Since the mid-20th century, ‘skin bleaching’ has become more and more common among dark-skinned populations. It involves lightening skin color by means of topical preparations that contain hydroquinone, cortisone, or mercury. These products are effective, but prolonged use may damage the skin by making the epidermis thinner and by breaking down collagen fibers. Despite being condemned by the medical profession and increasingly restricted by governments, they can easily be obtained in various places: hair-stylist salons, subway stations, African public markets, etc.
Skin bleachers seem to be used the most in South Asia and its diaspora. Next come sub-Saharan Africa and its diaspora (West Indies, Brazil, United States, Western Europe, etc.), the Philippines and elsewhere in Asia. The market is mainly young and female. Thus, rate of use is 61.4% among Surinamese women of Indian origin less than 26 years old, as compared to 13.1% among young Surinamese of other origins (Javanese, African, etc.) (Menke, 2002).
In Africa, rate of use is 25% in Bamako, Mali, up to 52% in Dakar, Senegal, up to 35% in Pretoria, South Africa, and up to 77% in Lagos, Nigeria (Ntambwe, 2004). The practice has become so widespread that it has been nicknamed maquillage – ‘make-up’ (Ondongo, 1984). According to one African specialist, men encourage it by considering light-skinned women to be more attractive, intelligent, moral, desirable, and chaste. In contrast, dark-skinned women are said to look mean, evil, stupid, and untrustworthy (Ntambwe, 2004). This opinion is consistent with the results of a survey among Ghanaian women. Most of the respondents thought that men prefer light skin in a woman: “Sometimes if you really want to marry a particular man, you have to bleach” (Fokuo, 2009)
In Jamaica, users do not seem motivated by shame of their Black identity. Surveys show them having as much racial self-esteem as non-users. The motivation is more to make one’s face ‘cool’, to imitate one’s peers, to look pretty and attract a partner, and to feel good about oneself. There is also the influence of popular culture, such as Eurocentric beauty contests and singers who glorify women with light brown skin. In the dance-hall song Browning, Buju Banton says he loves his light-skinned girlfriend, his ‘browning’, more than his car, his motorbike, and his money. In Bleach On, Captain Barkey tells girls to keep on bleaching their skin (Charles, 2009).
Strangely, these products have become increasingly popular among South Asians, Africans, and West Indians for the past half-century, yet the same period has also seen these peoples regain much of their cultural independence. In advertising, magazines, or TV serials, one sees many more women from the local population than there were before.
Actually, it’s not so strange. Back when the local media recycled images of women from Western sources, the female audience had trouble identifying with them; there was a gap between the two. Because these images are now adapted to the local reality, they project a stronger normative influence on local women, who are keener to imitate them. These women, however, are still darker-skinned than the somatic norm being projected. This is especially so with Indian ‘Bollywood’ films but is also the case with serial dramas in Latin America and the Arab world.
References
Charles, C.A.D. (2009). Skin bleachers’ representations of skin color in Jamaica, Journal of Black Studies, 40, 153-170.
Charles, C.A.D. (2003). Skin bleaching, self-hate, and Black identity in Jamaica, Journal of Black Studies, 33, 711-728.
Fokuo, J. Konadu. (2009). The lighter side of marriage: Skin bleaching in post-colonial Ghana, Research Review NS, 25(1), 47-66.
Menke, J. (2002). Skin bleaching in multi-ethnic and multicolored societies. The case of Suriname, paper presented to the CSA Conference, Nassau, Bahamas, May 27 – June 1, 2002, Coping with Challenges, Contending with Change.
http://www.colorfoundation.org/pdf/skin%20bleach%20Sur%20CSA%20220502.doc
Ntambwe, M. (2004), 'Mirror mirror on the wall, who is the FAIREST of them all?' Science in Africa, March. http://www.scienceinafrica.co.za/2004/march/skinlightening.htm
Ondongo, J. (1984), Noir ou blanc ? Le vécu du double dans la pratique du « maquillage » chez les Noirs, Nouvelle Revue d’Ethnopsychiatrie, 2, 37-65.
Thursday, November 19, 2009
Thursday, November 12, 2009
Lévi-Strauss and gene-culture co-evolution
With the recent death of Claude Lévi-Strauss, there has been an outpouring of praise for his contributions to anthropology, notably the struggle for a more politically conscious anthropology and the shift from biological determinism to cultural determinism. This praise tells us more about the praisers than about Lévi-Strauss himself. In truth, he scarcely resembled the image presented in most of his obituaries, having denounced in his book Tristes tropiques the intrusion of a “utopian spirit” into his field.
He is clearly referring here to the concept of gene-culture co-evolution. But just what are these genetic traits that cultures have shaped differently in different human populations? He doesn’t seem to mean minor physiological processes, like an improved ability to digest milk or carbohydrates. In fact, he seems to be referring to mental and behavioral traits, especially when he mentions ‘ideas of morality’. Is he saying that there has been selection for differences in moral capacity among human populations?
And if cultures have shaped different gene pools differently wouldn’t these gene pools be ‘races’? Did Lévi-Strauss think through this line of thought? Perhaps in denying the race concept he was simply making the kind of ritual denunciation that most anthropologists make … and only half-believe.
It is probably too late to find out what he really meant. This is not a line of thought that he seems to have pursued in his other publications, at least none I am aware of.
References
Lévi-Strauss, C. (1985). Claude Lévi-Strauss à l’université Laval, Québec (septembre 1979), prepared by Yvan Simonis, Documents de recherche no. 4, Laboratoire de recherches anthropologiques, Département d’anthropologie, Faculté des Sciences sociales, Université Laval.
Lévi-Strauss, C., (1955). Tristes tropiques, Paris.
With a shelter of legalistic and formalistic rationalism, we similarly build an image of the world and society where all problems can be settled by a courtroom approach whose logic is artful maneuvering, and we do not realize that the universe is no longer composed of what we are talking about.
Nor was he a complete cultural determinist. Like many thinkers of his generation, he felt that culture has contributed just as much as biology to differences among human populations. This is not, however, the same as believing that biology has created only skin-deep differences. He made this clear in a speech at our university in 1979:
… I would not feel truly anthropologist or structuralist if I did not accept that all questions should be discussed, and the question of the respective share of nature and nurture in human culture seems to me one of the most important ones we can and ought to ask ourselves. This issue has been made sterile for years and years by the false categorizations of physical anthropology related to the belief in the existence of human races.
However, we must not forget that, as anthropologists, the aspects of the question that will always appeal to us will be much less the genetic determination of culture or cultures than the cultural determination of genetics. By this I mean that a culture always will be made much less by its members’ gene pool than it will contribute to shaping and altering this gene pool.
The selection pressure of culture—the fact that it favors certain types of individuals rather than others through its forms of organization, its ideas of morality, and its aesthetic values—can do infinitely more to alter a gene pool than the gene pool can do to shape a culture, all the more so because a culture’s rate of change can certainly be much faster than the phenomena of genetic drift. (Lévi-Strauss, 1979, p. 24-25)
He is clearly referring here to the concept of gene-culture co-evolution. But just what are these genetic traits that cultures have shaped differently in different human populations? He doesn’t seem to mean minor physiological processes, like an improved ability to digest milk or carbohydrates. In fact, he seems to be referring to mental and behavioral traits, especially when he mentions ‘ideas of morality’. Is he saying that there has been selection for differences in moral capacity among human populations?
And if cultures have shaped different gene pools differently wouldn’t these gene pools be ‘races’? Did Lévi-Strauss think through this line of thought? Perhaps in denying the race concept he was simply making the kind of ritual denunciation that most anthropologists make … and only half-believe.
It is probably too late to find out what he really meant. This is not a line of thought that he seems to have pursued in his other publications, at least none I am aware of.
References
Lévi-Strauss, C. (1985). Claude Lévi-Strauss à l’université Laval, Québec (septembre 1979), prepared by Yvan Simonis, Documents de recherche no. 4, Laboratoire de recherches anthropologiques, Département d’anthropologie, Faculté des Sciences sociales, Université Laval.
Lévi-Strauss, C., (1955). Tristes tropiques, Paris.
Thursday, November 5, 2009
Was Roman Britain multiracial?
Historians often assume that the Romans changed Britain politically but not demographically. The indigenous elites adopted Roman culture while the mass of the population remained Celtic. When the Anglo-Saxons arrived in the fifth century, much of this population fled to Wales and Cornwall, where they would retain their language and traditions. Meanwhile, those who remained behind were obliterated through a process of ethnic cleansing and coerced assimilation.
This historical account may be false. First, the Roman occupation seems to have brought profound demographic change. This has been suspected for some time on the basis of unusual burial objects and epigraphic inscriptions that record the presence of individuals from throughout the Roman Empire. Now, after analyzing remains from two burial grounds near Roman York, a research team has concluded that the buried individuals had diverse geographic origins (Leach et al., 2009). In particular, the craniometric data revealed many of sub-Saharan or Egyptian origin. At the ‘Trentholme Drive’ burial ground, 66% clustered most closely with Europeans, 23% with sub-Saharan Africans, and 11% with Egyptians. At the ‘Railway’ burial ground, the proportions were 53% European, 32% sub-Saharan, and 15% Egyptian.
York was a legionary fortress, so these individuals may have been legionnaires. There are, in fact, epigraphic references to African soldiers and even a written account about one in a history of the Emperor Septimius Severus (146-211 AD) (Scriptores Historiae Augustae, p. 425).
Why were these Africans so far from home? In the case of the Egyptians, Rome thought it unwise to station soldiers among people of the same ethnic background. The temptation would be strong to side with the locals if a rebellion occurred. In the case of the sub-Saharan Africans, they were recruited into the army for the same reason that Germanic barbarians were recruited: Rome could not meet its manpower requirements solely from within its empire. There was also a perception that the Romans had become soft and that barbarians made better soldiers.
Finally, Rome, like many multi-national empires, had a policy of moving people around in order to promote a common identity and to eliminate ethnic distinctiveness. The Assyrians had perfected this policy, e.g., the deportation of the Jews to Babylon and their replacement by other peoples. The Roman authorities used their army to this end. They wished to create an atomized society where regionalism or ethnicity could not mobilize resistance to imperial rule.
It is likely that these legionnaires had a major demographic impact wherever they were stationed, especially if we include the many officials, petty functionaries, traders, and others who came in their wake. Much of Roman Britain thus seems to have been Romanized in culture and multiethnic in origin.
This, in turn, calls for a few other reinterpretations. Wales and Cornwall are not Celtic-speaking today because they took in Romano-British refugees fleeing Anglo-Saxon invaders. They were simply those parts of Britain that had remained Celtic in language, culture, and population. The rest—present-day England—had long become heavily Romanized and cosmopolitan.
Nor do we have to postulate a process of ethnic cleansing and coerced assimilation to explain the extinction of Roman Britain in the 5th and 6th centuries. As Seccombe (1992) points out, the Roman Empire suffered from negative population growth. Not enough people married and had children to offset relatively high mortality among infants and young adults. In breaking down local collective identities, whether ethnic or regional, the Empire had created an atomized and increasingly anonymous society without the carrots and sticks that tightly knit societies use to push individuals down the path of family formation.
Once Rome had pulled its troops out of Britain in the early 5th century, there was no longer an inflow of people to offset the demographic deficit. The local population fell into decline, and the decline accelerated in the 6th century when plagues killed three out of every ten people. The Romano-British needed no help from the Anglo-Saxons to die out. They did it largely on their own.
References
Leach, S., M. Lewis, C. Chenery, G. Müldner, & H. Eckardt. (2009). Migration and diversity in Roman Britain: A multidisciplinary approach to the identification of immigrants in Roman York, England, American Journal of Physical Anthropology, 140, 546-561.
Scriptores Historiae Augustae – Septimius Severus 22:4-6, transl. D. Magie (1922-1932) Vol 1, London: Heinemann.
Seccombe, W. (1992). A Millennium of Family Change. London: Verso.
This historical account may be false. First, the Roman occupation seems to have brought profound demographic change. This has been suspected for some time on the basis of unusual burial objects and epigraphic inscriptions that record the presence of individuals from throughout the Roman Empire. Now, after analyzing remains from two burial grounds near Roman York, a research team has concluded that the buried individuals had diverse geographic origins (Leach et al., 2009). In particular, the craniometric data revealed many of sub-Saharan or Egyptian origin. At the ‘Trentholme Drive’ burial ground, 66% clustered most closely with Europeans, 23% with sub-Saharan Africans, and 11% with Egyptians. At the ‘Railway’ burial ground, the proportions were 53% European, 32% sub-Saharan, and 15% Egyptian.
York was a legionary fortress, so these individuals may have been legionnaires. There are, in fact, epigraphic references to African soldiers and even a written account about one in a history of the Emperor Septimius Severus (146-211 AD) (Scriptores Historiae Augustae, p. 425).
On another occasion, when he was returning to his nearest quarters from an inspection of the wall at Luguvallium (Carlisle) in Britain, at a time when he had not only proved victorious but had concluded a perpetual peace, just as he was wondering what omen would present itself, an Ethiopian soldier, who was famous among buffoons and always a notable jester, met him with a garland of cypress-boughs. And when Severus in a rage ordered that the man be removed from his sight, the Ethiopian by way of jest cried, it is said, “You have been all things, now, O conqueror, be a god.”
Why were these Africans so far from home? In the case of the Egyptians, Rome thought it unwise to station soldiers among people of the same ethnic background. The temptation would be strong to side with the locals if a rebellion occurred. In the case of the sub-Saharan Africans, they were recruited into the army for the same reason that Germanic barbarians were recruited: Rome could not meet its manpower requirements solely from within its empire. There was also a perception that the Romans had become soft and that barbarians made better soldiers.
Finally, Rome, like many multi-national empires, had a policy of moving people around in order to promote a common identity and to eliminate ethnic distinctiveness. The Assyrians had perfected this policy, e.g., the deportation of the Jews to Babylon and their replacement by other peoples. The Roman authorities used their army to this end. They wished to create an atomized society where regionalism or ethnicity could not mobilize resistance to imperial rule.
It is likely that these legionnaires had a major demographic impact wherever they were stationed, especially if we include the many officials, petty functionaries, traders, and others who came in their wake. Much of Roman Britain thus seems to have been Romanized in culture and multiethnic in origin.
This, in turn, calls for a few other reinterpretations. Wales and Cornwall are not Celtic-speaking today because they took in Romano-British refugees fleeing Anglo-Saxon invaders. They were simply those parts of Britain that had remained Celtic in language, culture, and population. The rest—present-day England—had long become heavily Romanized and cosmopolitan.
Nor do we have to postulate a process of ethnic cleansing and coerced assimilation to explain the extinction of Roman Britain in the 5th and 6th centuries. As Seccombe (1992) points out, the Roman Empire suffered from negative population growth. Not enough people married and had children to offset relatively high mortality among infants and young adults. In breaking down local collective identities, whether ethnic or regional, the Empire had created an atomized and increasingly anonymous society without the carrots and sticks that tightly knit societies use to push individuals down the path of family formation.
Once Rome had pulled its troops out of Britain in the early 5th century, there was no longer an inflow of people to offset the demographic deficit. The local population fell into decline, and the decline accelerated in the 6th century when plagues killed three out of every ten people. The Romano-British needed no help from the Anglo-Saxons to die out. They did it largely on their own.
References
Leach, S., M. Lewis, C. Chenery, G. Müldner, & H. Eckardt. (2009). Migration and diversity in Roman Britain: A multidisciplinary approach to the identification of immigrants in Roman York, England, American Journal of Physical Anthropology, 140, 546-561.
Scriptores Historiae Augustae – Septimius Severus 22:4-6, transl. D. Magie (1922-1932) Vol 1, London: Heinemann.
Seccombe, W. (1992). A Millennium of Family Change. London: Verso.
Thursday, October 29, 2009
Are we all Middle Easterners now?
Dienekes is arguing that Middle Eastern farmers demographically replaced Europe’s original population between 8,000 and 3,000 years ago. This argument seems to be proven by two recent papers that show no genetic continuity between Europe’s late hunter-gatherers and early farmers. The continent’s current gene pool seems to owe very little to the original Upper Paleolithic and Mesolithic inhabitants. So goes his argument.
This argument raises one obvious problem. It implies that the physical characteristics of Europeans, especially northern Europeans, arose recently and over a short time.
How short? As late as 7500 years ago, hunter-fisher-gatherers still inhabited Europe above a line running from the Netherlands to the Black Sea. The line then gradually moved north, reaching northern Germany about 5500 BP and the eastern and northern agricultural areas of Scandinavia around 4300 BP. This leaves very little time for the evolution of the northern European phenotype, i.e., lightening of the skin to pinkish-white and diversification of hair and eye color into a wide range of hues. This phenotype is attested by historical records going back over two thousand years, so we’re left with a time window of less than five thousand years.
Is that enough time for so much phenotypic change? Perhaps, but the selection pressures would have to be very strong.
Let’s turn to the first of the two papers. Bramanti et al. (2009) compared mtDNA sequences from late hunter-gatherers and early farmers who had lived in northern and central Europe (Lithuania, Poland, Russia, Germany). There was no evidence of genetic continuity between the two populations.
But this paper raises several other points:
1. Modern Europeans are almost as distant genetically from the early farmers as they are from the late hunter-gatherers. To be ancestral to modern Europeans, these farmers and their descendents would need a very low female population size (less than 3,000 individuals). As the authors admit, this figure is well below current archaeological estimates (124,000 individuals).
2. The sample sizes are very small for the early farmers (25 individuals) and the late hunter-gatherers (20 individuals).
3. The sample of late hunter-gatherers covers a much longer time frame (15,400 – 4300 BP) than does the sample of early farmers (7650 - 7400 BP).
In sum, the authors have tried to describe the gene pool of late European hunter-gatherers with data from 20 individuals spread over four countries and over some 11,000 years.
Can such a sample be representative? Doubtful. Besides the smallness of the sample, the late hunter-gatherers were not a homogeneous population. By their time, Europe had completely changed ecologically. Open tundra had given way to forest and it was no longer possible to hunt wandering herds of reindeer. Hunter-gatherers now lived in smaller and more localized groups. Each group would have had its own genetic profile as a result of genetic drift and founder effects.
Even if these 20 individuals fairly represented late hunter-gatherers, the genetic continuity hypothesis is not disproved by genetic differences between them and early farmers. Undoubtedly, some hunter-gatherers adopted farming earlier than others and thus contributed more to the early farmer gene pool. Others never adopted farming and thus contributed nothing. Founder effects would have been considerable.
There are thus two serious problems with Bramanti et al. (2009):
1. The sample of late hunter-gatherers is too small and too scattered over space and time to be representative of the late hunter-gatherer gene pool;
2. The genetic continuity hypothesis does not assume that the early farmer gene pool was a representative cross-section of the late hunter-gatherer gene pool.
Let’s turn to the other paper. Malmström et al. (2009) retrieved mtDNA from 19 late hunter-gatherers and 3 early farmers who lived in southern Scandinavia. The late hunter-gatherers show no genetic continuity with the early farmers or with modern Scandinavians but they do show genetic continuity with modern Baltic populations (i.e., Latvians). This seems consistent with archaeological evidence that the eastern Baltic was a refugium for Europe’s last hunter-gatherers. Indeed, the inland boundaries of Latvia, Lithuania, and Old Prussia may hark back to a time when these people fished and sealed from coastal stations part of the year and then moved some distance inland to hunt game the rest of the year.
This study has the merit of being more narrowly focused in time and space. Like the other study, however, it suffers from very small sample sizes and the likelihood of founder effects. In fact, the early farmer sample is so small that genetic continuity with modern Scandinavians is unsure.
What now?
The challenge now will be to enlarge this sample of late hunter-gatherers. By ‘enlarge’, I don’t simply mean a larger sample. I also mean a larger number of geographic locations to be sampled. Late hunter-gatherers were a heterogeneous bunch. Some contributed a lot to the future gene pool. Others went extinct.
The ‘losers’ were small inland hunting bands with low population densities. They were less able to integrate agriculture into their nomadic way of life and also more likely to retreat in the face of much larger farming communities.
The ‘winners’ were semi-sedentary coastal groups with relatively high population densities. Because such groups depended more on fishing and sealing than on hunting and gathering, they could more readily integrate farming into their lifestyle, if only as a secondary subsistence activity. They were also more numerous and likelier to withstand encroachment by farming communities.
References
Bramanti, B., M.G. Thomas, W. Haak, M. Unterlaender, P. Jores, K. Tambets, I. Antanaitis-Jacobs, M.N. Haidle, R. Jankauskas, C.-J. Kind, F. Lueth, T. Terberger, J. Hiller, S. Matsumura, P. Forster, & J. Burger. (2009). Genetic discontinuity between local hunter-gatherers and Central Europe’s first farmers, Science, 326, 137-140
Malmström, H., M.T.P. Gilbert, M.G. Thomas, M. Brandström, J. Storå, P. Molnar, P.K. Andersen, C. Bendixen, G. Holmlund, A. Götherström, & E. Willerslev (2009). Ancient DNA Reveals Lack of Continuity between Neolithic Hunter-Gatherers and Contemporary Scandinavians, Current Biology, doi:10.1016/j.cub.2009.09.017
This argument raises one obvious problem. It implies that the physical characteristics of Europeans, especially northern Europeans, arose recently and over a short time.
How short? As late as 7500 years ago, hunter-fisher-gatherers still inhabited Europe above a line running from the Netherlands to the Black Sea. The line then gradually moved north, reaching northern Germany about 5500 BP and the eastern and northern agricultural areas of Scandinavia around 4300 BP. This leaves very little time for the evolution of the northern European phenotype, i.e., lightening of the skin to pinkish-white and diversification of hair and eye color into a wide range of hues. This phenotype is attested by historical records going back over two thousand years, so we’re left with a time window of less than five thousand years.
Is that enough time for so much phenotypic change? Perhaps, but the selection pressures would have to be very strong.
Let’s turn to the first of the two papers. Bramanti et al. (2009) compared mtDNA sequences from late hunter-gatherers and early farmers who had lived in northern and central Europe (Lithuania, Poland, Russia, Germany). There was no evidence of genetic continuity between the two populations.
But this paper raises several other points:
1. Modern Europeans are almost as distant genetically from the early farmers as they are from the late hunter-gatherers. To be ancestral to modern Europeans, these farmers and their descendents would need a very low female population size (less than 3,000 individuals). As the authors admit, this figure is well below current archaeological estimates (124,000 individuals).
2. The sample sizes are very small for the early farmers (25 individuals) and the late hunter-gatherers (20 individuals).
3. The sample of late hunter-gatherers covers a much longer time frame (15,400 – 4300 BP) than does the sample of early farmers (7650 - 7400 BP).
In sum, the authors have tried to describe the gene pool of late European hunter-gatherers with data from 20 individuals spread over four countries and over some 11,000 years.
Can such a sample be representative? Doubtful. Besides the smallness of the sample, the late hunter-gatherers were not a homogeneous population. By their time, Europe had completely changed ecologically. Open tundra had given way to forest and it was no longer possible to hunt wandering herds of reindeer. Hunter-gatherers now lived in smaller and more localized groups. Each group would have had its own genetic profile as a result of genetic drift and founder effects.
Even if these 20 individuals fairly represented late hunter-gatherers, the genetic continuity hypothesis is not disproved by genetic differences between them and early farmers. Undoubtedly, some hunter-gatherers adopted farming earlier than others and thus contributed more to the early farmer gene pool. Others never adopted farming and thus contributed nothing. Founder effects would have been considerable.
There are thus two serious problems with Bramanti et al. (2009):
1. The sample of late hunter-gatherers is too small and too scattered over space and time to be representative of the late hunter-gatherer gene pool;
2. The genetic continuity hypothesis does not assume that the early farmer gene pool was a representative cross-section of the late hunter-gatherer gene pool.
Let’s turn to the other paper. Malmström et al. (2009) retrieved mtDNA from 19 late hunter-gatherers and 3 early farmers who lived in southern Scandinavia. The late hunter-gatherers show no genetic continuity with the early farmers or with modern Scandinavians but they do show genetic continuity with modern Baltic populations (i.e., Latvians). This seems consistent with archaeological evidence that the eastern Baltic was a refugium for Europe’s last hunter-gatherers. Indeed, the inland boundaries of Latvia, Lithuania, and Old Prussia may hark back to a time when these people fished and sealed from coastal stations part of the year and then moved some distance inland to hunt game the rest of the year.
This study has the merit of being more narrowly focused in time and space. Like the other study, however, it suffers from very small sample sizes and the likelihood of founder effects. In fact, the early farmer sample is so small that genetic continuity with modern Scandinavians is unsure.
What now?
The challenge now will be to enlarge this sample of late hunter-gatherers. By ‘enlarge’, I don’t simply mean a larger sample. I also mean a larger number of geographic locations to be sampled. Late hunter-gatherers were a heterogeneous bunch. Some contributed a lot to the future gene pool. Others went extinct.
The ‘losers’ were small inland hunting bands with low population densities. They were less able to integrate agriculture into their nomadic way of life and also more likely to retreat in the face of much larger farming communities.
The ‘winners’ were semi-sedentary coastal groups with relatively high population densities. Because such groups depended more on fishing and sealing than on hunting and gathering, they could more readily integrate farming into their lifestyle, if only as a secondary subsistence activity. They were also more numerous and likelier to withstand encroachment by farming communities.
References
Bramanti, B., M.G. Thomas, W. Haak, M. Unterlaender, P. Jores, K. Tambets, I. Antanaitis-Jacobs, M.N. Haidle, R. Jankauskas, C.-J. Kind, F. Lueth, T. Terberger, J. Hiller, S. Matsumura, P. Forster, & J. Burger. (2009). Genetic discontinuity between local hunter-gatherers and Central Europe’s first farmers, Science, 326, 137-140
Malmström, H., M.T.P. Gilbert, M.G. Thomas, M. Brandström, J. Storå, P. Molnar, P.K. Andersen, C. Bendixen, G. Holmlund, A. Götherström, & E. Willerslev (2009). Ancient DNA Reveals Lack of Continuity between Neolithic Hunter-Gatherers and Contemporary Scandinavians, Current Biology, doi:10.1016/j.cub.2009.09.017
Thursday, October 22, 2009
Face and gender recognition
It is told that an elder came to Scete with his son who was not yet weaned. The boy was raised in the monastery and did not know there were women. When he became a man, the demons represented images of women to him. He was astonished and informed his father. Now one day the two of them went to Egypt and, seeing some women, the young man told his father, “Father, those are the ones who would come and see me at Scete during the night!”
Sayings of the Fathers (Apophthegmata Patrum) 5th century (Regnault, 1966, p.73)
We seem to be born with the ability to recognize the human face. Even infants as young as 1 month old show a consistent, spontaneous preference for face-like stimuli over nonface-like patterns. Such recognition seems guided by an inborn representation of the main facial features, particularly the eyes and the mouth (Pascalis & Kelly, 2008). Brain-damaged subjects provide further evidence of a mental module that specifically processes facial images:
Associative visual agnosia does not always seem to affect the recognition of all types of stimuli equally. The selectivity in some cases of agnosia lends support to the view that there are specialized systems for recognizing particular types of stimuli. The best known example of this is prosopagnosia, the inability to recognize faces after brain damage. Prosopagnosics cannot recognize familiar people by their faces alone, and must rely on other cues for recognition such as a person’s voice, or distinctive clothing or hairstyles. The disorder can be so severe that even close friends and family members will not be recognized. Although many prosopagnosics have some degree of difficulty recognizing objects other than faces, in some cases the deficit appears strikingly selective for faces. (Farah, 1996)
If this mental representation is inborn, does it come in two forms, one for a female face and another for a male face? Or is it gender-neutral? By studying visual adaptation to facial images, Little et al. (2005) concluded that different neural populations process male and female faces. This difference seems to exist at the level of higher-level neurons that code for the entire face, rather than for specific characteristics (Bestelmeyer et al., 2008). These findings were partially replicated by Jaquet (2007), who found evidence for both common and sex-selective neurons.
Ramsey-Rennels and Langlois (2006) reviewed the literature on male and female face recognition by infants:
First, 3- to 4-month-olds have more difficulty discriminating among male faces and subsequently recognizing them than they do female faces (Quinn et al., 2002). Second, older infants are more skilled at categorizing female faces than they are at categorizing male faces: Whereas 10-month-olds easily recognize that a sex-ambiguous female face does not belong with a group of sex-typical female faces, they have more difficulty excluding a sex-ambiguous male face from a group of sex-typical male faces (data interpretation of Younger & Fearing, 1999, by Ramsey et al., 2005). In addition, there is a lag between when infants recognize that female voices are associated with female faces and when male voices are associated with male faces; infants reliably match female faces and voices at 9 months (Poulin-Dubois, Serbin, Kenyon, & Derbyshire, 1994) but do not reliably match male faces and voices until 18 months. Even at 18 months, infants are more accurate at matching female faces and voices than they are at matching male faces and voices (Poulin-Dubois, Serbin, & Derbyshire, 1998).
This evidence could be interpreted in two ways: a) infants better recognize female faces because they have more experience with mothers than with fathers; or b) female face recognition develops earlier than male face recognition because humans have evolved to recognize a female caregiver at an early age. To date, there has been no attempt to replicate the above findings with mother-absent/father-present infants. Quinn et al. (2002) found that such infants show a weak preference for male faces (59%) but there is no indication that they are better at recognizing male faces than female ones.
References
Bestelmeyer, P.E.G., B.C. Jones, L.M. DeBruine, A.C. Little, D.I. Perrett, A. Schneider, L.L.M. Welling, & C.A. Conway. (2008). Sex-contingent face aftereffects depend on perceptual category rather than structural encoding, Cognition, 107, 353-365.
Duchaine, B.C., G. Yovel, E.J. Butterworth, & K. Nakayama. (2006). Prosopagnosia as an impairment to face-specific mechanisms: Elimination of the alternative hypotheses in a developmental case, Cognitive Neuropsychology,
Farah, M.J. (1996). Is face recognition ‘special’? Evidence from neuropsychology, Behavioural Brain Research, 76, 181-189.
Jaquet, E. (2007). Perceptual aftereffects reveal dissociable adaptive coding of faces of different races and sexes, PhD thesis, School of Psychology, University of Western Australia.
Little, A.C., L.M. DeBruine, & B.C. Jones. (2005). Sex-contingent face aftereffects suggest distinct neural populations code male and female faces, Proceedings of the Royal Society of London, Series B, 272, 2283-2287.
Pascalis, O., & D.J. Kelly. (2008). Face processing, in M. Haith & J. Benson (eds.) Encyclopedia of Infant and Early Childhood Development, pp. 471-478, Elsevier.
Quinn, P.C., Yahr, J., Kuhn, A., Slater, A.M., & Pascalis, O. (2002). Representation of the gender of human faces by infants: A preference for female. Perception, 31, 1109–1121.
Ramsey-Rennels, J.L., & J.H. Langlois. (2006). Infants’ differential processing of female and male faces, Current Directions in Psychological Science, 15, 59-62.
Regnault, D.L. (1966). Les sentences des pères du désert. Les Apophtegmes des pères. Sarthe: Abbaye Saint-Pierre de Solesmes.
Thursday, October 15, 2009
Sexual selection and ancestral Europeans
I have argued that sexual selection has varied within our species in both intensity and direction (men selecting women or women selecting men) (Frost, 2006; Frost, 2008). In particular, it seems to have varied along a north-south gradient with men being more strongly selected in the tropical zone and women in the temperate and arctic zones. Women appear to have been most strongly selected among humans inhabiting ‘continental steppe-tundra’. This kind of environment creates the highest ratio of females to males among individuals willing to mate—by making it too costly for men to provision additional wives and by greatly raising male mortality over female mortality through long hunting distances.
Today, tundra is generally limited to discontinuous patches of land: arctic islands and coastlines, alpine areas above the tree line, etc. Yet it is only when tundra covers large land areas that it can support large herds of migrating herbivores. Such herds can in turn support a relatively large human population, but at the cost of high male mortality—because the men have to cover long distances to seek out and follow the wandering herds.
As late as 10,000 years ago, continental steppe-tundra covered an extensive land mass, particularly in Eurasia. It was thus one of the main adaptive landscapes of modern humans during their evolution outside Africa. In particular, it might explain the unusual physical appearance of Europeans, i.e., their feminized face shape and their complex of highly visible color traits (diverse palette of hair and eye colors, depigmentation of skin color to pinkish-white).
At this point, people ask: “But why would this sexual selection play out only in ice-age Europe? What about northern Asia? There must have been lots of steppe-tundra there as well.”
There was, but it lay much further north than in Europe and was less hospitable to humans. It was all the more inhospitable because it stretched further into the heart of Eurasia and away from the warming and moistening influence of the Atlantic. Thus, the Asian steppe-tundra never supported as many humans as did the European steppe-tundra. Indeed, it seems to have been devoid of human life at the height of the last ice age (Goebel, 1999, pp. 218, 222-223).
On a map of ice-age Eurasia, the steppe-tundra belt would look like a large blotch covering the plains of northern and eastern Europe plus a narrower strip running farther north across Asia. By a geographic accident—a large mass of ice covering Scandinavia—it had been pushed much further south in Europe than elsewhere. This was where the steppe-tundra could support substantial and continuous human settlement.
When making this argument, I usually stress the word ‘continuous.’ But the word ‘substantial’ is probably more important. The larger the population, the greater the chance that interesting variants will appear through mutation:
References
Frost, P. (2008). Sexual selection and human geographic variation, Proceedings of the 2nd Annual Meeting of the NorthEastern Evolutionary Psychology Society, The Journal of Social, Evolutionary & Cultural Psychology 2 (supp.), 49-65, www.jsecjournal.com/NEEPSfrost.pdf
Frost, P. (2006). European hair and eye color - A case of frequency-dependent sexual selection? Evolution and Human Behavior, 27, 85-103.
Goebel, T. (1999). Pleistocene human colonization of Siberia and peopling of the Americas: An ecological approach. Evolutionary Anthropology, 8, 208‑227.
Simpson, G.G. (1953). The Major Features of Evolution, New York: Columbia University Press.
Today, tundra is generally limited to discontinuous patches of land: arctic islands and coastlines, alpine areas above the tree line, etc. Yet it is only when tundra covers large land areas that it can support large herds of migrating herbivores. Such herds can in turn support a relatively large human population, but at the cost of high male mortality—because the men have to cover long distances to seek out and follow the wandering herds.
As late as 10,000 years ago, continental steppe-tundra covered an extensive land mass, particularly in Eurasia. It was thus one of the main adaptive landscapes of modern humans during their evolution outside Africa. In particular, it might explain the unusual physical appearance of Europeans, i.e., their feminized face shape and their complex of highly visible color traits (diverse palette of hair and eye colors, depigmentation of skin color to pinkish-white).
At this point, people ask: “But why would this sexual selection play out only in ice-age Europe? What about northern Asia? There must have been lots of steppe-tundra there as well.”
There was, but it lay much further north than in Europe and was less hospitable to humans. It was all the more inhospitable because it stretched further into the heart of Eurasia and away from the warming and moistening influence of the Atlantic. Thus, the Asian steppe-tundra never supported as many humans as did the European steppe-tundra. Indeed, it seems to have been devoid of human life at the height of the last ice age (Goebel, 1999, pp. 218, 222-223).
On a map of ice-age Eurasia, the steppe-tundra belt would look like a large blotch covering the plains of northern and eastern Europe plus a narrower strip running farther north across Asia. By a geographic accident—a large mass of ice covering Scandinavia—it had been pushed much further south in Europe than elsewhere. This was where the steppe-tundra could support substantial and continuous human settlement.
When making this argument, I usually stress the word ‘continuous.’ But the word ‘substantial’ is probably more important. The larger the population, the greater the chance that interesting variants will appear through mutation:
Small populations have limited variability at any one time and low absolute incidence of mutation, and they may be subject to genetic drift. They are also likely to be narrowly localized and so more subject to rapid extinction by a regional catastrophe. … Other things being equal, the larger the population the more potential variability, at least, it is likely to have and the larger its absolute rate of mutation will be. (Simpson, 1953, p. 297)
References
Frost, P. (2008). Sexual selection and human geographic variation, Proceedings of the 2nd Annual Meeting of the NorthEastern Evolutionary Psychology Society, The Journal of Social, Evolutionary & Cultural Psychology 2 (supp.), 49-65, www.jsecjournal.com/NEEPSfrost.pdf
Frost, P. (2006). European hair and eye color - A case of frequency-dependent sexual selection? Evolution and Human Behavior, 27, 85-103.
Goebel, T. (1999). Pleistocene human colonization of Siberia and peopling of the Americas: An ecological approach. Evolutionary Anthropology, 8, 208‑227.
Simpson, G.G. (1953). The Major Features of Evolution, New York: Columbia University Press.
Labels:
East Asians,
Europeans,
monogamy,
polygyny,
sexual selection
Thursday, October 8, 2009
Facial skin color and sexual selection
The human mind seems to use facial color to determine whether a person is male or female. A man has a relatively dark facial color that contrasts poorly with his lip and eye color. Conversely, a woman has a relatively light facial color that contrasts sharply with her lip and eye color (Russell, 2003; Russell, 2009; Russell, in press).
This kind of sex-recognition algorithm has been a channel for sexual selection in many species. When selecting a mate, an animal tends to choose the ones most easily recognizable as the opposite sex. Over many generations, such selection will cause the relevant sex-specific cues to be accentuated (Manning, 1972, pp. 47-49).
The degree of accentuation will depend on the intensity of sexual selection and on whether males have been selecting females or females selecting males. Among ancestral humans, sexual selection seems to have varied in both intensity and direction along a north-south gradient (Frost, 2006; Frost, 2008). In the tropical zone, women gathered food year-round, so a second wife would cost little in terms of food provisioning. With more men becoming polygynous, fewer women were left unmated. The pressure of sexual selection was thus on men, with women being the ones who could pick and choose mates.
This situation reversed outside the tropical zone. First, polygyny was costlier because women could not gather food in winter. Second, male mortality exceeded female mortality because men had to hunt over longer distances. Together, these two trends resulted in too few men competing for too many women. This was particularly so on continental steppe-tundra, where women had almost no opportunities for food gathering and where men had to hunt wandering herds of herbivores over long distances. The pressure of sexual selection was thus on women, with men being the ones who could pick and choose mates.
Sexual selection and lightening of skin color
If light skin is perceived as a sign of femininity, sexual selection of women should tend to lighten female skin. This kind of selection became possible once ancestral humans had left the tropical zone. On the one hand, there was less natural selection for dark skin as a barrier to intense UV radiation. On the other, as explained above, there was stronger sexual selection of women because they outnumbered men on the mate market. Women should thus be increasingly lighter-skinned than men with increasing distance from the tropical zone, this sex difference being greatest among those humans that once inhabited the large expanses of continental steppe-tundra in northern and eastern Europe. Since most skin pigmentation genes are not sex-linked, selection for lighter-skinned women would also lighten mean skin color (i.e., both males and females). Thus, mean skin color should likewise lighten along the same north-south gradient.
How do these predictions stack up against reality? They accurately describe geographic variation in mean skin color (Frost, 2008). But they poorly describe geographic variation in female depigmentation relative to male skin color. In fact, female skin reflectance exceeds male skin reflectance the most among humans at medium latitudes with medium skin color (Frost, 2007; Madrigal & Kelly, 2006). This may be a ‘ceiling effect’. Northern and eastern Europeans are close to the physiological limit of skin depigmentation. Their women cannot be much whiter than the mean skin color because they have, so to speak, very little headroom left—the mean skin color is already scrunched up against the ceiling of maximum skin whiteness.
Sexual selection and increase in facial color contrast
There seems to be similar geographic variation in the contrast between facial color and lip/eye color. This contrast is weakest among tropical humans. It is strongest, however, not among northern/eastern Europeans but among East Asians (Russell, in press). This is largely because East Asians have dark eyes and relatively light facial skin. The contrast effect is even stronger if we factor in their jet-black hair, which further sets off the lightness of the female face. Nonetheless, facial color contrast is no more sexually dimorphic among East Asians than it is among Europeans (Russell, in press).
Why would Europeans score lower than East Asians on facial color contrast? It may be that sexual selection for dark eyes and dark hair relaxed among ancestral Europeans once their facial skin had lightened to the point of becoming pinkish-white. At that point, the color contrast was more than sufficient. This, in turn, may have allowed rare color preference to generate sexual selection for diverse hair and eye colors. This process may have then acquired a dynamic of its own that competed with the older dynamic of facial color contrast. Alternately, rare color preference may have always been a weak selection pressure that manifests itself only under conditions of intense sexual selection (Frost, 2006; Frost, 2008).
Conclusion
In sum, if we examine geographic variation in skin color and in facial color contrast, the pattern is largely consistent with increasingly intense sexual selection of women along a north-south gradient. This selection would have been minimal among tropical humans and maximal among arctic humans, particularly those that once lived on continental steppe-tundra—where polygyny was constrained the most and where male mortality exceeded female mortality the most. There are, however, deviations from the expected pattern that may be due to ceiling effects and release of sexual selection for rare hair and eye colors.
Among ancestral Europeans, this process of sexual selection seems to have been a multi-stage process. It likely began c. 30,000 BP with the first penetration by modern humans of the steppe-tundra belt (southwestern France). This initial stage would correspond to certain physical changes that are common to Europeans and East Asians. Stage I ended with the onset of the glacial maximum (c. 20,000 BP), which blocked East-West gene flow by merging the Fenno-Scandian and Ural icecaps and by forming large glacial lakes along the Ob (Rogers, 1986; Crawford et al, 1997). Stages II and III would correspond to later physical changes that are specific to Europeans.
Stage I – head hair lengthens, face shape feminizes, skin lightens (30,000–20,000 BP ?)
Stage II – skin lightens to pinkish-white (20,000–15,000 BP ?)
Stage III – hair and eye color diversifies (15,000–10,000 BP ?)
References
Crawford, M.H., Williams, J.T., & Duggirala, R. (1997). Genetic structure of the indigenous populations of Siberia. American Journal of Physical Anthropology, 104, 177-192.
Frost, P. (2008). Sexual selection and human geographic variation, Proceedings of the 2nd Annual Meeting of the NorthEastern Evolutionary Psychology Society, The Journal of Social, Evolutionary & Cultural Psychology 2 (supp.), 49-65, www.jsecjournal.com/NEEPSfrost.pdf
Frost, P. (2007). Comment on Human skin-color sexual dimorphism: A test of the sexual selection hypothesis, American Journal of Physical Anthropology, 133, 779-781.
Frost, P. (2006). European hair and eye color - A case of frequency-dependent sexual selection? Evolution and Human Behavior, 27, 85-103.
Madrigal, L., & W. Kelly. (2006). Human skin-color sexual dimorphism: A test of the sexual selection hypothesis, American Journal of Physical Anthropology, 132, 470-482.
Manning, A. (1972). An Introduction to Animal Behaviour, 2nd edition, London: Edward Arnold.
Rogers, R.A. (1986). Language, human subspeciation, and Ice Age barriers in Northern Siberia. Canadian Journal of Anthropology, 5, 11‑22.
Russell, R. (in press). Why cosmetics work. In Adams, R., Ambady, N., Nakayama, K., & Shimojo, S. (Eds.) The Science of Social Vision. New York: Oxford University Press.
Russell, R. (2009). A sex difference in facial contrast and its exaggeration by cosmetics, Perception, 38, 1211-1219.
Russell, R. (2003). Sex, beauty, and the relative luminance of facial features, Perception, 32, 1093-1107.
This kind of sex-recognition algorithm has been a channel for sexual selection in many species. When selecting a mate, an animal tends to choose the ones most easily recognizable as the opposite sex. Over many generations, such selection will cause the relevant sex-specific cues to be accentuated (Manning, 1972, pp. 47-49).
The degree of accentuation will depend on the intensity of sexual selection and on whether males have been selecting females or females selecting males. Among ancestral humans, sexual selection seems to have varied in both intensity and direction along a north-south gradient (Frost, 2006; Frost, 2008). In the tropical zone, women gathered food year-round, so a second wife would cost little in terms of food provisioning. With more men becoming polygynous, fewer women were left unmated. The pressure of sexual selection was thus on men, with women being the ones who could pick and choose mates.
This situation reversed outside the tropical zone. First, polygyny was costlier because women could not gather food in winter. Second, male mortality exceeded female mortality because men had to hunt over longer distances. Together, these two trends resulted in too few men competing for too many women. This was particularly so on continental steppe-tundra, where women had almost no opportunities for food gathering and where men had to hunt wandering herds of herbivores over long distances. The pressure of sexual selection was thus on women, with men being the ones who could pick and choose mates.
Sexual selection and lightening of skin color
If light skin is perceived as a sign of femininity, sexual selection of women should tend to lighten female skin. This kind of selection became possible once ancestral humans had left the tropical zone. On the one hand, there was less natural selection for dark skin as a barrier to intense UV radiation. On the other, as explained above, there was stronger sexual selection of women because they outnumbered men on the mate market. Women should thus be increasingly lighter-skinned than men with increasing distance from the tropical zone, this sex difference being greatest among those humans that once inhabited the large expanses of continental steppe-tundra in northern and eastern Europe. Since most skin pigmentation genes are not sex-linked, selection for lighter-skinned women would also lighten mean skin color (i.e., both males and females). Thus, mean skin color should likewise lighten along the same north-south gradient.
How do these predictions stack up against reality? They accurately describe geographic variation in mean skin color (Frost, 2008). But they poorly describe geographic variation in female depigmentation relative to male skin color. In fact, female skin reflectance exceeds male skin reflectance the most among humans at medium latitudes with medium skin color (Frost, 2007; Madrigal & Kelly, 2006). This may be a ‘ceiling effect’. Northern and eastern Europeans are close to the physiological limit of skin depigmentation. Their women cannot be much whiter than the mean skin color because they have, so to speak, very little headroom left—the mean skin color is already scrunched up against the ceiling of maximum skin whiteness.
Sexual selection and increase in facial color contrast
There seems to be similar geographic variation in the contrast between facial color and lip/eye color. This contrast is weakest among tropical humans. It is strongest, however, not among northern/eastern Europeans but among East Asians (Russell, in press). This is largely because East Asians have dark eyes and relatively light facial skin. The contrast effect is even stronger if we factor in their jet-black hair, which further sets off the lightness of the female face. Nonetheless, facial color contrast is no more sexually dimorphic among East Asians than it is among Europeans (Russell, in press).
Why would Europeans score lower than East Asians on facial color contrast? It may be that sexual selection for dark eyes and dark hair relaxed among ancestral Europeans once their facial skin had lightened to the point of becoming pinkish-white. At that point, the color contrast was more than sufficient. This, in turn, may have allowed rare color preference to generate sexual selection for diverse hair and eye colors. This process may have then acquired a dynamic of its own that competed with the older dynamic of facial color contrast. Alternately, rare color preference may have always been a weak selection pressure that manifests itself only under conditions of intense sexual selection (Frost, 2006; Frost, 2008).
Conclusion
In sum, if we examine geographic variation in skin color and in facial color contrast, the pattern is largely consistent with increasingly intense sexual selection of women along a north-south gradient. This selection would have been minimal among tropical humans and maximal among arctic humans, particularly those that once lived on continental steppe-tundra—where polygyny was constrained the most and where male mortality exceeded female mortality the most. There are, however, deviations from the expected pattern that may be due to ceiling effects and release of sexual selection for rare hair and eye colors.
Among ancestral Europeans, this process of sexual selection seems to have been a multi-stage process. It likely began c. 30,000 BP with the first penetration by modern humans of the steppe-tundra belt (southwestern France). This initial stage would correspond to certain physical changes that are common to Europeans and East Asians. Stage I ended with the onset of the glacial maximum (c. 20,000 BP), which blocked East-West gene flow by merging the Fenno-Scandian and Ural icecaps and by forming large glacial lakes along the Ob (Rogers, 1986; Crawford et al, 1997). Stages II and III would correspond to later physical changes that are specific to Europeans.
Stage I – head hair lengthens, face shape feminizes, skin lightens (30,000–20,000 BP ?)
Stage II – skin lightens to pinkish-white (20,000–15,000 BP ?)
Stage III – hair and eye color diversifies (15,000–10,000 BP ?)
References
Crawford, M.H., Williams, J.T., & Duggirala, R. (1997). Genetic structure of the indigenous populations of Siberia. American Journal of Physical Anthropology, 104, 177-192.
Frost, P. (2008). Sexual selection and human geographic variation, Proceedings of the 2nd Annual Meeting of the NorthEastern Evolutionary Psychology Society, The Journal of Social, Evolutionary & Cultural Psychology 2 (supp.), 49-65, www.jsecjournal.com/NEEPSfrost.pdf
Frost, P. (2007). Comment on Human skin-color sexual dimorphism: A test of the sexual selection hypothesis, American Journal of Physical Anthropology, 133, 779-781.
Frost, P. (2006). European hair and eye color - A case of frequency-dependent sexual selection? Evolution and Human Behavior, 27, 85-103.
Madrigal, L., & W. Kelly. (2006). Human skin-color sexual dimorphism: A test of the sexual selection hypothesis, American Journal of Physical Anthropology, 132, 470-482.
Manning, A. (1972). An Introduction to Animal Behaviour, 2nd edition, London: Edward Arnold.
Rogers, R.A. (1986). Language, human subspeciation, and Ice Age barriers in Northern Siberia. Canadian Journal of Anthropology, 5, 11‑22.
Russell, R. (in press). Why cosmetics work. In Adams, R., Ambady, N., Nakayama, K., & Shimojo, S. (Eds.) The Science of Social Vision. New York: Oxford University Press.
Russell, R. (2009). A sex difference in facial contrast and its exaggeration by cosmetics, Perception, 38, 1211-1219.
Russell, R. (2003). Sex, beauty, and the relative luminance of facial features, Perception, 32, 1093-1107.
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