Bronze Age people from Ireland had steppe ancestry and R1b

From the paper:

We were able to deduce that Neolithic Ballynahatty had a dark hair shade (99.5% probability), most likely black (86.1% probability), and brown eyes (97.3% probability) (46). Bronze Age Rathlin1 probably had a light hair shade (61.4%) and brown eyes (64.3%). However, each Rathlin genome possessed indication of at least one copy of a haplotype associated with blue eye color in the HERC2/OCA2 region.

and:

Third, we followed the methods described in Haak et al. (9), which use a collection of outgroup populations, to estimate the mixture proportions of three different sources, Linearbandkeramik (Early Neolithic; 35 ± 6%), Loschbour (WHG; 26 ± 12%), and Yamnaya (39 ± 8%), in the total Irish Bronze Age group. These three approaches give an overlapping estimate of ∼32% Yamnaya ancestry.

PNAS doi: 10.1073/pnas.1518445113

Neolithic and Bronze Age migration to Ireland and establishment of the insular Atlantic genome

Lara M. Cassidy, Rui Martiniano et al.

The Neolithic and Bronze Age transitions were profound cultural shifts catalyzed in parts of Europe by migrations, first of early farmers from the Near East and then Bronze Age herders from the Pontic Steppe. However, a decades-long, unresolved controversy is whether population change or cultural adoption occurred at the Atlantic edge, within the British Isles. We address this issue by using the first whole genome data from prehistoric Irish individuals. A Neolithic woman (3343–3020 cal BC) from a megalithic burial (10.3× coverage) possessed a genome of predominantly Near Eastern origin. She had some hunter–gatherer ancestry but belonged to a population of large effective size, suggesting a substantial influx of early farmers to the island. Three Bronze Age individuals from Rathlin Island (2026–1534 cal BC), including one high coverage (10.5×) genome, showed substantial Steppe genetic heritage indicating that the European population upheavals of the third millennium manifested all of the way from southern Siberia to the western ocean. This turnover invites the possibility of accompanying introduction of Indo-European, perhaps early Celtic, language. Irish Bronze Age haplotypic similarity is strongest within modern Irish, Scottish, and Welsh populations, and several important genetic variants that today show maximal or very high frequencies in Ireland appear at this horizon. These include those coding for lactase persistence, blue eye color, Y chromosome R1b haplotypes, and the hemochromatosis C282Y allele; to our knowledge, the first detection of a known Mendelian disease variant in prehistory. These findings together suggest the establishment of central attributes of the Irish genome 4,000 y ago.

Link

Prehistoric farmers from northern Greece had lactose intolerance, brown eyes, dark skin

According to this:

Πολύ σημαντικό πρόσφατο εύρημα αποτελεί η ανάκτηση ολόκληρων γονιδιωμάτων από τρεις προϊστορικούς αγρότες, που έζησαν στη Βόρεια Ελλάδα 7.500 με 5.500 χρόνια πριν από σήμερα. Τα δεδομένα αυτά αναλύονται και αναμένεται να ρίξουν φως στις προγονικές σχέσεις των πρώτων Ευρωπαίων και να δώσουν πλήθος πληροφοριών, που συνδέονται με λειτουργικά και μορφολογικά χαρακτηριστικά. Ήδη, είναι γνωστό, ότι κάποιοι νεολιθικοί πρόγονοί μας δε μπορούσαν να πέψουν το γάλα, ήταν δηλαδή δυσανεκτικοί στη λακτόζη και είχαν καστανά μάτια και σκουρόχρωμη επιδερμίδα.

Related video:

Eye color and alcohol dependence

American Journal of Medical Genetics Part B: Neuropsychiatric Genetics DOI: 10.1002/ajmg.b.32316

Eye color: A potential indicator of alcohol dependence risk in European Americans

Arvis Sulovari et al.

In archival samples of European-ancestry subjects, light-eyed individuals have been found to consume more alcohol than dark-eyed individuals. No published population-based studies have directly tested the association between alcohol dependence (AD) and eye color. We hypothesized that light-eyed individuals have a higher prevalence of AD than dark-eyed individuals. A mixture model was used to select a homogeneous sample of 1,263 European-Americans and control for population stratification. After quality control, we conducted an association study using logistic regression, adjusting for confounders (age, sex, and genetic ancestry). We found evidence of association between AD and blue eye color (P = 0.0005 and odds ratio = 1.83 (1.31–2.57)), supporting light eye color as a risk factor relative to brown eye color. Network-based analyses revealed a statistically significant (P = 0.02) number of genetic interactions between eye color genes and AD-associated genes. We found evidence of linkage disequilibrium between an AD-associated GABA receptor gene cluster, GABRB3/GABRG3, and eye color genes, OCA2/HERC2, as well as between AD-associated GRM5 and pigmentation-associated TYR. Our population-phenotype, network, and linkage disequilibrium analyses support association between blue eye color and AD. Although we controlled for stratification we cannot exclude underlying occult stratification as a contributor to this observation. Although replication is needed, our findings suggest that eye pigmentation information may be useful in research on AD. Further characterization of this association may unravel new AD etiological factors. © 2015 Wiley Periodicals, Inc.

Link

Bronze Age warrior from Poland

Google translation of original article:

Skull warrior was in such good condition that the museum was tempted by an experiment - a reconstruction of his face. Tasks undertaken by the research team of Dr. Dorothy Lorkiewicz-Muszyńska of the Department of Forensic Medicine, University of Medical Sciences. Every day with their ability to use the police, for example, when you need to identify a murder victim. The first step was to make a 3D scan of the skull.

- At the base using a special computer program was applied to the muscle tissue - explains the director Bartecki. - Method shows more than 90 percent. compliance with the real appearance of a man - says.

Proved invaluable assistance skeleton results Rogalin. Also genetic. Thanks to them, we know that the warrior had a dark complexion, dark hair and eyes.

This combination of traits is rather uncommon in modern Poles. It seems that eastern Europeans looked quite different four thousand years ago than they do today.

Dark pigmentation of Eneolithic and Bronze Age kurgan groups from eastern Europe

This is a very exciting new study that seems to parallel some results from early west Europeans. The authors invoke selection as a possible cause for the massive change in frequency between the Bronze Age and present-day Ukrainians.

An invocation of selection as an explanation requires evidence population continuity, otherwise changes in allele frequency may involve migration of a new frequency-differentiated new population; for example, the massive change in pigmentation in North America over the last 500 years is not due to selection but to migration of Europeans. The authors cannot reject population continuity on the basis of mtDNA haplogroup frequencies, although autosomal data may be more informative for that purpose.

In any case, the fact that the limited sample from western Europe and the much more extensive sample from eastern Europe both show a darker pigmentation than modern Europeans does suggest that interesting changes happened in Europe over the last few thousand years and samples from more recent time periods may better determine the pace of this change.

From the paper:

In sum, a combination of selective pressures associated with living in northern latitudes, the adoption of an agriculturalist diet, and assortative mating may sufficiently explain the observed change from a darker phenotype during the Eneolithic/Early Bronze age to a generally lighter one in modern Eastern Europeans, although other selective factors cannot be discounted. The selection coefficients inferred directly from serially sampled data at these pigmentation loci range from 2 to 10% and are among the strongest signals of recent selection in humans.

UPDATE: 

The classical Greeks did of course notice that the inhabitants of the north Pontic hinterland, collectively known as Scythians, were extraordinarily light-pigmented. This would imply that major pigmentation change occurred in the steppe over a time span of Bronze Age-Classical Antiquity rather than Bronze Age-present; this would imply even higher selection coefficients (if selection over a population exhibiting continuity is at play).

The Scythians were also thought to be recent arrivals from the east so it is not clear if they were descended from the Bronze Age population of eastern Europe; the crazy selection coefficients that would need to be assumed if there was indeed population continuity might imply that Herodotus got it right again, and the Scythians did in fact arrive from elsewhere. That would of course also imply that people from Central Asia and Siberia (where the Scythians may have come from) were originally lighter than Europeans which does find support from an older study on southern Siberian remains. Ironically, if that is the case, it would mean that the famous light-pigmented mummies of different parts of Inner Asia may not be long-lost European descendants -- as it has sometimes been presumed on the basis of modern-day clines of pigmentation. As usual, ancient DNA continues to surprise.

PNAS doi: 10.1073/pnas.1316513111

Direct evidence for positive selection of skin, hair, and eye pigmentation in Europeans during the last 5,000 y

Sandra Wilde et al.

Eye, hair, and skin pigmentation are highly variable in humans, particularly in western Eurasian populations. This diversity may be explained by population history, the relaxation of selection pressures, or positive selection. To investigate whether positive natural selection is responsible for depigmentation within Europe, we estimated the strength of selection acting on three genes known to have significant effects on human pigmentation. In a direct approach, these estimates were made using ancient DNA from prehistoric Europeans and computer simulations. This allowed us to determine selection coefficients for a precisely bounded period in the deep past. Our results indicate that strong selection has been operating on pigmentation-related genes within western Eurasia for the past 5,000 y.

Link

Population structure in the Netherlands

The three PCs are color-coded in panels b,c,d.

European Journal of Human Genetics , (27 March 2013) | doi:10.1038/ejhg.2013.48

Population structure, migration, and diversifying selection in the Netherlands

Abdel Abdellaoui et al.

Genetic variation in a population can be summarized through principal component analysis (PCA) on genome-wide data. PCs derived from such analyses are valuable for genetic association studies, where they can correct for population stratification. We investigated how to capture the genetic population structure in a well-characterized sample from the Netherlands and in a worldwide data set and examined whether (1) removing long-range linkage disequilibrium (LD) regions and LD-based SNP pruning significantly improves correlations between PCs and geography and (2) whether genetic differentiation may have been influenced by migration and/or selection. In the Netherlands, three PCs showed significant correlations with geography, distinguishing between: (1) North and South; (2) East and West; and (3) the middle-band and the rest of the country. The third PC only emerged with minimized LD, which also significantly increased correlations with geography for the other two PCs. In addition to geography, the Dutch North–South PC showed correlations with genome-wide homozygosity (r=0.245), which may reflect a serial-founder effect due to northwards migration, and also with height (♂: r=0.142, ♀: r=0.153). The divergence between subpopulations identified by PCs is partly driven by selection pressures. The first three PCs showed significant signals for diversifying selection (545 SNPs - the majority within 184 genes). The strongest signal was observed between North and South for the functional SNP in HERC2 that determines human blue/brown eye color. Thus, this study demonstrates how to increase ancestry signals in a relatively homogeneous population and how those signals can reveal evolutionary history.

Link

Admixture and pigmentation in Cape Verde

The interesting thing about this paper is that it shows that one can explain skin color in people from Cape Verde better if one uses their proportion of African/European admixture, rather than by looking at individuals' genotypes at loci associated with the trait. This probably means that many loci of minor effect on the trait differentiate Europeans from Africans.

Prediction of skin color based on ancestry is much better than prediction of eye color from the same, which is not surprising since skin color is a highly polygenic trait.

PLoS Genet 9(3): e1003372. doi:10.1371/journal.pgen.1003372

Genetic Architecture of Skin and Eye Color in an African-European Admixed Population

Sandra Beleza et al.

Abstract

Variation in human skin and eye color is substantial and especially apparent in admixed populations, yet the underlying genetic architecture is poorly understood because most genome-wide studies are based on individuals of European ancestry. We study pigmentary variation in 699 individuals from Cape Verde, where extensive West African/European admixture has given rise to a broad range in trait values and genomic ancestry proportions. We develop and apply a new approach for measuring eye color, and identify two major loci (HERC2[OCA2] P = 2.3×10−62, SLC24A5 P = 9.6×10−9) that account for both blue versus brown eye color and varying intensities of brown eye color. We identify four major loci (SLC24A5 P = 5.4×10−27, TYR P = 1.1×10−9, APBA2[OCA2] P = 1.5×10−8, SLC45A2 P = 6×10−9) for skin color that together account for 35% of the total variance, but the genetic component with the largest effect (~44%) is average genomic ancestry. Our results suggest that adjacent cis-acting regulatory loci for OCA2 explain the relationship between skin and eye color, and point to an underlying genetic architecture in which several genes of moderate effect act together with many genes of small effect to explain ~70% of the estimated heritability.

Link

Multiplex determination of eye and hair color

From the paper:

Sample S24 represents a controversial case from the Benedictine Abbey in  Tyniec near Krakow. During the work undertaken in the crypt of the St. Peter and Paul  church belonging to the Abbey, 17 skeletons of alleged abbots were found. The burial was  dated to the period of the 12th to 14th centuries. Unexpectedly, the anthropological  examination revealed that two skeletons may be of female origin, which indeed was  confirmed by DNA analysis (data not shown), while only male monks were expected. One of the two DNA samples was sufficiently preserved to enable analysis of other nuclear markers  (data not shown) and was used here for HIrisPlex analysis. The mysterious woman was  predicted to have dark blond/brown hair (accuracy of 78.5%) and brown eyes (accuracy of 90.4%), (Table 2 and Figure 2B). 

... 

Two medieval  skeletons were found under the floor between the chancel and the nave of the church. Based  on historical markers the grave was dated to originate from the 14th century. Further  anthropological examinations indicated that the S25 male died at the approximate age of 60,  whereas the S26 male was approximately 75 years old at the time of death. It is alleged that  the skeletons belong to members of the Teczynski family, representing noble Polish magnates  of medieval times. The tooth collected from the deeper burial (S25) was found to be seriously  affected by decay, which was reflected by a very low DNA concentration (3 pg/µl) and  incomplete autosomal and Y chromosome STR profiles (NGM and Yfiler). Complete  mtDNA HVI and HVII profiles were generated in both teeth (data not shown). From these  data it was possible to conclude that both skeletons are of male origin and are unrelated in  both maternal and paternal lines. From the partial HIrisPlex profile ascertained from S25 we  successfully inferred blue eye colour (P = 0.899, accuracy of 95.6%), but hair colour could  not be inferred because of missing genotypes at three DNA variants (N29insA, rs1805005,  rs2228479). The sample S26 revealed a prediction of blond hair colour (P = 0.784) together  with a light hair colour shade (P = 0.918) concluding that the individual had light blond hair  (accuracy of 69.5%). Eye colour prediction of S26 revealed blue eyes (P = 0.919, accuracy of  97.4%) (Table 2).

Wikipedia article on Tęczyński family.

Investigative Genetics 2013, 4:3 doi:10.1186/2041-2223-4-3

Bona fide colour: DNA prediction of human eye and hair colour from ancient and contemporary skeletal remains

Jolanta Draus-Barini

Abstract (provisional)

Background

DNA analysis of ancient skeletal remains is invaluable in evolutionary biology for exploring the history of species, including humans. Contemporary human bones and teeth, however, are relevant in forensic DNA analyses that deal with the identification of perpetrators, missing persons, disaster victims or family relationships. They may also provide useful information towards unravelling controversies that surround famous historical individuals. Retrieving information about a deceased person's externally visible characteristics can be informative in both types of DNA analyses. Recently, we demonstrated that human eye and hair colour can be reliably predicted from DNA using the HIrisPlex system. Here we test the feasibility of the novel HIrisPlex system at establishing eye and hair colour of deceased individuals from skeletal remains of various post-mortem time ranges and storage conditions.

Methods

Twenty-one teeth between 1 and approximately 800 years of age and 5 contemporary bones were subjected to DNA extraction using standard organic protocol followed by analysis using the HIrisPlex system.

Results

Twenty-three out of 26 bone DNA extracts yielded the full 24 SNP HIrisPlex profile, therefore successfully allowing model-based eye and hair colour prediction. HIrisPlex analysis of a tooth from the Polish general W[latin small letter l with stroke]adys[latin small letter l with stroke]aw Sikorski (1881 to 1943) revealed blue eye colour and blond hair colour, which was positively verified from reliable documentation. The partial profiles collected in the remaining three cases (two contemporary samples and a 14th century sample) were sufficient for eye colour prediction.

Conclusions

Overall, we demonstrate that the HIrisPlex system is suitable, sufficiently sensitive and robust to successfully predict eye and hair colour from ancient and contemporary skeletal remains. Our findings, therefore, highlight the HIrisPlex system as a promising tool in future routine forensic casework involving skeletal remains, including ancient DNA studies, for the prediction of eye and hair colour of deceased individuals.

Link

Blue eyes, facial shape, and perceived trustworthiness

A new paper suggests that Czechs tend to view brown-eyed people as more trustworthy than blue-eyed ones, although the difference seems to be due to differences in facial structure between brown- and blue-eyed people; an article in Scientific American covers this new paper fairly well.

I will add that the location of the sample (Czech Republic) is interesting, as it is intermediate between the Baltic area (where light eye pigmentation reaches quasi-fixation, and, hence, presumably, light eyes are not viewed with any suspicion) and southeastern Europe and Anatolia (where there is well-documented folklore about the association of eye pigmentation with the "evil eye").

I had encountered an explanation for this phenomenon in a work by P.G. Maxwell-Stuart on ancient color terminology, in which an argument was made that in predominantly dark-eyed peoples, light eyes -because of their rarity- may have an indirect association with glaucoma and viewed suspiciously for that reason -perceived chance of morbidity; the Wikipedia article suggests the phenomenon is explained on the basis of encounters with light-eyed foreigners who might be unaware of cultural norms against direct staring. But, the frequency of different eye colors in Czechs today is probably fairly balanced, making either explanation unsatisfactory.

Getting back to the article at hand, it appears that -at least in men- blue eyes are associated with a suite of other facial features. Razib offers the suggestion that the possible disadvantage conferred by reduced "trustworthiness" may be compensated in another way through pleiotropy, and the authors suggest:

The trade-off between a preference for colorful and visible physical features and the advantage of a trustworthy-looking face might have contributed to the high variability of European eye and hair color.

But, I'll get back to the possibility that the phenomenon may be driven by a historical process, i.e., the encounter between peoples who differed statistically in eye pigmentation and other facial features.

The picture on the left is from the Gospel Book of Otto III and is about 1,000 years old. Now, all eyes appear conventionally painted as brown dots here, but we can notice that the different provinces are painted with different hair color, with Sclavinia being darker than Germania and lighter than Gallia and Roma. This might make some sense, since Germanic peoples are thought to have originated in northern Germany/southern Scandinavia, and Slavs in C/E Europe (perhaps somewhere between Poland and Ukraine).

This raises the possibility that early Slavs were phenotypically somewhere in the middle of the European pigmentation continuum, although their exact position therein might only be determined with ancient DNA evidence. Today, the lighter-pigmented Slavs are probably those close to the Baltic (e.g., Russians and Poles), the darker ones from the Balkans, perhaps indicating different types of gene flow ("northern" Germanic/Baltic/Finno-Ugrian vs. "southern" Thraco-Illyrian-Greek).

If this is correct, then the slightly negative association of blue eyes in the present Czechs might be a culturally-transmitted vestige of inter-ethnic contact during the medieval period. A possible test would be to repeat the experiment with the Czechs' German neighbors, in which the process ought to operate in reverse -if my hypothesis is correct.

PLoS ONE 8(1): e53285. doi:10.1371/journal.pone.0053285

Trustworthy-Looking Face Meets Brown Eyes

Karel Kleisner et al.

We tested whether eye color influences perception of trustworthiness. Facial photographs of 40 female and 40 male students were rated for perceived trustworthiness. Eye color had a significant effect, the brown-eyed faces being perceived as more trustworthy than the blue-eyed ones. Geometric morphometrics, however, revealed significant correlations between eye color and face shape. Thus, face shape likewise had a significant effect on perceived trustworthiness but only for male faces, the effect for female faces not being significant. To determine whether perception of trustworthiness was being influenced primarily by eye color or by face shape, we recolored the eyes on the same male facial photos and repeated the test procedure. Eye color now had no effect on perceived trustworthiness. We concluded that although the brown-eyed faces were perceived as more trustworthy than the blue-eyed ones, it was not brown eye color per se that caused the stronger perception of trustworthiness but rather the facial features associated with brown eyes.

Link

How people get blue eyes

Genome-wide association studies can uncover links between genetic variants and phenotypes, even in the absence of any knowledge of how these links come about. All it takes is to make a statistical case linking genetic variation with the recorded phenotypic information.

This is somewhat unsatisfactory for a couple of reasons. First, we would like to know how cause and effect works, rather than simply observe that it does. Why do some people with certain genetic alleles have blue eyes?

Second, such functional studies allow us to predict phenotypes from genotypes. A great number of genetic mutations may cause particular phenotypes, and we are only able to discover associations between a subset of them that happens to exist in a population. Developing knowledge about function, rather than just statistical association, may help us in the future to infer the phenotypes of individuals from the deep past for which all non-osteological traces of phenotype have vanished, and may have been affected by genetic variants that are now extinct.

Many human traits are governed by a great number of genes, either through additive effects, or through complex interactions. Eye color is an example of a particular trait the genetic underpinnings of which in Caucasoids (other races have eyes that are uniformly brown) have been known for a while. Now a new study shows precisely how genetic mutations disrupt the formation of pigment in melanocytes, resulting in light-pigmented irides.


Genome Res doi:10.1101/gr.128652.111

HERC2 rs12913832 modulates human pigmentation by attenuating chromatin loop formation between a long-range enhancer and the OCA2 promoter

Mijke Visser et al.

Pigmentation of skin, eye and hair reflects some of the most evident common phenotypes in humans. Several candidate genes for human pigmentation are identified, and the SNP rs12913832 has strong statistical association with human pigmentation. It is located within an intron of the non-pigment gene HERC2, 21 kb upstream of the pigment gene OCA2, and the region surrounding rs12913832 is highly conserved among animal species. However, the exact functional role of HERC2 rs12913832 in human pigmentation is unknown. Here we demonstrate that the HERC2 rs12913832 region functions as an enhancer regulating OCA2 transcription. In darkly pigmented human melanocytes carrying the rs12913832 T-allele, we detected binding of the transcription factors HLTF, LEF1 and MITF to the HERC2 rs12913832 enhancer, and a long-range chromatin loop between this enhancer and the OCA2 promoter which leads to elevated OCA2 expression. In contrast, in lightly pigmented melanocytes carrying the rs12913832 C-allele, chromatin-loop formation, transcription factor recruitment and OCA2 expression are all reduced. Hence, we demonstrate that allelic variation of a common non-coding SNP located in a distal regulatory element not only disrupts the regulatory potential of this element but also affects its interaction with the relevant promoter. We provide the key mechanistic insight that allele-dependent differences in chromatin-loop formation (i.e. structural differences in the folding of gene loci) results in differences in allelic gene expression that affects common phenotypic traits. This concept is highly relevant for future studies aiming to unveil the functional basis of genetically-determined phenotypes including diseases.

Link

Iceman stories begin arriving!

The National Geographic has info, a teaser for an October 26 Nova special:

The genetic results add both information and intrigue. From his genes, we now know that the Iceman had brown hair and brown eyes and that he was probably lactose intolerant and thus could not digest milk—somewhat ironic, given theories that he was a shepherd. Not surprisingly, he is more related to people living in southern Europe today than to those in North Africa or the Middle East, with close connections to geographically isolated modern populations in Sardinia, Sicily, and the Iberian Peninsula. The DNA analysis also revealed several genetic variants that placed the Iceman at high risk for hardening of the arteries. ("If he hadn't been shot," Zink remarked, "he probably would have died of a heart attack or stroke in ten years.") Perhaps most surprising, researchers found the genetic footprint of bacteria known as Borrelia burgdorferi in his DNA—making the Iceman the earliest known human infected by the bug that causes Lyme disease.

It seems that my prediction that the Iceman will turn out to be Mediterranean in terms of his autosomal genetic components was right!

I don't get, however, how lactose intolerance is incompatible with being a shepherd, since milk is widely used in southern Europe both as a raw product and for its cheese. I lack the lactose tolerance gene myself, but that doesn't keep me from having a glass of milk nearly every day. Lactose tolerance makes it possible for people to drink lots of milk; lactose intolerance does not make it impossible for them to drink any, or to enjoy its secondary products (such as cheese and butter).

Blue-eyed attractiveness: stereotype and reality

Aesthetic Plast Surg. 2011 Aug 20. [Epub ahead of print]

The Blue-Eyes Stereotype: Do Eye Color, Pupil Diameter, and Scleral Color Affect Attractiveness?

Abstract
BACKGROUND:
Blue eyes have been the embodiment of attractiveness not only for decades but even for centuries. The primary aim of this study was to determine whether iridal color, particularly color blue, can increase the attractiveness of a person's eye area. As a secondary aim, the study examined the impact of pupil diameter and scleral color on the attractiveness of the eye area.

METHODS:
The stimulus material comprised images of the eye areas of 60 women ages 15-65 years. A total of 80 participants rated the attractiveness of each eye area on a 7-point Likert scale and estimated the age of the person. The color values of the iris and sclera were measured. As an additional subsample, 50% of the participants were asked what features of each eye area they found particularly appealing.

RESULTS:
Most surprisingly, no correlation was found between iridal color and rated attractiveness. However, the participants mentioned the color blue more often as a positive aspect than other iridal colors. A high inverse correlation was observed between attractiveness of the eye area and age. The larger the pupil diameter and the whiter the scleral color, the lower was the real and perceived age and the higher was the attractiveness.

CONCLUSION:
The data showed that the "blue-eyes stereotype" does exist. People consider blue eyes attractive, but in reality, blue is rated as attractive as other iridal colors. Bright scleral color and large pupils positively affect attractiveness because both features are significantly correlated with youthfulness.

Link

Brown-eyed Oetzi the Iceman

Heike Engel-21Lux / Sdtiroler Archologiemuseum / National Geographic Deutschland

Iceman Oetzi gets a new face for 20th anniversary

BOLZANO, Italy — Iceman Oetzi, whose mummified body was famously found frozen in the Italian Alps in 1991, will get a new face for the 20th anniversary of his discovery.

As part of a new exhibit at the South Tyrol Museum of Archaeology in Bolzano (www.iceman.it), two Dutch experts -- Alfons and Adrie Kennis -- have made a new model of the living Oetzi, this time with brown eyes.

Indeed, recent research has shown the Iceman, now approaching the tender age of 5,300 years, did not have blue eyes as previously believed.

The Kennis model was created based on three-dimensional images of the mummy's skeleton as well as the latest forensic technology, and will go on display on March 1 until January 15, 2012.

The Bolzano museum is also planning to improve conservation of the mummy by using pure nitrogen, which should help it keep its relatively young appearance by eliminating oxidation.

Oetzi was discovered on September 19, 1991 by a German couple in a glacier in the Oetztal Alps in South Tyrol, northern Italy.

The Iceman, who is believed to have died around the age of 45, was about 1.60 metres (5 foot, 3 inches) tall and weighed 50 kilogrammes (110 pounds), about average for his time. If he had lived today, he would have worn size 38 shoes.

But Oetzi's notoriety has also been linked to a supposed curse surrounding the mummy, after several people -- authors, researchers, even mountain guides -- who came in contact with it died over the years.

One of the couple who discovered Oetzi was found dead after a mountain hike in 2004. A forensic expert, who had closely examined the find, meanwhile died in a car accident in 1992 on his way to a lecture about Oetzi.

Picture from an Italian story on the same topic

Y chromosome and mtDNA of Louis XVI of France (?)

From the paper:

After the execution of Louis XVI in January 21st, 1793, eyewitnesses stated that many people from the crowd dipped their handkerchiefs in the king’s blood and kept these objects as mementos [8]. An Italian family has owned for more than a hundred years – as demonstrated by a letter addressed to the director of the Muse/ e Carnavalet in Paris, January 31st, 1900 – a dessicated gourd that presumably contained one of these handkerchiefs.

The mtDNA results:

the majority of the cloned sequences (87%) showed a rare N1b haplotype, with the substitutions 16093C-16145A-16176(G)-16223T. The same results were found in Bologna by direct sequencing, along with another substitution (16390G), not included in the amplicon generated in Barcelona. The haplotype found at the mtDNA HVR2(73G, 151T, 152C, 189G, 194T, 195C, 263G and 315.1C), is consistent with the N1b haplotype from the HVR1, although the substitutions 151T, 189G and 194T are not described in the current N1b dataset lineages. We interpret these three substitutions as additional, undescribed modifications of a N1b haplotype.

The Y-chromosome STR markers:

A ysearch query reveals a handful of distant (3 off in 9 markers) matches ranging from Anatolia to Scotland. Likewise yhrd turns up no matches using either the full or restricted panel, but a 1-off match with DYS389II-29 in the restricted panel in Marche, Italy.

Wikipedia tells me that Louis XVI's patrilineage goes all the way to Robert the Strong, and his matrilineage to Catherine of Mayenne.

One would think that a 1,000-year long line of kings and nobles would have left enough side branches and bastards along the way to register a few hits on the European map. Perhaps, that's a reason to stress the "presumed" in the paper's title. On the other hand, I find it interesting that the presumptive haplogroup of Louis XVI was G2a, the same as 2 of 5 warriors from Merovingian Bavaria (7th c. AD).

There is a way to authenticate the results, as the authors note:

At present it is not possible to prove genetically that the sample really belongs to the king Louis XVI. One possibility would be to extract a new sample from the dry heart attributed to the Dauphin Louis XVII, son of Louis XVI, preserved at the Basilique Saint-Denis in Paris, and compare both Y-chromosome profiles. Owing to the fact that the Y-chromosome profile found is not present in our current genetic databases such as YHRD, a potential match would directly authenticate the studied blood sample.

Forensic Sci Int Genet. 2010 Oct 10. [Epub ahead of print]

Genetic analysis of the presumptive blood from Louis XVI, king of France.

Lalueza-Fox C, Gigli E, Bini C, Calafell F, Luiselli D, Pelotti S, Pettener D.

Institut de Biologia Evolutiva, CSIC-UPF, Dr. Aiguader 88, 08003 Barcelona, Spain.

Abstract
A text on a pyrographically decorated gourd dated to 1793 explains that it contains a handkerchief dipped with the blood of Louis XVI, king of France, after his execution. Biochemical analyses confirmed that the material contained within the gourd was blood. The mitochondrial DNA (mtDNA) hypervariable region 1 (HVR1) and 2 (HVR2), the Y-chromosome STR profile, some autosomal STR markers and a SNP in HERC2 gene associated to blue eyes, were retrieved, and some results independently replicated in two different laboratories. The uncommon mtDNA sequence retrieved can be attributed to a N1b haplotype, while the novel Y-chromosome haplotype belongs to haplogroup G2a. The HERC2 gene showed that the subject analyzed was a heterozygote, which is compatible with a blue-eyed person, as king Louis XVI was. To confirm the identity of the subject, an analysis of the dried heart of his son, Louis XVII, could be undertaken.

Link

Brown-eyed men perceived to be more dominant

(Last Update June 21)

The authors discovered that males with brown eyes were considered more dominant than males with blue eyes, but when they altered their pictures to turn brown eyes into blue, the effect persisted. Thus, it is not the color itself that creates the impression of dominance, but rather other factors correlated with the brown-eyed phenotype.

One of these "other factors" could be chin breadth, which is known to be perceived as dominant. From the paper:

The question arises: why are brown-eyed males rated as more dominant than blue-eyed? Some facial features such as square jaws, thick eyebrows and broad cheekbones are linked with higher perceived dominance; facial submissiveness, on the other hand, is characterized by a round face with large eyes, smallish nose, and high eyebrows (Berry, 1990; Berry & Mcarthur, 1986; Cunningham,Barbee, & Pike, 1990; Mazur, Halpern, & Udry, 1994; Mueller & Mazur,1997; Thornhill & Gangestad, 1994). The morphological differences between blue-eyed and brown-eyed males were visualized by deformation of thin-plate splines (Fig. 3). In contrast with blue-eyed males, brown-eyed males have statistically broader and rather massive chins, broader (laterally prolonged) mouths, larger noses, and eyes that are closer together with larger eyebrows. In contrast, blue-eyed males show smaller and sharper chins, mouths that are laterally narrower, noses smaller, and a greater span between the eyes. Especially the broader massive chin, bigger nose, and larger eyebrows of brown-eyed males may explain their higher perceived dominance.

The authors propose that true genetic linkage between eye color and these other facial features is unlikely, as eye color is determined by few loci, and these are unlikely to be the same ones that influence these other facial features. Thus, they propose a different explanation, namely that blue-eyed and brown-eyed children are treated differently by their parents as they grow up, and this "different treatment" manifests itself phenotypically. The argument in favor of different treatment stems from the fact that many people are born blue-eyed, but their eye color is set to a darker shade eventually. The authors write:

It is possible that subjects with blue eyes are treated as a small child for a longer period than brown-eyed children. Such early social experience may have been literally ‘‘inscribed” into their faces, preserved until adulthood, and finally bring on the perception of higher submissiveness. Rosenberg and Kagan (1987, 1989) investigated the association between eye color and behavioral inhibition, revealing that children with blue eyes are more inhibited. Coplan et al. (1998) found a significant interaction between eye color and social wariness within preschoolers. Blueeyed males were rated as more socially wary, i.e. being more temperamentally inhibited, displaying more reticent behavior and having more internalizing problems, than males with brown eyes, though there were no differences between blue- and brown-eyed females (Coplan et al., 1998).

There is an alternative explanation, that requires neither genetic linkage nor an environmental factor such as upbringing. That factor is latent population structure.

In a truly long-term random mating population, and assuming that eye color is not genetically linked with e.g. chin breadth, then all combinations of chin breadth and eye color would occur with a probability determined entirely by the frequency of their genetic determinants in the population.

However, consider the possibility that the population is an incomplete mixture of a blue-eyed "facially submissive" population element, and a brown-eyed "facially dominant" one. If that was the case, then brown-eyed folks would tend to have dominant facial features by reason of their ancestry rather than any genetic linkage between the two traits.

As an analogy, consider a hypothetical population made up of Europeans and East Asians. Initially, there would be a statistical association between straight hair and short stature in the total population that would be entirely due to population structure rather than either pleiotropic effects of genes affecting both characters or genetic linkage of hair/stature genes.

The Czech population is intermediate in its bigonial diameter between Germans and Slovaks (its immediate neighbors) [1], they are also genetically intermediate between Germans and Slavs. Procopius noted in early medieval times that Slavs had intermediate pigmentation. So, I wouldn't discount the possibility that population structure due to incomplete blending may account for eye color/facial structure associations in this population.

UPDATE:

Here are some values for German and Czech males from [1].

Bigonial (go-go): 97.6 / 109.5

Nasal height (n-sn): 52 / 54.0

Nasal breadth (al-al): 34.0 / 36.2

Mouth breadth (ch-ch): 50.9 / 53.8

Intercanthal distance (en-en): 31.2/30.9

Unfortunately there is no data for the eyebrows, but all of the above differences are in the expected direction under my theory: Germans have narrower jaws, smaller noses, narrower mouths, and eyes placed further apart than Czechs.

So, I think it is quite likely that the blue-eyed facially submissive type found in this sample may have a German origin.

PS: I did an average of the blue- and brown-eyed averages for reference:

[1] International anthropometric study of facial morphology in various ethnic groups/races, Leslie G Farkas, J Craniofac Surg 16:615-46

Personality and Individual Differences
Volume 49, Issue 1, July 2010, Pages 59-64

Eye color predicts but does not directly influence perceived dominance in men

Karel Kleisner et al.

This study focuses on the relationship between eye color, gender, and psychological characteristics perceived from the human face. Photographs of 40 male and 40 female students were rated for perceived dominance and attractiveness. Attractiveness showed no relation with eye color. In contrast, eye color had a significant effect on perceived dominance in males: brown-eyed men were rated as more dominant than men with blue eyes. To control for the effect of eye color, we studied perceived dominance on the same photographs of models after changing the iris color. The eye color had no effect on perceived dominance. This suggests that some other facial features associated with eye color affect the perception of dominance in males. Geometric morphometrics have been applied to reveal features responsible for the differences in facial morphospace of blue-eyed and brown-eyed males.

Link

Predicting Phenotype from Genotype: Normal Pigmentation (Valenzuela et al. 2010)

Yann Klimentidis points me to this new paper on predicting human pigmentation phenotype from genotype. The paper is interesting in view of the recent finding that lactose intolerance phenotype is not very well captured by the known genetic variation.

The current paper looks at how well normal pigmentation (skin, hair, and eye color) is predicted from known genotypes. The sample consists of individuals from the University of Arizona.

From the paper:

The three most frequent SNPs found in the range from the highest R² model to the first inflection of the graph were used to construct an MLR model for each trait. These models accounted for significant variation in each of the four measured traits: scalp-hair total melanin (76.3%), natural log of the ratio of eumelanin-to-pheomelanin (43.2%), skin reflectance (45.7%), and eye color (74.8%) (Table 3).

Obviously two caveats should be raised:

(i) that the associations are dependent on the sample. It is not clear how the percentage of variation explained would be altered in a population of different ethnic origins -not represented in the UoA.

(ii) that the associations may be mediated by other genetic factors, not yet discovered.

With respect to (ii), pigmentation appears to be a "success story" of genome-wide association studies, as a relatively small number of SNPs accounts for such a high level of variation (about 3/4 for the best traits). However, the missing 1/4 should also make us cautious when we attempt to infer the pigmentation of a sample, in either a forensic or an archaeological context.

Journal of Forensic Science doi:10.1111/j.1556-4029.2009.01317.x

Predicting Phenotype from Genotype: Normal Pigmentation

Robert K. Valenzuela et al.

Abstract

Genetic information in forensic studies is largely limited to CODIS data and the ability to match samples and assign them to an individual. However, there are circumstances, in which a given DNA sample does not match anyone in the CODIS database, and no other information about the donor is available. In this study, we determined 75 SNPs in 24 genes (previously implicated in human or animal pigmentation studies) for the analysis of single- and multi-locus associations with hair, skin, and eye color in 789 individuals of various ethnic backgrounds. Using multiple linear regression modeling, five SNPs in five genes were found to account for large proportions of pigmentation variation in hair, skin, and eyes in our across-population analyses. Thus, these models may be of predictive value to determine an individual’s pigmentation type from a forensic sample, independent of ethnic origin.

Link

Y chromosome, mtDNA, and eye color of Nicolaus Copernicus

The identification of Copernicus was made possible by typing DNA from hair found in a book he owned and matching it with DNA from his putative remains.

Copernicus belonged to mtDNA haplogroup H:

In addition to the hypervariable region analysis, 16 haplogroup informative SNP positions were examined (709G, 1719G, 1811A, 3010G, 6365T, 6776T, 7028C, 8251G, 8697G, 9055G,11251A, 12372G, 13708G, 14766C, 14798T, and 15904C). Analysis of these haplogroup informative mtDNA polymorphisms indicates that the examined individual belongs to haplogroup H, which is the most frequent of the 6 European-specific haplogroups.

His Y-STR haplotype was also determined:

Male sex was further confirmed by the analysis of 16 STR loci located on Y chromosome included in the Yfiler amplification kit (Applied Biosystems): DYS456– 16; DYS389I– 13; DYS390– 23; DYS389II– 29; DYS458– 19; DYS19– 14; DYS385– 11, 13; DYS393– 13; DYS391– 11; DYS439– 12; DYS635– 23; DYS392–13; Y GATA H4– 12; DYS437– 15; DYS438– 12; DYS448– 19.

...

In the case of the paternal lineage, the search of the YHRD Y chromosome population database (19) did not reveal the haplotype found in the examined human remains among the 2,595 complete haplotypes comprising the Eurasian metapopulation
and among all of the 10,243 complete haplotypes included in the database originating from all over the world. The YHRD database size varies significantly based on the number and character of loci that are included in the search profile. By limiting their
number to the core set called the minimal haplotype (most often analyzed Y-STR loci) the searchable data in the YHRD database were significantly extended, giving the total number of 63,369 haplotypes. In this larger dataset, a minimal Y-chromosomal haplotype, derived from the putative Copernicus remains, was present 47 times, 44 times in a European metapopulation consisting of 31,762 minimal Y-chromosome haplotypes. The same haplotype has been found in individuals from many countries, including Austria, Germany, Poland, and the Czech Republic.

Copernicus' haplotype places him almost certainly in haplogroup R1b. While this haplogroup has a very wide distribution, it is the case that it is one of the haplogroups which differentiate Germans from Poles. So, while this is insufficient to ascertain the ethnic origin of Copernicus' patrilineage, it certainly suggests a higher probability for it being of ethnic German rather than Polish origin.

The researchers also estimated the astronomer's eye color:

Analysis of the SNP position located in the HERC2 revealed the homozygous C/C genotype, which is the predominant genotype among blue or gray-eyed humans (≈80%). This genotype is rare among people with dark iris coloration (8, 20, 21). The result indicates that Copernicus might have had light iris color, a finding that is rather unexpected given that he is usually shown in portraits with dark eyes. Nevertheless, it is difficult to unambiguously interpret this finding because, although it is significantly less probable, the genotype C/C in rs12913832 can be associated with dark (but not brown/black) irises.

The frequency of blue eyes for the C/C genotype is from a recent study by Polish researchers, so the odds are fairly good that the inference of a non-dark eyed phenotype for Copernicus is genuine.

UPDATE: The Spittoon's coverage of this study erroneously claims that Copernicus:

is best known for being the first to propose that the Earth circles the sun, and not the other way around.

In fact, the first to propose the heliocentric theory was Aristarchus of Samos, a 4th c. BC Greek astronomer, 18 centuries before Copernicus.

PNAS doi:10.1073/pnas.0901848106

Genetic identification of putative remains of the famous astronomer Nicolaus Copernicus

Wiesław Bogdanowicz et al.

Abstract

We report the results of mitochondrial and nuclear DNA analyses of skeletal remains exhumed in 2005 at Frombork Cathedral in Poland, that are thought to be those of Nicolaus Copernicus (1473–1543). The analyzed bone remains were found close to the altar Nicolaus Copernicus was responsible for during his tenure as priest. The mitochondrial DNA (mtDNA) profiles from 3 upper molars and the femurs were identical, suggesting that the remains originate from the same individual. Identical mtDNA profiles were also determined in 2 hairs discovered in a calendar now exhibited at Museum Gustavianum in Uppsala, Sweden. This calendar was the property of Nicolaus Copernicus for much of his life. These findings, together with anthropological data, support the identification of the human remains found in Frombork Cathedral as those of Nicolaus Copernicus. Up-to-now the particular mtDNA haplotype has been observed only 3 times in Germany and once in Denmark. Moreover, Y-chromosomal and autosomal short tandem repeat markers were analyzed in one of the tooth samples, that was much better preserved than other parts of the skeleton. Molecular sex determination revealed that the skeleton is from a male individual, and this result is consistent with morphological investigations. The minimal Y-chromosomal haplotype determined in the putative remains of Nicolaus Copernicus has been observed previously in many countries, including Austria, Germany, Poland, and the Czech Republic. Finally, an analysis of the SNP located in the HERC2 gene revealed the C/C genotype that is predominant in blue-eyed humans, suggesting that Copernicus may have had a light iris color.

Link

More on prehistoric South Siberians (Keyser et al. 2009)

This seems like a compendium of these authors' previous work (see here and links therein) which had appeared in forensic journals so far; there seems to be more material in this paper than in the previous shorter papers, but as far as I can tell, no new genetic results.

There is also supplementary data in the article.

From the paper:

The additional analysis performed on Xiongnu specimens revealed that whereas none of the specimens from the Egyin Gol valley bore this haplogroup, the Scytho-Siberian skeleton from the Sebÿstei site exhibited R1a1 haplogroup.

A previous study on Egyin Gol from Mongolia by Keyser et al.

More from the paper:

A search in the YHRD database as well as in our own databank revealed that none of the Y-STR haplotypes obtained from the south Siberian samples perfectly matched (at 17 loci) those included in the databases. Nevertheless, when not all loci were scored, matches were found for all samples except two (S07 and S32) for which even the search based on the 9-loci minimal haplotype was fruitless (Table 4).

The article includes fairly comprehensive searches of the discovered Y-chromosome and mtDNA types in modern populations.

The mtDNA results:

Twenty samples were found to belong to west Eurasian haplogroups (U2, U4,
U5a1, T1, T3, T4, H5a, H6, HV, K, and I), whereas the 6 remaining samples were attributed to east Eurasian haplogroups (Z, G2a, C, F1b and N9a).

Interestingly:

Moreover, it is likely that some mtDNA lineages were carried to southern Siberia from the Volga–Ural region. Incidentally, in the fifth century BC, Herodotus mentioned transit trade occurring in Central Asia along a route that stretched from the Urals in the west to the Altai and the Minusinsk Basin in the east (Hemphill and Mallory 2004). In Altai, the presence of the R1a1 haplogroup in the middle of the fifth century BC is confirmed by the sample SEB 96K2 of Ricaut et al. (2004) which was found to belong to this Y-haplogroup. The boundary of the eastern European influence seems to be fixed at the peri-Baikal area since no R1a1 haplogroup was found in the Xiongnu specimens of the Northern border of Mongolia.

Link to Ricaut et al. (2004). This is in good agreement with the anthropological picture by Alexeev:

"The boundary of the Europeoid movement is clearly fixed at Lake Baikal. To the east of Baikal no palaeoanthropological find bears any traces of Europeoid admixture."

See also my compendium on ancient Y-chromosome studies.

Human Genetics doi:10.1007/s00439-009-0683-0

Ancient DNA provides new insights into the history of south Siberian Kurgan people.

Keyser C. et al.

Abstract

To help unravel some of the early Eurasian steppe migration movements, we determined the Y-chromosomal and mitochondrial haplotypes and haplogroups of 26 ancient human specimens from the Krasnoyarsk area dated from between the middle of the second millennium BC. to the fourth century AD. In order to go further in the search of the geographic origin and physical traits of these south Siberian specimens, we also typed phenotype-informative single nucleotide polymorphisms. Our autosomal, Y-chromosomal and mitochondrial DNA analyses reveal that whereas few specimens seem to be related matrilineally or patrilineally, nearly all subjects belong to haplogroup R1a1-M17 which is thought to mark the eastward migration of the early Indo-Europeans. Our results also confirm that at the Bronze and Iron Ages, south Siberia was a region of overwhelmingly predominant European settlement, suggesting an eastward migration of Kurgan people across the Russo-Kazakh steppe. Finally, our data indicate that at the Bronze and Iron Age timeframe, south Siberians were blue (or green)-eyed, fair-skinned and light-haired people and that they might have played a role in the early development of the Tarim Basin civilization. To the best of our knowledge, no equivalent molecular analysis has been undertaken so far.

Link

Light-pigmented Caucasoids from prehistoric Siberia

This sample was previously tested for Y-chromosome and mtDNA polymorphisms.

The pigmentation-related loci tested can be seen in the labels of my post, which should lead you to some earlier studies on them.

Most individuals were found to be most similar to European than to East Asian or African individuals based on these loci, although some (2 from Andronovo) of them were more similar to East Asians or intermediate (1 from Tagar) between East Asians and Europeans.

Interestingly, 1 of the Andronovo Mongoloids (S07) was previously found to belong to Y chromosome haplogroup C(xC3), while the Caucasoid-Mongoloid individual from Tagar (S32) belonged to haplogroup R1a1.

It should be noted that the use of the term "European individual ancestry" does not mean that these individuals were from Europe, as no test to distinguish between European and Asian Caucasoids was performed, and we know from literary descriptions and occasional archaeological remains about the ancient presence of light-pigmented Caucasoids in Siberia.

From the paper:

The genotype for rs12913832 was obtained for 23 out of the 25 samples, and most had the G/G genotype (n=15), which indicates that at least 60% of ancient specimens were probably blue- or green-eyed individuals. The remaining samples had the A/G (n=5) or A/A (n=3) genotypes, which are predictive of brown eye color phenotype.

International Journal of Legal Medicine doi:10.1007/s00414-009-0348-5

Pigment phenotype and biogeographical ancestry from ancient skeletal remains: inferences from multiplexed autosomal SNP analysis

Caroline Bouakaze et al.

Abstract

In the present study, a multiplexed genotyping assay for ten single nucleotide polymorphisms (SNPs) located within six pigmentation candidate genes was developed on modern biological samples and applied to DNA retrieved from 25 archeological human remains from southern central Siberia dating from the Bronze and Iron Ages. SNP genotyping was successful for the majority of ancient samples and revealed that most probably had typical European pigment features, i.e., blue or green eye color, light hair color and skin type, and were likely of European individual ancestry. To our knowledge, this study reports for the first time the multiplexed typing of autosomal SNPs on aged and degraded DNA. By providing valuable information on pigment traits of an individual and allowing individual biogeographical ancestry estimation, autosomal SNP typing can improve ancient DNA studies and aid human identification in some forensic casework situations when used to complement conventional molecular markers.

Link

Interaction between loci affecting human pigmentation in Poland

Annals of Human Genetics doi:10.1111/j.1469-1809.2009.00504.x

Interactions Between HERC2, OCA2 and MC1R May Influence Human Pigmentation Phenotype

Wojciech Branicki et al.

Abstract

Human pigmentation is a polygenic trait which may be shaped by different kinds of gene–gene interactions. Recent studies have revealed that interactive effects between HERC2 and OCA2 may be responsible for blue eye colour determination in humans. Here we performed a population association study, examining important polymorphisms within the HERC2 and OCA2 genes. Furthermore, pooling these results with genotyping data for MC1R, ASIP and SLC45A2 obtained for the same population sample we also analysed potential genetic interactions affecting variation in eye, hair and skin colour. Our results confirmed the association of HERC2 rs12913832 with eye colour and showed that this SNP is also significantly associated with skin and hair colouration. It is also concluded that OCA2 rs1800407 is independently associated with eye colour. Finally, using various approaches we were able to show that there is an interaction between MC1R and HERC2 in determination of skin and hair colour in the studied population sample.

Link