2.5.1.4 Genetic

 0 Contents 2 Background 2.5 Societal 2.5.1 Europe

Farmers 2.5.1.6

2.5.1.5 Who do you look like?

Introduction

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? 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. 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 University of California: Berkeley provides a quick, animated guide toSex 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 eye colour
Distribution of light hair

Colouring 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 for that very reason makes 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.

Interestingly it seems that the Neanderthals were ahead of us in developing pale skin and red hair (though by a different genetic route than Homo sapiens).3C. Lalueza-Fox et al., A melanocortin 1receptor allelesuggests varying pigmentation among Neanderthals,Science,(October 25, 2007).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.

Pastoralist women c. 3000 BC shown in a rock painting at Tassili

The 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. Yet scientists calculate that the predominant gene for blue eyes appeared much more recently: between 6,000 and 10,000 years ago. 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 that all the blue-eyed people in the world today have a common ancestor. He or she just happened to have a mutation that corrupted the code.6H. 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. At around the same time a new allele causing paler skin cropped up on gene SLC24A5, nicknamed the golden gene, as it also causes golden stripes in zebrafish.7R.L. Lamason et al, SLC24A5 affects pigmentation in zebrafish and man, Science vol. 310 (2005), pp.1782-1786. While the golden gene and two others (SLC45A2 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. However the similar distribution of alleles in the KITLG gene within Western Eurasians and East Asians suggests that some selection for paler skin is older.8M. 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.

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.
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.

So the evolution of colour variation may have begun in Africa, but 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.9G.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.10G. 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.11S. 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. 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 and light hair predominated in these populations, but every reason to suppose that they existed. So the surviving mutations probably happened somewhere in the Near East, and gave their carriers enough of an advantage to multiply. Natural selection, favouring the lighter colours most strongly in more northerly latitudes, would create the distribution we see today. For fun, you might like the interactive What colour eyes would your children have?, devised by the Tech Museum.

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.12Helgi 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 hairalleles 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.13Niamh 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. Professor Jonathan Rees, Professor of Dermatology at the University of Edinburgh gives a fuller account online for the layman: non-expert guide to the genetics of red hair (and freckles).

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.14Cassius 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.15Tacitus, Agricola, 11. A recent study proves him right. Yorkshire, Denmark and South-East Wales seem to be harbouring more such alleles than Ireland.16E. 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-Euopeans. 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.17Herodotus, 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 theRed 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. AtHierakonpolis 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.18J. 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 occurance of the name Seti among them, red being associated with the dangerous god Set. 19L. 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

Height by century in centimetres

It 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.20M. 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.21J. 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. In North America, European colonists encountered nomadic buffalo-hunters on the Great Plains. Systematic measurements by Franz Boas in 1892 showed that these Native Americans were the tallest people in the world at that time for whom we have reliable statistics. With an average height of 172.2 cm, they were 3 to 11 cm taller than contemporary Europeans, and slightly taller than European-Australians. His work came just in time. The buffalo herds were in decline and a way of life was almost over.22R.H. Steckel and J.M. Prince, Tallest in the World: Native Americans of the Great Plains in the Nineteenth Century, American Economic Review, vol. 91, no.1 (March 2001), pp. 287-294.

Head-shaping among the Mangbetu of the Congo
Head shape

Another 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.23K.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.24A. 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. 25L. 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.

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).
  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. 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.
  7. R.L. Lamason et al, SLC24A5 affects pigmentation in zebrafish and man, Science, vol. 310 (2005), pp.1782-1786.
  8. 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.
  9. 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.
  10. 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.
  11. 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.
  12. 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.
  13. 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.
  14. Cassius Dio, Roman History, 62.1-12.
  15. Tacitus, Agricola, 11.
  16. 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.
  17. Herodotus, The Histories, 4.21-2, 108-9.
  18. Joann Fletcher, The Secrets of the Locks Unraveled. Nekhen News, Vol 10, (Milwaukee Public Museum 1998), pp. 7-8.
  19. 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).
  20. M. 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.
  21. J. 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.
  22. R.H. Steckel and J.M. Prince, Tallest in the World: Native Americans of the Great Plains in the Nineteenth Century, American Economic Review, vol. 91, no.1 (March 2001), pp. 287-294.
  23. K.O. Lorentz, Ubaid headshaping, in R.A. Carter and G. Philip, Beyond the Ubaid (2010), pp. 125-148.
  24. A. 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.
  25. L. Betti et al, The relative role of drift and selection in shaping the human skull, The American Journal of Physical Anthropology (2009).

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