French Canadians: an evolving gene pool

In French Canadians, Tay Sach’s is caused by 2 different mutations that arose within a relatively small geographic area and short time frame (neither mutation is reported in France). This area (Bas St-Laurent and Charlevoix) is also the one where English Canadian merchants and managers were historically the least present. Is there a link between the two?

The field of human genetics has focused more on some gene pools than on others, with French Canadians being one of its favorites. There are two reasons:

1. While numbering some six million today in Quebec alone, they descend almost entirely from 8,500 or so founders—mostly French settlers with some Amerindian and British admixture. Such a homogeneous gene pool can more easily show how mutations spread and how natural selection works.

2. The genetic lineages are relatively easy to reconstruct for the past three to four centuries, partly because French Canadians have tended to stay put in the same locality, at least until recently, and partly because Catholic parishes have kept detailed records of births, marriages, and deaths.

The French Canadian gene pool is showing us that human evolution did not stop in remote prehistoric times. Yes, natural selection is ongoing. It has produced significant genetic change even over the last three to four centuries.

Decline in Amerindian admixture

One example of recent selection is the decline in Amerindian admixture. According to a genealogical study of parish registers, Amerindians made up 1.2% of all founders but now account for only 0.1 - 0.3% of current ancestry (Bherer et al., 2010).

Both estimates certainly understate Amerindian admixture. Such admixture was under-reported by parish registers because it tended to occur in frontier areas and through common-law marriages. Amerindian admixture also entered the French Canadian gene pool via Acadians, whom Bherer et al (2010) list as a separate ethnic group.

Nonetheless, this under-reporting should have affected the above two estimates more or less equally. If we look at the lineages for which we do have information, it seems that Amerindian admixture has tended to reduce their reproductive success.

Why? One reason is that it largely occurred among French settlers who were already more marginal than average, either socially (lower on the social scale) or spatially (farther away from the main zone of settlement). Such people had fewer opportunities for success and thus tended to have fewer children who would survive to adulthood.

Ferron and Cliché (1982, p. 35) describe this social differentiation for Beauce County, in southeastern Quebec:

Beginning in the 19th century, the inhabitants were split into two social groups. In one, the inhabitants were stable, hardworking, preoccupied with their heritage of land and family, and governed by an increasingly strict ethic. In the other group were the marginal folk, the métissés [mixed with Amerindians], the less rich, and those who mucked about. They would settle on the periphery of the parish, in “the concessions” …

Because the two groups differed in their circumstances, behavior, and sub-cultural characteristics, it is hardly surprising that they followed different trajectories of reproductive success.

Tay Sach’s: founder effect or selection?

Tay Sach’s disease is unusually common among French Canadians, particularly in eastern Quebec. In Rimouski, the heterozygote frequency is 7.6%, compared to 4.2% for Ashkenazi Jews and 0.3% for French Canadians in Montreal (De Braekeleer et al, 1992). The medical literature almost always explains it as a founder effect that was amplified by the rapid population growth of French Canadians from the mid-18th to mid-20th centuries.

This explanation is challenged by Zlotogora (1994), who points out that French Canadian Tay Sach’s is produced by two different mutations: one that originated on the south shore of the lower St. Lawrence and another that originated on the north shore (Charlevoix County). Neither mutation has been reported from France. Thus, on two separate occasions and in a very small population, something has maintained a genetic mutation that has failed to maintain itself in a much larger population.

Nor does a founder effect easily explain how 2 out of 8,500 founders (0.02%) could have produced the incidences we now see in eastern Quebec or even French Canada in general.

In Ashkenazi Jews, the high incidence of Tay Sach’s has been attributed to natural selection, specifically some advantage associated with mental processing. Indeed, Tay Sach’s is one of four different genetic illnesses that are unusually common among Ashkenazim and that affect the same metabolic pathway in brain tissues (lysosomal storage) (Zlotogora, 1994). In the homozygous state, the alleles in question produce neurological degeneration, mental retardation, and other neural problems. In the heterozygous state, however, they may have helped Ashkenazi Jews cope with mentally demanding occupations, such as in finance or in cottage industry crafts (Cochran et al., 2006; Frost 2007; Murray, 2007)

But why would this natural selection operate among French Canadians? Weren’t they the ones who toiled on the land and in the factories while English Canadians monopolized the skilled brainwork of trade, accounting, and management? First of all, this is a caricature of reality. There has always been a French Canadian middle class, although it was historically smaller in size than the English Canadian one.

More to the point, middle-class English Canadians were not uniformly spread across the province. Demographically and economically, they used to dominate the Ottawa valley, the Montreal area, the Eastern Townships, Quebec City, and the eastern and southern portions of the Gaspé Peninsula. Economically, they also dominated the hinterland of Trois-Rivières and the Lac Saint-Jean region (timber industry). This leaves two regions where, historically, they were virtually non-existent—the same regions that report unusually high incidences of Tay Sach’s.

An economic niche existed and had to be filled. In the absence of ethnic outsiders, middle-class French Canadians would have had more opportunities to go into business, marry earlier, and have larger families. Is this what happened in the lower St. Lawrence and Charlevoix County?

An obvious test would be to review Tay Sach genealogies in these two regions to see whether heterozygotes were over-represented in mentally demanding occupations, i.e., small business, law, medicine, accounting, etc.

References

Bherer, C., D. Labuda, M.-H. Roy-Gagnon, L. Houde, M. Tremblay, and H. Vézina (2010). Admixed ancestry and stratification of Quebec regional populations, American Journal of Physical Anthropology, in press.

Cochran, G., J. Hardy, & H. Harpending. (2006). Natural history of Ashkenazi intelligence. Journal of Biosocial Science, 38, 659-693.

De Braekeleer, M., P. Hechtman, E. Andermann, and F. Kaplan. (1992). The French Canadian Tay-Sachs disease deletion mutation: identification of probable founders, Human Genetics, 89, 83-87.

Ferron, M. & R. Cliché. (1982). Les Beaucerons. Ces insoumis, Montreal: Hurtubise HMH.

Frost, P. (2007). Natural selection in proto-industrial Europe, Evo and Proud, November 16.
http://evoandproud.blogspot.com/2007/11/natural-selection-in-proto-industrial.html

Murray, C. (2007). Jewish Genius. Commentary, April

Roy-Gagnon, M-H., C. Moreau, C. Bherer, P. St-Onge, D. Sinnett, C. Laprise, H. Vézina, D. Labuda. (2011). Genomic and genealogical investigation of the French Canadian founder population structure, Human Genetics, in press.

Zlotogora, J. (1994). High frequencies of human genetic diseases: founder effect with genetic drift or selection? American Journal of Medical Genetics, 49, 10-13.

Religiosity and the origins of civilization

Scenes of daily life from Sumer. The causes of civilization are not to be found in early art, writing, or architecture. These are merely the consequences of a preceding mental revolution.

Humans have gone through three stages of development: hunting/gathering, simple agricultural societies, and complex agricultural societies. The last stage brought us most of what we call “civilization”— state formation, class differentiation, urbanization, writing systems, literate culture, and so on.

What caused this transition from simple to complex agricultural societies? Was it simply the passage of time? Doubtful. Some societies have made this transition sooner than others. Others have never made it.

According to Atkinson and Whitehouse (2011), this debate has shifted away from technological causes and toward social and symbolic ones:

The main drivers of the great transition from small-scale hunter-gatherer societies in the pre-pottery Neolithic to the vast and complex civilizations of East Asia, MesoAmerica and the Fertile Crescent are still much debated […] Doubts have been growing with respect to the explanatory power of technological innovation, and attention has been focused increasingly on changes in social and symbolic worlds.

For the two authors, the change in the mode of subsistence (from hunting/gathering to agriculture) paved the way for a change in the mode of religiosity. It was this second transition that actually made the complexification of society possible. Humans became accustomed to a more systematized and accumulative form of thinking, and it was this new mental space that eventually became translated into a new physical space of buildings, roads, towns, and so forth.

Atkinson and Whitehouse argue that human societies seem to cluster into two modes of religiosity:

1. An “imagistic” mode associated with hunter-gatherers. Religiosity is focused on non-routine events that evoke an intense state of mental arousal (initiation, ordeals, bodily mutilation, etc).

2. A “doctrinal” mode associated with agricultural societies. Religiosity is more routine and is focused on frequently repeated teachings and rituals that generally evoke a less intense state of mental arousal.

Among hunter-gatherers, religiosity is meant to be traumatic. The aim is to create a vivid experience with long-lasting effects, such as an emotional bond that will keep men loyal to each other for hunting or war.

In agricultural societies, religiosity supports tasks that occur more often and more regularly:

Whereas the exploitation of wild resources requires only sporadic group co-operation (e.g., in hunting larger game), the domestication of animals and plants fosters increasingly routinized forms of collaborative labour (e.g., clearing, planting, harvesting and building). In traditional societies, such activities are typically punctuated by rituals.

There is thus selection for a new kind of mental space:

Put simply, the proposed doctrinal mode is seen as favouring high-frequency, low-arousal rituals, allowing large bodies of religious teachings to be stored in semantic memory, reproduced stably and spread efficiently as oral tradition.

[…] The doctrinal mode is based around frequently repeated teachings and rituals. High-frequency ritual performances allow complex networks of ideas to be transmitted and stored in semantic memory and give rise to generic identity markers ascribed to large-scale ‘imagined communities.’

It was this new mental space that made complex societies possible. Thus, the causes of civilization are not to be found in early art, writing, or architecture. These are merely the consequences of a preceding mental revolution. Atkinson and Whitehouse argue that the doctrinal mode of religiosity created a positive feedback loop of increasing cultural complexity:

If the emergence of agriculture drives an overall increase in the frequency of communal rituals, it also indirectly opens up opportunities for other features of the doctrinal mode to appear.

Other features might include organized priesthoods, ways to codify, transmit, and organize religious traditions (such as writing), and methods to enforce group cooperation and resource control.

Atkinson and Whitehouse do not ask why this mental revolution occurred in some agricultural societies and not in others. Tropical horticulturalists, for example, seem to have permanently stalled at the stage of simple societies. One reason may be that year-round agriculture enables women to provide for themselves and their offspring with limited male assistance. When agriculture is largely a female task, it is less likely to generate communal forms of religiosity that structure everyone’s mental space.

In addition, female reproductive autonomy reduces the costs of polygyny and thus increases male-male rivalry for mates. Such rivalry makes it harder to bring the men of a community together into stable communal structures. Yet such structures must be in place before rituals can become fully communalized on a regular basis, this being the first step toward complexification of mental space and, hence, society itself.

Reference

Atkinson, Q.D. & H. Whitehouse. (2011). The cultural morphospace of ritual form : Examining modes of religiosity cross-culturally, Evolution & Human Behavior, 32, 50-62.

On Neanderthals, Denisovans, and other archaics

Andaman Islanders. Related peoples once inhabited the coastal regions of southern, southeastern, and eastern Asia.

The past year brought two major advances: the long awaited sequencing of the Neanderthal genome and the genetic sequencing of an another archaic human, the Denisovans of East Asia, whose existence had previously been unsuspected.

The bottom line comes down to four points:

Before the East African ‘big bang’ gave rise to modern humans some 80,000 to 60,000 years ago, there had been at least four groups of archaic humans:

a) Skhul-Qafzeh hominins
- were almost modern anatomically
- were derived from a demic expansion that spread over most of Africa and the Middle East about 110,000 years ago
- evolved directly into modern humans through the rapid expansion of an East African subgroup

b) Neanderthals
- differed much more anatomically from modern humans
- were behaviorally similar to Skhul-Qafzeh hominins
- probably had body fur and other cold adaptations
- were derived from an earlier expansion out of Africa 250,000 - 400,000 years ago
- inhabited Europe, the Middle East (during glacial maxima), Central Asia, and Siberia as far east as Lake Baikal

c) Hobbits
- were small and possibly a form of Homo erectus
- inhabited at least a portion of southeast Asia
- may have been a regional variant of the Denisovans

d) Denisovans (Homo altaiensis?)
- were another archaic population distinct from modern humans
- inhabited Asia from Lake Baikal eastward (see earlier post)

These archaic humans have left significant genetic admixture in all modern human populations. The admixture is about 1 to 4% in Eurasians (from Neanderthals), 8% in Melanesians (from Neanderthals and Denisovans), and 13% in sub-Saharan Africans (from Skhul-Qafzeh-like hominins).

This admixture might have accelerated human evolution by providing modern humans with useful alleles. To date, no such alleles have been found. The admixture seems to be confined to genes of low adaptive value.

Although Denisovans inhabited East Asia, they left no admixture in present-day East Asians. Yet their admixture is discernible in present-day Melanesians. It seems that the first modern humans to replace Denisovans were not ancestral East Asians but rather ancestral Melanesians. This is consistent with archeological and ethnographic evidence that the coastal regions of southern, southeastern, and eastern Asia were initially settled by people related to the indigenous populations of Melanesia, Papua-New Guinea, and Australia. After the last ice age, they were gradually replaced by populations originating in northern Eurasia (see earlier post). Today, they survive in relic groups like the Veddas of Sri Lanka, the Andaman Islanders, the Semang of the Malayan peninsula, and the Aeta of the Philippines.

References

Green, R.E., J. Krause, A.W. Briggs, T. Maricic, U. Stenzel, M. Kircher, et al. (2010). A draft sequence of the Neandertal genome, Science, 328, 710-722.
http://www.sciencemag.org/cgi/reprint/328/5979/710.pdf

Reich, D., R.E. Green, M. Kircher, J. Krause, N. Patterson, E.Y. Durand, et al. (2010). Genetic history of an archaic hominin group from Denisova Cave in Siberia." Nature, 468, 1053-1060.

Watson, E., P. Forster, M. Richards, and H-J. Bandelt. (1997). Mitochondrial footprints of human expansions in Africa, American Journal of Human Genetics, 61, 691-704.

Looking forward to 2011

Time to die. This parasitic fungus begins as a spore on an ant’s body. It germinates, grows inside its host and eventually directs the ant’s brain to climb a plant and clamp its mandibles around a leaf or stem. The fungus then kills its host.

It won’t be such a bad year. Stock markets will reach record highs and pundits will say we’ve entered a sustained boom. For many people, life will never again be so good as it will be this year.

The main worry will be price rises for many commodities. With a return to even modest rates of economic growth, demand will outstrip supply in several areas. Talk of “peak oil” will be joined by concerns over “peak food” and “peak water.” Serious water shortages will hit the American southwest and southeast.

There will also be concern over the decline in physical infrastructure, i.e., roads, bridges, and the like. Most of this infrastructure was built during the postwar boom of the 1950s and 1960s. Now it’s falling apart.

Finally, there will be concern over behavioral infrastructure, albeit less openly expressed. The market economy may be self-generating, but it doesn’t self-generate in a vacuum. As the historical economist Gregory Clark has shown, the market economy began to develop once a certain behavioral profile had become the norm—above all, a commitment to honesty and a rejection of violence and theft as means of self-enrichment. If the current population is replaced by one where people casually cheat and steal, transaction costs will escalate throughout the economy. A lot of economic activity will simply cease to be cost-effective.

Economists are afraid that a sharp rise in interest rates will abort the present recovery. Or a sharp rise in commodity prices. Frankly, I’m more worried about the behavioral changes.

Yes, humans are ingenious creatures. We’ll undoubtedly think of something. Nonetheless, the coming decade will confront us with several different challenges. Do we have enough fingers to plug all the holes in the dike? I’m not so sure, especially given the obliviousness of our political and economic elites.

Anyway, these problems won’t really bite until the second half of the decade. So enjoy life.

This year, I’ll try to use my recent book, Femmes claires, hommes foncés. Les racines oubliées du colorisme, to raise awareness of skin tone and gender/face recognition.

In short, the human face is a special visual object. We don’t learn to recognize it. Instead, the brain has a hardwired capacity for face recognition. This point is no longer debated. Controversy begins when we turn to the elements of this hardwired facial schema.

It is increasingly apparent, especially with recent work by Richard Russell and by Frédéric Gosselin’s research team, that one key element is skin tone, specifically facial coloration and luminosity. This visual element is apparently used to distinguish between male and female faces.

In pursuing this line of research, we should above all:

- locate the region of the brain that harbors this mental module. Gosselin’s team suggest that the location may be in the infero-temporal cortex, which handles both face perception and color perception. The best approach would likely be a real-time MRI study.

- show that this mental capacity is indeed hardwired and not learned. The best approach would be a twin study, such as Zhu et al (2009) used to show that face recognition is hardwired.

- identify other areas of cognition and behavior (sexual attraction, emotional distancing, etc.) that may be influenced by the output of this module.

The challenge here is not so much funding as access to special resources (real-time MRI brain scanning, large pools of identical and fraternal twins, etc.). And beyond that challenge lies another one: persuading other academics that this line of research is worth pursuing.

Other topics

This year, I hope to write posts on the following two topics. Depending on what turns up, these posts may eventually become publishable articles.

Parasite manipulation: Certain parasites can manipulate host behavior in a number of surprisingly specific ways. Although parasite manipulation has been documented for many non-human species, possible human examples are still lacking. One problem is paradigmatic. When a non-human animal acts strangely, we suspect parasite manipulation. When a human acts strangely, we just see a strange behavior.

I will argue that a likely candidate for parasite manipulation in our species is vaginal yeast, specifically the more aggressive strains associated with vulvovaginal candidiasis. This parasite has evolved the capacity to cross the blood/brain barrier and may manipulate certain neural circuits in both the female host and her regular male partner.

A new cold war? When the Cold War ended some two decades ago, it seemed that we had come to the “end of history.” All nations now agreed on the best social system: a free market economy combined with certain communitarian values (the family, the local community, the nation, etc.).

Yet, after a period of apparent convergence, the world is once more repolarizing into two opposing blocs. In the Eastern bloc, the decline of Marxism-Leninism has allowed a resurgence of pre-revolutionary social values, often with the encouragement of the State. Meanwhile, these same values are withering away in the Western bloc. Our ideal is now the self-defining individual who freely operates within a post-national, post-gender, and post-family world. But this freedom does not include the right to adhere to older social values. Such adherence is increasingly scorned as pathological, if not criminal.

This repolarization is especially visible on the Korean peninsula, where it is fueling renewed tensions. Will we see a Second Korean War? And will this war escalate into a larger, more global conflict?

References

Brainwashed by a parasite, Neurophilosophy, August 9, 2007
http://scienceblogs.com/neurophilosophy/2007/08/brainwashed_by_a_parasite.php

Clark, G.. (2007). A Farewell to Alms. A Brief Economic History of the World, Princeton University Press, Princeton and Oxford.

Clark, G. (2009). The indicted and the wealthy: surnames, reproductive success, genetic selection and social class in pre-industrial England,
http://www.econ.ucdavis.edu/faculty/gclark/Farewell%20to%20Alms/Clark%20-Surnames.pdf

Dupuis-Roy, N., I. Fortin, D. Fiset, and F. Gosselin. (2009). Uncovering gender discrimination cues in a realistic setting. Journal of Vision, 9(2), 10, 1–8.
http://journalofvision.org/9/2/10/, doi:10.1167/9.2.10.

Frost, P. (2010). Femmes claires, hommes foncés. Les racines oubliées du colorisme, Quebec City: Presses de l’Université Laval.

Russell, R. (2003). Sex, beauty, and the relative luminance of facial features, Perception 32: 1093-1107.

Russell, R., B. Duchaine, and K. Nakayama. (2009). Super-recognizers: People with extraordinary face recognition ability. Psychonomic Bulletin & Review, 16(2):252-257.

Russell, R. and P. Sinha. (2007). Real-world face recognition: The importance of surface reflectance properties, Perception 36: 1368-1374.

Russell, R., P. Sinha, I. Biederman, and M. Nederhouser. (2006). Is pigmentation important for face recognition? Evidence from contrast negation, Perception 35: 749-759.

Zhu, Q., Y. Song, S. Hu, X. Li, M. Tian, Z. Zhen, Q. Dong, N. Kanwisher, and J. Liu. (2009). Heritability of the specific cognitive ability of face perception, Current Biology, 20:137-142.

Review of 2010

Drinking from the wrong chalice? By his mid-40s, Michael Jackson had skin like parchment.

The end of 2010 is drawing nigh, and the time has come to review my predictions from last year.

Brain growth genes

Back in 2005, it was found that human populations vary considerably at two genes, ASPM and microcephalin, that control the growth of brain tissue. The finding seemed to be ‘huge’ in its implications. Then, it all fizzled out. No correlation could be found between variation at either gene and differences in mental ability or head circumference (Mekel-Bobrov et al., 2007; Rushton et al., 2007).

A recent study has now shown that ASPM and several other genes (MCPH1, CDK5RAP2, CENPJ) do in fact influence growth of brain tissue, specifically cortical tissue.

… In 2010, we’ll probably see further developments in this area. Stay tuned.

This year did see further developments. Interestingly, these gene loci seem to interact with sex and ethnicity in their effects:

[In a Norwegian study by Rimol et al.] for each of the 15 positive SNPs, the association was sex-specific with all significant results for CDK5RAP2 SNPs being found only in males, whilst the significant results for MCPH1 and ASPM were only found in females.

The second study, by Wang et al., only considered variation in the coding sequence of MCPH1 but found that one non-synonymous SNP is associated with male cranial volume but not female cranial volume in a Chinese population of nearly 900 individuals, supporting a role for sex in the action of microcephaly genes. Intriguingly, it also suggests that SNPs in the same locus can have opposite effects in males and females, as for MCPH1 an exonic SNP contributes to Chinese male cranial volume whilst intronic SNPs and SNPs downstream of the coding sequence are associated with Norwegian female brain size. As the authors discuss, these results strongly suggest some microcephaly variants may influence brain development dependent on hormonal background or through interactions with genes which are differentially expressed between the sexes, potentially contributing to sex specific differences in brain structure. (Montgomery & Mundy 2010)

But why did earlier studies find nothing?

First, many of the previous studies only tested for associations with the few, recently derived ASPM and MCPH1 haplotypes which were the focus of claims of recent positive selection, while both Rimol et al. and Wang et al. consider a larger number of SNPs for which there is no a priori evidence for selection. Second, despite the possibility of deriving clear hypotheses of what phenotypes these loci should affect, many previous studies examined traits that are, at best, not directly relevant (e.g. IQ or altruism) or quite distantly removed (e.g. adult head circumference). (Montgomery & Mundy 2010)

Many people had thought that all variation in mental capacity shows up on IQ tests. So they threw in the towel once it became apparent that IQ does not vary with genetic variation at these loci.

So how do these loci affect mental capacity? I’ve argued that the most recent ASPM variant seems to be associated with the spread of alphabetical writing. It may thus assist the visual cortex in recognizing, storing, and processing strings of alphabetical script (Frost 2008).

Alternatively, Dediu and Ladd (2007) have argued that ASPM and microcephalin variants correlate with use or non-use of tone languages. This hypothesis has been tested with Chinese, Korean, Hmong, and American Caucasians who had little training in tone recognition, i.e., they were not musicians and did not engage in singing or instrument playing. The Chinese and Koreans consistently outperformed the other participants when asked to identify the relative distance between two tones. The Hmong showed no such advantage, even though they shared the ASPM and microcephalin characteristics of the Chinese and Koreans (Hove et al., 2010). Thus, while some East Asian populations apparently are better at processing differences in pitch, this aptitude seems to be unrelated to ASPM or microcephalin.

Early modern human genome

Scientists have retrieved mtDNA from a 30,000 year-old hunter-gatherer from Kostenki, Russia. This seems to be part of a trend to study the genome of early modern humans.

The Kostenki mtDNA genome was entirely sequenced, despite problems that seemed intractable (difficulties in distinguishing between early modern human DNA and contamination from present-day human DNA). The authors concluded: “With this approach, it may even become possible to analyze the nuclear genomes of early modern humans” (Krause et al., 2010).

This development is indeed promising. If we can compare early modern DNA with present-day nuclear DNA, we’ll find out the exact genetic changes, especially those in neural wiring, that led to the ‘big bang’ of modern human evolution some 80,000 to 60,000 years ago. Unfortunately, this ‘big bang’ almost certainly took place in Africa, where the climate is much less conducive to DNA preservation.

Ethnic differences in vitamin D metabolism

This year will see further evidence that natural selection has caused differences in metabolism among different human populations, including vitamin D metabolism.

For instance, many populations have long been established at latitudes where vitamin-D synthesis is impossible for most of the year. Some of these populations can get vitamin D from dietary sources (e.g., fatty fish) but most cannot. In these circumstances, natural selection seems to have adjusted their metabolism to reduce their vitamin-D requirements. We know that the Inuit have compensated for lower production of vitamin D by converting more of this vitamin to its most active form (Rejnmark et al., 2004). They also seem to absorb calcium more efficiently, perhaps because of a different vitamin-D receptor genotype (Sellers et al., 2003). Even outside the Arctic zone, there seem to be differences in vitamin-D metabolism from one population to another. In particular, vitamin-D levels seem to be generally lower in darker-skinned populations (Frost, 2009).

… Unfortunately, our norms for adequate vitamin intake are based on subjects or populations of European origin. We are thus diagnosing vitamin-D deficiency in non-European individuals who are, in fact, perfectly normal. This is particularly true for African Americans, nearly half of whom are classified as vitamin-D deficient, even though few show signs of calcium deficiency—which would be a logical outcome. Indeed, this population has less osteoporosis, fewer fractures, and a higher bone mineral density than do Euro-Americans, who generally produce and ingest more vitamin D (Frost, 2009).

… What will be the outcome of raising vitamin-D levels in these populations? Keep in mind that we are really talking about a hormone, not a vitamin. This hormone interacts with the chromosomes and gradually shortens their telomeres if concentrations are either too low or too high. Tuohimaa (2009) argues that optimal levels may lie in the range of 40-60 nmol/L. In non-European populations the range is probably lower. It may also be narrower in those of tropical origin, since their bodies have not adapted to the wide seasonal variation of non-tropical humans.

If this optimal range is continually exceeded, the long-term effects may look like those of aging …

I hope that people of African or Native origin will resist the vitamin-D siren song. Otherwise, many of them will become shriveled-up husks by their mid-40s … just like Michael Jackson.

Evidence continued to mount this year that vitamin-D metabolism differs by ethnicity. For risk of atherosclerosis, the optimal range is lower among African Americans than among European Americans. A sample of African Americans showed a positive correlation between calcified plaque formation and blood levels of vitamin D (25(OH)D), despite a negative correlation among European Americans over the same range (Freedman et al., 2010).

Another study of African Americans found that blood levels of 25(OH)D decreased linearly with increasing African ancestry, the decrease being 2.5-2.75 nmol/L per 10% increase in African ancestry. Sunlight and diet were 46% less effective in raising these levels among subjects with high African ancestry than among those with low/medium African ancestry (Signorello et al. 2010).

The New York Times has recently covered the growing unease with vitamin D supplements:

The very high levels of vitamin D that are often recommended by doctors and testing laboratories — and can be achieved only by taking supplements — are unnecessary and could be harmful, an expert committee says.

… The 14-member expert committee was convened by the Institute of Medicine, an independent nonprofit scientific body, at the request of the United States and Canadian governments. It was asked to examine the available data — nearly 1,000 publications — to determine how much vitamin D and calcium people were getting, how much was needed for optimal health and how much was too much.

… Some labs have started reporting levels of less than 30 nanograms of vitamin D per milliliter of blood as a deficiency. With that as a standard, 80 percent of the population would be deemed deficient of vitamin D, Dr. Rosen said. Most people need to take supplements to reach levels above 30 nanograms per milliliter, he added.

But, the committee concluded, a level of 20 to 30 nanograms [50 to 75 nmol/L] is all that is needed for bone health, and nearly everyone is in that range.

… It is not clear how or why the claims for high vitamin D levels started, medical experts say. First there were two studies, which turned out to be incorrect, that said people needed 30 nanograms of vitamin D per milliliter of blood, the upper end of what the committee says is a normal range. They were followed by articles and claims and books saying much higher levels — 40 to 50 nanograms or even higher — were needed.

After reviewing the data, the committee concluded that the evidence for the benefits of high levels of vitamin D was “inconsistent and/or conflicting and did not demonstrate causality.”

Evidence also suggests that high levels of vitamin D can increase the risks for fractures and the overall death rate and can raise the risk for other diseases. (Kolata 2010)

H/T to Tod

References

Dediu, D., and D.R. Ladd (2007). Linguistic tone is related to the population frequency of the adaptive haplogroups of two brain size genes, ASPM and Microcephalin. Proceedings of the National Academy of Sciences, 104, 10944-10949.

Freedman B.I., L.E. Wagenknecht, K.G. Hairston KG et al. (2010). Vitamin D, adiposity, and calcified atherosclerotic plaque in African-Americans. Journal of Clinical Endocrinology & Metabolism, 95, 1076-1083.

Frost, P. (2009). Black-White differences in cancer risk and the vitamin-D hypothesis, Journal of the National Medical Association, 101, 1310-1313.

Frost, P. (2008). The spread of alphabetical writing may have favored the latest variant of the ASPM gene, Medical Hypotheses, 70, 17-20.

Hove, M.J., M.E. Sutherland, and C.L. Krumhansl. (2010). Ethnicity effects in relative pitch, Psychonomic Bulletin & Review, 17, 310-316.

Kolata, G. (2010). Report Questions Need for 2 Diet Supplements, The New York Times, November 29, 2010
http://www.nytimes.com/2010/11/30/health/30vitamin.html?_r=2&hp

Krause, J., A.W. Briggs, M. Kircher, T. Maricic, N. Zwyns, A. Derevianko, and S. Pääbo. (2010). A Complete mtDNA genome of an early modern human from Kostenki, Russia, Current Biology 20, 231–236.

Mekel-Bobrov, N., Posthuma D., Gilbert S.L., et al. (2007). The ongoing adaptive evolution of ASPM and Microcephalin is not explained by increased intelligence. Hum Mole Genet, 16, 600–8.

Montgomery, S.H. and N.I. Mundy. (2010). Brain Evolution : Microcephaly genes weigh in, Current Biology, 20(5), R244

Rejnmark L, Jørgensen ME, Pedersen MB, et al. (2004). Vitamin D insufficiency in Greenlanders on a Westernized fare: ethnic differences in calcitropic hormones between Greenlanders and Danes, Calcif Tissue Int, 74, 255-263.

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Gender/face recognition: hue and luminosity

Averaged female face (left) and averaged male face (right). The key facial regions for gender recognition, in terms of either response time or accuracy, seem to be where facial skin borders the lips or the eyes.

The human face is a special visual object. We do not learn to recognize it. Instead, it is processed by the brain via a hardwired mechanism. There seems to be an evolutionary tendency to hardwire recognition of objects that appear often enough while being significant enough to human existence.

One task of this mechanism is to tell a female face from a male face. To this end, we unconsciously focus on several visual cues, including skin tone. It is well established that skin pigmentation visibly differs between men and women. This sexual dimorphism reflects differences in both constitutive pigmentation (untanned skin) and facultative pigmentation (tanning capacity). In comparison to women, men have higher concentrations of melanin and hemoglobin in their skin and lower concentrations of carotene. Men also tan more readily than women do for equal exposure times.

The psychologist Richard Russell argues that this visual cue has two components: (1) the absolute luminosity of facial skin and (2) the contrast between this luminosity and that of the lips and the eyes. Now a study from the Université de Montréal points to a third component: differences in hue, i.e., the degree of ruddiness and yellowness. Hue assists gender recognition particularly where facial skin borders the mouth region. In contrast, luminosity is most helpful where facial skin borders the eye/eyebrow region.

This gender recognition works faster with hue than with luminosity. If the observer is too distant or the lighting too dim, the brain falls back on the “slow channel” of luminosity:

This suggests that humans do use chromatic cues for discriminating face gender: When it’s informative, they use it and respond rapidly (for evidence that color is perceived faster than shape, see Holcombe & Cavanagh, 2001; Moutoussis & Zeki, 1997a, 1997b); when it’s not, they have to rely on the more robust and more sluggish luminance cues.
(Dupuis-Roy et al., 2009)

Interestingly, the authors conclude that this mechanism may be located in the infero-temporal cortex, since this brain region is involved in both face perception and color perception.

H/T to Eugene

References

Dupuis-Roy, N., I. Fortin, D. Fiset, and F. Gosselin. (2009). Uncovering gender discrimination cues in a realistic setting. Journal of Vision, 9(2), 10, 1–8.
http://journalofvision.org/9/2/10/, doi:10.1167/9.2.10.

Russell, R. (2003). Sex, beauty, and the relative luminance of facial features, Perception, 32, 1093-1107.

Russell, R., B. Duchaine, and K. Nakayama. (2009). Super-recognizers: People with extraordinary face recognition ability. Psychonomic Bulletin & Review, 16(2), 252-257.

Russell, R. and P. Sinha. (2007). Real-world face recognition: The importance of surface reflectance properties, Perception, 36, 1368-1374.

Russell, R., P. Sinha, I. Biederman, and M. Nederhouser. (2006). Is pigmentation important for face recognition? Evidence from contrast negation, Perception, 35, 749-759.

Sex, ethnicity, and facial skin perception

Postgraduate students, School of Psychology, Cardiff University

A recent study from Cardiff University (Wales) has found interesting sex differences in the way men and women evaluate facial skin color, specifically for faces of white, black, or mixed-race origin. The female participants evaluated White faces the least favorably out of all male facial photos. Conversely, the male participants evaluated Black faces the least favorably out of all female facial photos. Participants of both sexes gave relatively low ratings to White faces for a wide range of characteristics (attractiveness, competence, dominance, warmth, maturity, strength, masculinity).

Previous research has suggested that perceived attractiveness and personality are affected by the race such that White faces are more attractive but less masculine than Black faces. Such studies, however, have been based on very small stimulus sets. The current study investigated perceived attractiveness and personality for 600 Black, White and mixed-race faces. Many of the investigated personality traits were correlated with race when rated by White participants. Attractiveness specifically was greater for Black male faces than White male faces and among mixed-race faces. Blackness correlated with increased attractiveness. A reverse pattern was found for female faces with Whiteness being associated with attractiveness. The results are discussed in terms of the sexual dimorphism demonstrated in skin color. (Lewis 2010)

These findings are partially consistent with previous studies:

Feinman & Gill 1978
When a thousand American students were surveyed on their physical preferences in the opposite sex, 30% of the males versus 10% of the females disliked black skin. Conversely, 56% of the males versus 82% of the females disliked very light skin.

van den Berghe & Frost 1986
According to a cross-cultural survey, lighter skin is more strongly preferred for women than for men in all culture areas.

Frost 1994
Women have varying preferences over the menstrual cycle when choosing between human faces that differ slightly in skin tone. When pairs of male faces are shown, the darker face is more strongly preferred by participants in the first two-thirds of the cycle (high ratio of estrogen to progesterone) than by those in the last third (low estrogen/progesterone ratio). In contrast, when pairs of female faces are shown, skin-tone preference remains unchanged throughout the cycle.

Nonetheless, Lewis (2010) differs from these previous studies on three points:

1). The participants were asked to evaluate major differences in human skin color that clearly have racial/ethnic significations. In contrast, the previous studies examined how men and women evaluate minor differences. Van den Berghe and Frost (1986) found a cross-cultural preference for lighter-skinned women, but only in the sense of their being lighter than average for the local population. Similarly, Frost (1994) only examined female response to minor differences in skin tone.

2). Dark skin was generally preferred. This preference was merely stronger for male faces than for female faces. In contrast, van den Berghe and Frost (1986) found that light skin was generally preferred, with this preference being stronger in response to female faces. Frost (1994) likewise found that light skin was generally preferred, with this preference being weaker with regard to male faces during the first two-thirds of the menstrual cycle. Even then, the lighter male face remained the more popular of the two.

3). There was no control for phase of menstrual cycle. The sex difference in preference would probably have been greater if the author had excluded those female participants who were in the last third of the menstrual cycle.

The first point probably explains the second one. The author examined how men and women respond to major differences in skin color, and such differences have meanings that go far beyond sexual aesthetics. Because the white British participants had to choose among very divergent skin colors, their responses were almost certainly contaminated by ‘prejudice avoidance’, i.e., they avoided giving low ratings to non-white faces for fear of seeming prejudiced. Since anti-white prejudice is not stigmatized, the tendency would be to overcompensate—to err on the safe side.

Overcompensation is suggested by the results. Black faces were given top rating on all 7 items by the female participants and on 4 of the 7 by the male participants. White faces failed to get top rating on any item. This is particularly surprising given that all of the participants were white British. They apparently wished to avoid seeming prejudiced—even to the point of systematically rejecting their own people.

This source of bias does not invalidate the overall finding, i.e., the sex difference in face ratings. All of the participants were presumably immersed in the same ideological environment, and there is no reason to believe that prejudice avoidance is weaker in men than in women.

References

Feinman, S., & Gill, G.W. (1978). Sex differences in physical attractiveness preferences. Journal of Social Psychology, 105, 43‑52.

Frost, P. (1994). Preference for darker faces in photographs at different phases of the menstrual cycle: Preliminary assessment of evidence for a hormonal relationship, Perceptual and Motor Skills, 79, 507-514.

Lewis, M.B. (2010). Who is the fairest of them all? Race, attractiveness and skin color sexual dimorphism, Personality and Individual Differences, 50, 159-162.

Van den Berghe, P.L., & P. Frost. (1986). Skin color preference, sexual dimorphism and sexual selection: A case of gene‑culture co‑evolution? Ethnic and Racial Studies, 9, 87‑113.