the toes sloping down sharply) and that prevailing in Cornwall, Ireland, Scotland and Wales (narrow with a more level toe line). She went on to investigate skeletal material and found a considerable difference between the feet of the Roman-British and those buried with Anglo-Saxon grave goods. Her article Footloose in Archaeology in Current Archaeology (1995) created quite a stir. She went on to create a scholarly version for publication elsewhere.33P. Jackson, Footloose in Archaeology, Journal of British Podiatric Medicine, vol. 51, no. 5 (1996), pp. 67-70.

Notes

If you are using a browser with up-to-date support for W3C standards e.g. Firefox, Google Chrome, IE 8 or Opera, hover over the superscript numbers to see footnotes online. If you are using another browser, select the note, then right-click, then on the menu click View Selection Source. If you print the article out, or look at print preview online, the footnotes will appear here.

  1. M. Jobling, M. E. Hules and C. Tyler-Smith, Human Evolutionary Genetics (2004), chapter 2.
  2. M. Jobling, M. E. Hules and C. Tyler-Smith, Human Evolutionary Genetics (2004), section 13.3 and box 13.4 provide an introduction to the subject, updated by A. Juzeniene et al., Development of different human skincolors: A review highlighting photobiological and photobiophysical aspects, Journal of Photochemistry and Photobiology B: Biology, vol. 96, no. 2 (3 August 2009), pp. 93-100; M. Rode von Essen et al, Vitamin D controls T cell antigen receptor signaling and activation of human T cells, Nature Immunology (online ahead of print 7 March 2010).
  3. C. Lalueza-Fox et al., A melanocortin 1 receptor allele suggests varying pigmentation among Neanderthals, Science, (October 25, 2007); C. C. S.Cerqueira et al., Predicting homo pigmentation phenotype through genomic data:From neanderthal to James Watson, American Journal of Human Biology published online 12 March 2012 ahead of print.
  4. F. Liu et al., Digital Quantification of Human Eye Color Highlights Genetic Association of Three New Loci, PLoS Genetics, vol. 6, no. 5 (2010), e1000934; J. Mengel-From et al., Genetic determinants of hair and eye colour in the Scottish and Danish populations, BMC Genetics vol. 10 (December 2009) 88; R.A. Sturm, Molecular genetics of human pigmentation diversity, HumanMolecular Genetics, vol. 15, no. 18(R1) (April 2009), R9-17; W. Branicki, Interactions between HERC2, OCA2 and MC1R may influence human pigmentation phenotype, Annals Human Genetics, vol. 73, no. 2 (Mar 2009), pp.160-70.
  5. W. Branicki et al., Model-based prediction of human hair color using DNA variants, Human Genetics, online 3 January 2011 before print.
  6. E. E. Kenny et al., Melanesian blond hair is caused by an amino acid change in TYRP1, Science, vol. 336, no. 608 (4 May 2012), p. 554.
  7. H.L. Norton, Genetic evidence for the convergent evolution of light skin in Europeans and East Asians, Molecular Biology and Evolution, vol. 24 (2007), pp.710-722.
  8. R. L. Lamason et al, SLC24A5 affects pigmentation in zebrafish and man, Science, vol. 310 (2005), pp.1782-1786; A. Gibbons, European skin turned pale only recently, gene suggests, Science, vol. 316, no. 5823 (20 April 2007), p.364; V.A. Canfield et al., Molecular phylogeography of a human autosomal skin color locus under natural selection, G3: Genes, Genomes, Genetics, vol. 3, no. 11, pp. 2059-2067 (November 1, 2013).
  9. I. Lazaridis et al., Ancient human genomes suggest three ancestral populations for Europeans, pre-print online 23 December 2013, SI7; I. Olalde et al., Derived immune and ancestral pigmentation alleles in a 7,000-year-old Mesolithic European, Nature, Published online 26 January 2014.
  10. S. Belezal et al., The timing of pigmentation lightening in Europeans, Molecular Biology and Evolution, online ahead of print August 25 2012; M. Edwards et al., Association of the OCA2 polymorphism His615Arg with melanin content in East Asian populations: further evidence of convergent evolution of skin pigmentation, PLoS Genetics, vol. 6, no.3 (March 2010); H.L. Norton, Genetic evidence for the convergent evolution of light skin in Europeans and East Asians, Molecular Biology and Evolution, vol. 24 (2007), pp. 710-722.
  11. G. E. Adán et al., Fish as diet resource in North Spain during the Upper Paleolithic, Journal of Archaeological Science, vol. 36, no. 3 (March 2009), pp. 895-899.
  12. G. Lucotte et al., A Decreasing Gradient of 374F Allele Frequencies in the Skin Pigmentation Gene SLC45A2, from the North of West Europe to North Africa, Biochemical Genetics, vol. 48, nos. 1-2 (2010), pp. 26-33.
  13. S. di Lernia and M. Gallinaro, The date and context of Neolithic rock art in the Sahara: engravings and ceremonial monuments from Messak Settafet (south-west Libya), Antiquity, vol. 84, no. 326 (December 2010), pp. 954–975.
  14. H. Eiberg et al, Blue eye color in humans may be caused by a perfectly associated founder mutation in a regulatory element located within the HERC2 gene inhibiting OCA2 expression, Human Genetics, vol. 123, no 2 (Mar 2008), pp. 177-87.
  15. I. Lazaridis et al., Ancient human genomes suggest three ancestral populations for Europeans, pre-print online 23 December 2013, SI7; I.Olalde et al., Derived immune and ancestral pigmentation alleles in a7,000-year-old Mesolithic European, Nature, Published online 26January 2014.
  16. M. P. Donnelly et al., A global view of the OCA2-HERC2 region and pigmentation, Human Genetics, online 7 November 2011 ahead of print.
  17. S. Higuchi et al., Influence of eye colors of Caucasians and Asians on suppression of melatonin secretion by light, American Journal of Physiology - Regulatory, Integrative and Comparative Physiology, vol. 292, no. 6 (June 2007), pp. R2352-R2356.
  18. S. Wilde et al., Direct evidence for positive selection of skin, hair, and eye pigmentation in Europeans during the last 5,000 y, PNAS, published ahead of print March 10, 2014.
  19. Helgi B. Schiöth et al., Loss of function mutations of the human melanocortin 1 receptor are common and are associated with red hair, Biochemical and Biophysical Research Communications, vol. 260, no. 2, (5 July 1999), pp. 488-491.
  20. Niamh Flanagan et al., Pleiotropic effects of the melanocortin 1 receptor (MC1R) gene on human pigmentation, Human Molecular Genetics, vol. 9, no. 17 (2000), pp. 2531-2537; Jonas Mengel-From et al., Genetic determinants of hair and eye colours in the Scottish and Danish populations, BMC Genetics, vol. 10 (2009), 88.
  21. Cassius Dio, Roman History, 62.1-12.
  22. Tacitus, Agricola, 11.
  23. E. Røyrvik, Western Celts? A genetic impression of Britain in Atlantic Europe, in B. Cunliffe and J.T. Koch (eds.), Celtic from the West (2010) pp. 83-106.
  24. Herodotus, The Histories, 4.21-2, 108-9.
  25. Joann Fletcher, The Secrets of the Locks Unraveled. Nekhen News, Vol 10, (Milwaukee Public Museum 1998), pp. 7-8.
  26. L. Balout and C. Roubet (eds.), La Momie de Ramsès II: Contribution Scientifique a l'Egyptologie 1976-1977, (Paris: Éditions Recherche sur les Civilisations/Muséum National d'Histoire Naturelle/Musée de l'Homme 1985).
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