Human Y-chromosome mutation rate

(corrected)

This is a very important paper that showed that 4 base substitutions occurred a length of 10 million base pairs (or about 1/6th) of the Y chromosome in two individuals separated by 13 generations. What this means is:

• Even when we are able to routinely sequence entire Y chromosomes, we will still not generally be able to tell apart fathers and sons as sons (via their Y chromosome) only sometimes have different Y chromosomes than their fathers. In a large number of cases there will be no mutations.
• On the positive side, relationships in the entire human Y-chromosome phylogeny will be resolved with an accuracy of a few generations. We will no longer have to rely on poor resolution Y-STR "genetic distance" methods to determine relatedness of individuals. The chunky huge haplogroups dominating modern Y-chromosome pools will be resolved into a hierarchy of more exclusive families and really precise patterns of migration and admixture may be inferred.

UPDATE: It occurred to me that the new mutation rate could also be used to directly infer the age of Y-chromosome Adam -and other haplogroups-, using the SNP counting method of Karafet et al. One simply needs to find out how many bases were sequenced in that study to infer the expected number of mutations/generation.

Current Biology doi:0.1016/j.cub.2009.07.032

Human Y Chromosome Base-Substitution Mutation Rate Measured by Direct Sequencing in a Deep-Rooting Pedigree

Yali Xue et al.

Abstract

Understanding the key process of human mutation is important for many aspects of medical genetics and human evolution. In the past, estimates of mutation rates have generally been inferred from phenotypic observations or comparisons of homologous sequences among closely related species [1,2,3]. Here, we apply new sequencing technology to measure directly one mutation rate, that of base substitutions on the human Y chromosome. The Y chromosomes of two individuals separated by 13 generations were flow sorted and sequenced by Illumina (Solexa) paired-end sequencing to an average depth of 11 or 20, respectively [4]. Candidate mutations were further examined by capillary sequencing in cell-line and blood DNA from the donors and additional family members. Twelve mutations were confirmed in 10.15 Mb; eight of these had occurred invitro and four invivo. The latter could be placed in different positions on the pedigree and led to a mutation-rate measurement of 3.0 10⁸ mutations/nucleotide/generation (95% CI: 8.9 10⁹7.0 10⁸), consistent with estimates of 2.3 10⁸6.3 10⁸ mutations/nucleotide/generation for the same Y-chromosomal region from published human-chimpanzee comparisons [5] depending on the generation and split times assumed.

Link

Bronze Age origin of Semitic languages

Bayesian phylogenetic methods, originally developed for biology, have been increasingly -and successfully- applied to linguistic data in recent years (e.g., for Indo-Europeans, Melanesians, and Austronesian speakers from the Pacific).

The current paper proposes a Bronze Age origin for Semitic languages, ~3 thousand years after the split of European from Anatolian Indo-European speakers. I don't find this particularly surprising, as Semitic has been, until relatively recently, much more geographically constrained than Indo-European, and -due to the early literacy of the populations of the Near East, its post-Neolithic arrival can be observed in the archaeological record itself.

It also explains a facet of Y-chromosome distribution, that I have commented on before, namely the fact that the common Near Eastern haplogroup J2 extends from Europe to South Asia in a "horizontal zone" accompanied with little of its sister clade J1, but in the Near East itself, there is a "vertical zone" from the Black and Caspian seas to Arabia of high J1 frequency. As I have explained recently, the mixed J2/J1 frequency in the central Near East is due to an enrichment with J1 lineages of a population that had (in pre-Semitic times) a high J2/J1 ratio like those of Europe, Asia Minor, and Iran. J1 should not be seen as exclusively Semitic, but it can't be denied that the major factor affecting its current spread has been the arrival of Semites from the South, the latest episode of which involved the spread of Arab Muslims.

The current study also demonstrates that linguistic Bayesian phylogenetics (LBP) has no inherent bias to produce older dates for language dispersals; while the origin of the Indo-European (IE) language family has been dated to the early European Neolithic, and now Semitic to ~6,000 years, the spread of Melanesian languages to Pleistocene times, and of the Austronesian settlement of the Pacific to ~5,000 years. The congruence between LBP and traditional archaeology in all these cases should force IE exceptionalists who cling to the old theory of "steppe horse riders" to explain why, only in the dispersal of IE, it should LBP should have failed.

The paper also has free supplementary data, including a multistate phylogeny (pdf) of Semitic languages (reproduced top left of this post).

(More details to follow after I thoroughly read the paper)

UPDATE (Aug 27):

From the paper:

Furthermore, Eblaite (no Eblaite wordlists were available for our study), the closest relative of Akkadian and the only other member of East Semitic, was spoken in the Levant (specifically the northeast Levant or present-day Syria; Gordon 1997), which is also where some of the oldest West Semitic languages were spoken (Ugaritic, Aramaic and ancient Hebrew). The presence of ancient members of the two oldest Semitic groups (East andWest Semitic) in the same region of the Levant, combined with a possible long interval (100–3000 years) between the origin of Semitic and the appearance of Akkadian in Sumer, suggests a Semitic origin in the northeast Levant and a later movement of Akkadian eastward into Mesopotamia and Sumer (see figure 1 for a map of our proposed Semitic dispersals).

An origin of Semitic in northeast Levant (Syria) would be consistent with the observed east-west cline of decreasing J1 frequency in the Levant; the authors do, however, mention that the possibility for unknown extinct languages of the Semitic language may shift both the age of the language and its place of origin.

Lacking closely related non-Semitic languages to serve as out-groups in our phylogeny, we cannot estimate when or where the ancestor of all Semitic languages diverged from Afroasiatic. Furthermore, it is likely that some early Semitic languages became extinct and left no record of their existence. This is especially probable if early Semitic societies were pastoralist in nature (Blench 2006), as pastoralists are less likely to leave epigraphic and archaeological evidence of their languages.

A pastoralist association of Semitic languages is also consistent with the observed correlation of haplogroup J1 with herders and J2 with settled farmers in the Near East.


Proc. R. Soc. B 7 August 2009 vol. 276 no. 1668 2703-2710

Bayesian phylogenetic analysis of Semitic languages identifies an Early Bronze Age origin of Semitic in the Near East

Andrew Kitchen et al.

Abstract

The evolution of languages provides a unique opportunity to study human population history. The origin of Semitic and the nature of dispersals by Semitic-speaking populations are of great importance to our understanding of the ancient history of the Middle East and Horn of Africa. Semitic populations are associated with the oldest written languages and urban civilizations in the region, which gave rise to some of the world's first major religious and literary traditions. In this study, we employ Bayesian computational phylogenetic techniques recently developed in evolutionary biology to analyse Semitic lexical data by modelling language evolution and explicitly testing alternative hypotheses of Semitic history. We implement a relaxed linguistic clock to date language divergences and use epigraphic evidence for the sampling dates of extinct Semitic languages to calibrate the rate of language evolution. Our statistical tests of alternative Semitic histories support an initial divergence of Akkadian from ancestral Semitic over competing hypotheses (e.g. an African origin of Semitic). We estimate an Early Bronze Age origin for Semitic approximately 5750 years ago in the Levant, and further propose that contemporary Ethiosemitic languages of Africa reflect a single introduction of early Ethiosemitic from southern Arabia approximately 2800 years ago.

Link

Demic diffusion of agriculture into Europe supported by craniometric data

A previous article by Pinhasi et al. Tracing the Origin and Spread of Agriculture in Europe

UPDATE (Sep 4):

A new ancient mtDNA study supports the conclusion that LBK agriculturalists were not related to the Mesolithic population.

PLoS ONE 4(8): e6747. doi:10.1371/journal.pone.0006747

Craniometric Data Supports Demic Diffusion Model for the Spread of Agriculture into Europe

Ron Pinhasi, Noreen von Cramon-Taubadel

Abstract

Background

The spread of agriculture into Europe and the ancestry of the first European farmers have been subjects of debate and controversy among geneticists, archaeologists, linguists and anthropologists. Debates have centred on the extent to which the transition was associated with the active migration of people as opposed to the diffusion of cultural practices. Recent studies have shown that patterns of human cranial shape variation can be employed as a reliable proxy for the neutral genetic relationships of human populations.

Methodology/Principal Findings

Here, we employ measurements of Mesolithic (hunter-gatherers) and Neolithic (farmers) crania from Southwest Asia and Europe to test several alternative population dispersal and hunter-farmer gene-flow models. We base our alternative hypothetical models on a null evolutionary model of isolation-by-geographic and temporal distance. Partial Mantel tests were used to assess the congruence between craniometric distance and each of the geographic model matrices, while controlling for temporal distance. Our results demonstrate that the craniometric data fit a model of continuous dispersal of people (and their genes) from Southwest Asia to Europe significantly better than a null model of cultural diffusion.

Conclusions/Significance

Therefore, this study does not support the assertion that farming in Europe solely involved the adoption of technologies and ideas from Southwest Asia by indigenous Mesolithic hunter-gatherers. Moreover, the results highlight the utility of craniometric data for assessing patterns of past population dispersal and gene flow.

Link

Lower Paleolithic hunters from Qesem Cave

From ScienceDaily:

"The Lower Paleolithic (earlier) hunters were skilled hunters of large game animals, as were Upper Paleolithic (later) humans at this site," UA anthropology professor Mary C. Stiner said.

"This might not seem like a big deal to the uninitiated, but there's a lot of speculation as to whether people of the late Lower Paleolithic were able to hunt at all, or whether they were reduced to just scavenging," Stiner said. "Evidence from Qesem Cave says that just like later Paleolithic humans, the earlier Paleolithic humans focused on harvesting large game. They were really at the top of the food chain."

PNAS doi:10.1073/pnas.0900564106

Cooperative hunting and meat sharing 400–200 kya at Qesem Cave, Israel

Mary C. Stiner et al.

Abstract

Zooarchaeological research at Qesem Cave, Israel demonstrates that large-game hunting was a regular practice by the late Lower Paleolithic period. The 400- to 200,000-year-old fallow deer assemblages from this cave provide early examples of prime-age-focused ungulate hunting, a human predator–prey relationship that has persisted into recent times. The meat diet at Qesem centered on large game and was supplemented with tortoises. These hominins hunted cooperatively, and consumption of the highest quality parts of large prey was delayed until the food could be moved to the cave and processed with the aid of blade cutting tools and fire. Delayed consumption of high-quality body parts implies that the meat was shared with other members of the group. The types of cut marks on upper limb bones indicate simple flesh removal activities only. The Qesem cut marks are both more abundant and more randomly oriented than those observed in Middle and Upper Paleolithic cases in the Levant, suggesting that more (skilled and unskilled) individuals were directly involved in cutting meat from the bones at Qesem Cave. Among recent humans, butchering of large animals normally involves a chain of focused tasks performed by one or just a few persons, and butchering guides many of the formalities of meat distribution and sharing that follow. The results from Qesem Cave raise new hypotheses about possible differences in the mechanics of meat sharing between the late Lower Paleolithic and Middle Paleolithic.

Link

John Hawks on historical trends in length of life

John Hawks has a post on Human lifespans have not been constant for the last 2000 years, in which he criticizes the idea that there has not been a substantial change in length of life in the last 2,000 years:

Syllogistically speaking, Socrates didn't die of natural causes, therefore the Greeks had lifespans the same as ours. Or something.

...

But there's no doubt that Romans, Egyptians, and Greeks were dropping dead at age 30, 40, 50 and 60 -- at much higher age-specific mortality rates than today. Estimating the overall age profile is difficult and requires models.

Fortunately, there has been a study of the length of life in ancient Greece, that shows, that Socrates was not a unique case:

In a study of all men of renown, living in the 5th and 4th century in Greece, we identified 83 whose date of birth and death have been recorded with certainty. Their mean +/- SD and median lengths of life were found to be 71.3+/-13.4 and 70 years, respectively.

Of course, the lifespan of "men of renown" should be correlated with that of the general population, but with a higher mean, since men require time to achieve "renown". But, certainly the figure of 71 years does not seem too different from that of more recent men of renown, which is perhaps more surprising if one accounts for the high levels of violence in ancient Greece.

UPDATE I

John also writes:

More important, we don't have a clue what the maximum lifespan may have been 200, 500, or 2000 years ago. Such a tiny fraction of people make it above age 100 today that we could hardly expect to find any of them at all from skeletal samples. Nor can we expect accurate ages from historical records -- Methuseleh, anyone?

We do have some fairly secure dates for at least some ancient individuals. Strabo died at 88. Sophocles died at 90. Democritus' life span was said to be anything from 90-109. Alexis, the comic poet reached the age of 100, Isocrates, 98. So, there were probably centenarians in ancient times, although what the maximum was is anyone's guess.

UPDATE II

Psalm 90:10 gives the length of life as 70.

The days of our years are three score years and ten; and if by reason of strength they be fourscore years, yet is their strength labor and sorrow; for it is soon cut off, and we fly away.

Herodotus (1.32) has Solon give the "limit of life" at 70.

Croesus, you ask me about human affairs, and I know that the divine is entirely grudging and troublesome to us. [2] In a long span of time it is possible to see many things that you do not want to, and to suffer them, too. I set the limit of a man's life at seventy years;

This suggests to me that a length of life of 70 was formulaic in the ancient Mediterranean, and corresponds quite well with the average recorded length for prominent Greeks.

UPDATE III

Plato, in the Laws introduces a law that the guardians should rule from age 50 to at most the age of 70. Since the Laws is a work of political reform, we can assume that common Greek practice of the day (which is corroborated by historical knowledge about old-age statesmen) allowed for much older rulers, and, hence, such individuals existed in fairly substantial numbers -so that their rulership would become the object of a formal prohibition.

Aristotle, comments (in the History of Animals) that:

The reproductive function in men usually continues active till they are sixty years old; if they pass beyond this period, till they are seventy; and some men have had children at seventy years old.

In a famous passage of the Politics, after noting that male and female generation length is at most 50 and 70, he prescribes the ideal marriage age:

Women should marry when they are about eighteen years of age, and men at seven and thirty.

The prescription to marry at 37, suggests that early death must not have been too common; otherwise, it would be difficult to maintain the population's numbers, a topic which clearly occupied Aristotle, who commented on Sparta's oligandria in the same work.

UPDATE IV:

Lucian's Macrobii is dedicated to the topic of long-lived men, after listing the ages of various ancient and semi-mythical people, gives the ages at death of several historical individuals, including some fairly reliable ones:

Gorgias, 108

Of the orators, Gorgias, whom some call a sophist, lived to be one hundred and eight, and starved himself to death. They say that when he was asked the reason for his great age, sound in all his faculties, he replied that he had never accepted other peoples invitations to dinner!

Ctesibius, 104

Of the historians, Ctesibius died at the age of one hundred and four while taking a walk, according to Apollodorus in his Chronology.

Hieronymus, 104

Hieronymus, who went to war and stood much toil and many wounds, lived one hundred and four years, as Agatharchides says in the ninth book of his History of Asia; and he expresses his amazement at the man, because up to his last day he was still vigorous in his marital relations and in all his faculties, lacking none of the symptoms of health.

UPDATE V (Aug 31)

A reader writes in the comments:

The maximum life expectancy for humans seems to have been about 120years throughout recorded history.

"My Spirit will not strive with man forever, for he is indeed flesh; yet his days shall be one hundred and twenty years." Genesis 6:3

"From Cicero’s death to our day is a hundred and twenty years, one man’s life-time." Tacitus, "A Dialogue on Oratory", 17. Tacitus writes of seeing a 120 year old man in Britain in the 1st century A.D.

120 years as a length of exceptionally long-lived people is also mentioned by Herodotus:

The Icthyophagi then in their turn questioned the king concerning the term of life, and diet of his people, and were told that most of them lived to be a hundred and twenty years old, while some even went beyond that age- they ate boiled flesh, and had for their drink nothing but milk.

Of course we can't take the veracity of this story at face value, but the choice of number may suggest that it is as great as it could be without becoming unbelievable to the audience.

Admixture in northeastern Mexico

J Hum Genet. 2009 Aug 14. doi:10.1038/jhg.2009.65.

Ancestry informative markers and admixture proportions in northeastern Mexico

Martinez-Fierro ML, Beuten J, Leach RJ, Parra EJ, Cruz-Lopez M, Rangel-Villalobos H, Riego-Ruiz LR, Ortiz-Lopez R, Martinez-Rodriguez HG, Rojas-Martinez A.

To investigate the ancestral admixture in the Mestizo population in northeastern Mexico, we genotyped 74 ancestral informative markers (AIMs) and 15 Y-single-nucleotide polymorphisms (Y-SNPs) in 100 individuals. The Native American contribution is 56% (range: 27.4-81.2%), the European contribution is 38% (range: 16.7-70.5%) and the West African contribution is 6%. The results show a higher European contribution than was reported in other similar studies in the country, albeit with a predominant Native American ancestry. No remarkable differences in the ancestry proportions were observed using subgroups of 74, 54, 34 and 24 AIMs. The paternal lineage calculated by genotyping of 15 Y-SNPs, shows a major component of European and Eurasian ancestry markers ( approximately 78%), compared with Amerindian ( approximately 12%) and African markers (10%). This information will set a reference for future determinations of admixture proportions in the Mestizo population from Mexico and for population-based association studies of complex diseases.

Link

Amerindian mtDNA in Argentinean population

Int J Legal Med. 2009 Aug 13. [Epub ahead of print]

Amerindian mitochondrial DNA haplogroups predominate in the population of Argentina: towards a first nationwide forensic mitochondrial DNA sequence database.

Bobillo MC, Zimmermann B, Sala A, Huber G, Röck A, Bandelt HJ, Corach D, Parson W.

The study presents South American mitochondrial DNA (mtDNA) data from selected north (N = 98), central (N = 193) and south (N = 47) Argentinean populations. Sequence analysis of the complete mtDNA control region (CR, 16024-576) resulted in 288 unique haplotypes ignoring C-insertions around positions 16193, 309, and 573; the additional analysis of coding region single nucleotide polymorphisms enabled a fine classification of the described lineages. The Amerindian haplogroups were most frequent in the north and south representing more than 60% of the sequences. A slightly different situation was observed in central Argentina where the Amerindian haplogroups represented less than 50%, and the European contribution was more relevant. Particular clades of the Amerindian subhaplogroups turned out to be nearly region-specific. A minor contribution of African lineages was observed throughout the country. This comprehensive admixture of worldwide mtDNA lineages and the regional specificity of certain clades in the Argentinean population underscore the necessity of carefully selecting regional samples in order to develop a nationwide mtDNA database for forensic and anthropological purposes. The mtDNA sequencing and analysis were performed under EMPOP guidelines in order to attain high quality for the mtDNA database.

Link

Comparison of Neanerthal and modern human diets

PNAS doi:10.1073/pnas.0903821106

Isotopic evidence for the diets of European Neanderthals and early modern humans

Michael P. Richards, Erik Trinkaus

Abstract

We report here on the direct isotopic evidence for Neanderthal and early modern human diets in Europe. Isotopic methods indicate the sources of dietary protein over many years of life, and show that Neanderthals had a similar diet through time (≈120,000 to ≈37,000 cal BP) and in different regions of Europe. The isotopic evidence indicates that in all cases Neanderthals were top-level carnivores and obtained all, or most, of their dietary protein from large herbivores. In contrast, early modern humans (≈40,000 to ≈27,000 cal BP) exhibited a wider range of isotopic values, and a number of individuals had evidence for the consumption of aquatic (marine and freshwater) resources. This pattern includes Oase 1, the oldest directly dated modern human in Europe (≈40,000 cal BP) with the highest nitrogen isotope value of all of the humans studied, likely because of freshwater fish consumption. As Oase 1 was close in time to the last Neanderthals, these data may indicate a significant dietary shift associated with the changing population dynamics of modern human emergence in Europe.

Link

Carleton Coon on video

The Penn Museum has put up "What in the Word", a series from the 1950s, in which a group of panelists (one of which is physical anthropologist Carleton Coon) discuss various artifacts in the context of world archaeology/anthropology/history.

Here is the first episode:

Diet in southern French Neolithic populations

American Journal of Physical Anthropology doi:10.1002/ajpa.21141

Southern French Neolithic populations: Isotopic evidence for regional specificities in environment and diet

Estelle Herrscher, Gwenaëlle Le Bras-Goude

Abstract

The Middle Neolithic of the Northwestern Mediterranean area (4500-3500 BC cal) is characterized by the development of food production techniques as well as by increasing social complexity. These characteristics could have had an impact on human dietary patterns. To evaluate human dietary practices and lifeways of the Middle Neolithic populations from the South of France, stable carbon and nitrogen isotope analysis was carried out on 57 human and 53 faunal bones from seven archaeological sites located in the Languedoc and Garonne regions between 20 and 100 km from the Mediterranean Sea, respectively. Results show regional differences in carbon isotope values. Animal and human bones from the Languedoc region are significantly enriched in ¹³C relative to the Garonne. Conversely, human and dog bones from the Garonne region are significantly enriched in ¹⁵N compared to human and dog bones from the Languedoc region. These results highlight the importance of the local ecosystem in human and animal diet as well as a regional differentiation of palaeodietary behavior, which probably relates to economic and social factors. The comparison of stable isotope data with archaeological and biological evidence does not show any significant intra- or interpopulation differences. However, the presence of human outliers suggests that migration probably occurred, perhaps in relation to the trade of animals and/or materials. This study also highlights the importance of investigating local animal stable isotope values for the interpretation of human palaeodiet.

Link

Post-glacial recolonization of Britain happened after 14,700 years BP

Quaternary Science Reviews
Volume 28, Issues 19-20, September 2009, Pages 1895-1913
doi:10.1016/j.quascirev.2009.03.006

The early Lateglacial re-colonization of Britain: new radiocarbon evidence from Gough's Cave, southwest England


R.M. Jacobi and T.F.G. Higham

Abstract

Gough's Cave is still Britain's most significant Later Upper Palaeolithic site. New ultrafiltered radiocarbon determinations on bone change our understanding of its occupation, by demonstrating that this lasted for only a very short span of time, at the beginning of the Lateglacial Interstadial (Greenland Interstadial 1 (GI-1: Bølling and Allerød)). The application of Bayesian modelling to the radiocarbon dates from this, and other sites from the period in southwest England, suggests that re-colonization after the Last Glacial Maximum took place only after 14,700 cal BP, and is, therefore, more recent than that of the Paris Basin and the Belgian Ardennes. On their own, the radiocarbon determinations cannot tell us whether re-colonization was synchronous with, just prior to, or after, Lateglacial warming. Isotopic studies of humanly-modified mammalian tooth enamel may be one way forward.

Link

John Hawks on Anne Wojcicki on Race

John Hawks comments on an interview by Anne Wojcicki, one of the founders of 23andMe.

In the interview:

A lot of the difficulty in talking about race has been a lack of agreement on what “race” means. In the past, the idea of pure races also included an ordering of certain races as inherently superior to others. We reject this idea absolutely. However, that doesn’t mean that there are no genetic differences between populations of different ancestral origin. A few of our features use the genome-wide data of reference populations from around the world to trace the origin of pieces of an individual’s genome. Some customers have complex patterns depending on where their ancestors originated. These reference populations aren’t “races”; they’re representative samples of peoples who have lived in a single place for a very long time and have thus accumulated different sets of genetic variants over time.

John comments:

That's a tricky piece of wordcraft -- they're not 'races'; "they're representative samples of peoples who have lived in a single place for a very long time and have thus accumulated different sets of genetic variants over time."
Uhh....I'm thinking that's pretty much the definition of race in a lot of textbooks...

The points she starts with -- both true -- are that human populations aren't isolated ("pure races"), and you shouldn't rank them ("inherently superior"). But those ideas conflict with the process, since the software commonly used in human genetics (like STRUCTURE and other programs) assumes a model in which originally isolated groups (otherwise known as pure races) mix together.

It is true that STRUCTURE (and similar tools) use a model in which each individual is assumed to have a share of genes from each of K different populations, that differ from each other in the frequency (and in some case co-occurrence, due to linkage) of different gene variants.

These K populations, are not, however, assumed to be "pure races", but rather simply populations that differ from each other in their genetic characteristics. The program itself does not make any assumptions as to why they differ from each other: it could be due to different types or intensity of gene flow, or to reproductive isolation. Distinctive gene frequencies may arise both due to "race purity" or in the presence of gene flow, provided that it occurs at a low enough level so that changes that occur in one population are not reflected immediately in the other, and their distinctiveness is maintained.

But, more importantly, the "pure races" model is an approximation whose validity can be checked. If gene flow is substantial, then our simplifying STRUCTURE view of the world will not result in distinct clusters, in which the great majority of individuals from a particular population have the greatest share of their ancestry from the same racial clusters.

In other words, the fact that we assume distinct "pure" clusters is no guarantee that we will get distinct races via an application of STRUCTURE. Try STRUCTURE with K=2 in a homogeneous population, and you won't get 2 distinct clusters, even though you made that assumption: you will get a bunch of individuals that belong -in various proportions- to the 2 clusters, but no 2 solid blocks of individuals, one of which belongs predominantly to the first, and the other to the second cluster.

What STRUCTURE and similar programs have repeatedly shown, is that humans do, in fact, have genomes that resemble each other in the way we would expect if there were pure races which have occasionally mixed in their peripheries.

Our understanding of genetic processes helps us understand, that this is not the result of separate creation of human races, but of long-term gene flow limitations due to geography and culture, that have allowed originally related human populations to evolve apart.

In contrast with a Gobineau-istic view of set primordial races becoming ever more mixed and indistinct, our modern understanding is that human races evolved in historical time, becoming ever more distinct and separate. This is not inevitable, and human history has been punctuated by episodes of intermixture as well as separation, but the overall thrust has been one of diversification and increased distinctness, which may, perhaps, be set back in the modern age due to increased ease of transporation.

Male-female differences in craniofacial dimensions of Koreans

J Craniofac Surg. 2009 Mar;20(2):356-61.

Female-to-male proportions of the head and face in Koreans.

Song WC, Kim JI, Kim SH, Shin DH, Hu KS, Kim HJ, Lee JY, Koh KS.

It is well known that the head and face are smaller in female subjects than in male subjects. However, almost all previous studies have quantified the size difference between female and male subjects as simple numerical values, which might not clarify the difference. The present study evaluated the female-to-male proportions of the head and face so as to clarify the sex-related differences. A total of 1939 female subjects and 1398 male subjects were divided into 3 age groups: young (20-39 y), middle-aged (40-59 y), and elderly (60-79 y). The dimensions were classified into 3 categories: 5 cephalic, 3 frontal facial, and 6 lateral facial. The female-to-male proportions of individual dimensions were compared in the 3 age groups using the following formula: female measurement value x 100/(mean of male measurement value). The female-to-male proportions of the cephalic dimension increased with age, with the female cephalic dimensions overall being about 96% of the male cephalic dimensions. The female-to-male proportions of the frontal facial dimension were constant across the age groups, with the female frontal facial dimensions overall being 95% of the male frontal facial dimensions. The female lateral facial dimension increased markedly from the young to middle-aged group and was constant or decreased slightly from the middle-aged to the elderly group. Overall, the female lateral facial dimensions were approximately 97% of the male lateral facial dimensions. The present study will suggest a new approach to elucidate those sex-related dimensional differences that are characteristic of female and male subjects.

Link

East vs. West differences in facial expressions

Related podcast in Scientific American: Facial Expressions: East Doesn't Meet West

Current Biology, doi:10.1016/j.cub.2009.07.051

Cultural Confusions Show that Facial Expressions Are Not Universal

Rachael E. Jack

Abstract

Central to all human interaction is the mutual understanding of emotions, achieved primarily by a set of biologically rooted social signals evolved for this purposefacial expressions of emotion. Although facial expressions are widely considered to be the universal language of emotion [1,2,3], some negative facial expressions consistently elicit lower recognition levels among Eastern compared to Western groups (see [4] for a meta-analysis and [5,6] for review). Here, focusing on the decoding of facial expression signals, we merge behavioral and computational analyses with novel spatiotemporal analyses of eye movements, showing that Eastern observers use a culture-specific decoding strategy that is inadequate to reliably distinguish universal facial expressions of fear and disgust. Rather than distributing their fixations evenly across the face as Westerners do, Eastern observers persistently fixate the eye region. Using a model information sampler, we demonstrate that by persistently fixating the eyes, Eastern observers sample ambiguous information, thus causing significant confusion. Our results question the universality of human facial expressions of emotion, highlighting their true complexity, with critical consequences for cross-cultural communication and globalization.

Link

Mediterranean diet, physical activity, and Alzheimer's disease

The article is freely viewable.

JAMA 302(6):627-637.

Physical Activity, Diet, and Risk of Alzheimer Disease

Nikolaos Scarmeas et al.

Abstract<

Context Both higher adherence to a Mediterranean-type diet and more physical activity have been independently associated with lower Alzheimer disease (AD) risk but their combined association has not been investigated.

Objective To investigate the combined association of diet and physical activity with AD risk.

Design, Setting, and Patients Prospective cohort study of 2 cohorts comprising 1880 community-dwelling elders without dementia living in New York, New York, with both diet and physical activity information available. Standardized neurological and neuropsychological measures were administered approximately every 1.5 years from 1992 through 2006. Adherence to a Mediterranean-type diet (scale of 0-9; trichotomized into low, middle, or high; and dichotomized into low or high) and physical activity (sum of weekly participation in various physical activities, weighted by the type of physical activity [light, moderate, vigorous]; trichotomized into no physical activity, some, or much; and dichotomized into low or high), separately and combined, were the main predictors in Cox models. Models were adjusted for cohort, age, sex, ethnicity, education, apolipoprotein E genotype, caloric intake, body mass index, smoking status, depression, leisure activities, a comorbidity index, and baseline Clinical Dementia Rating score.

Main Outcome Measure Time to incident AD.

Results A total of 282 incident AD cases occurred during a mean (SD) of 5.4 (3.3) years of follow-up. When considered simultaneously, both Mediterranean-type diet adherence (compared with low diet score, hazard ratio [HR] for middle diet score was 0.98 [95% confidence interval {CI}, 0.72-1.33]; the HR for high diet score was 0.60 [95% CI, 0.42-0.87]; P = .008 for trend) and physical activity (compared with no physical activity, the HR for some physical activity was 0.75 [95% CI, 0.54-1.04]; the HR for much physical activity was 0.67 [95% CI, 0.47-0.95]; P = .03 for trend) were associated with lower AD risk. Compared with individuals neither adhering to the diet nor participating in physical activity (low diet score and no physical activity; absolute AD risk of 19%), those both adhering to the diet and participating in physical activity (high diet score and high physical activity) had a lower risk of AD (absolute risk, 12%; HR, 0.65 [95% CI, 0.44-0.96]; P = .03 for trend).

Conclusion In this study, both higher Mediterranean-type diet adherence and higher physical activity were independently associated with reduced risk for AD.

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Coastal-inland differences in Y chromosomes of the Levant

More on this after I get a hold of and digest the information in the paper.

Just a quick comment, based only on the abstract, that the Levantine populations should be studied in a European context as well, as they have been influenced by prehistoric populations from the Aegean, Greeks, Romans, medieval Crusaders, or Ottomans of various origins.

UPDATE: The paper has several supplementary figures and tables.

In Figure S1 we see the biallelic markers used in this study, and their representation in the various populations. It is a chronic problem with studies of this sort to undertype samples; there are phylogeographically informative markers within haplogroups G, L, E1b1b, and J2 for example, which would have added important information about the specific affinities of these haplogroups in the studied populations.


Inspit of these deficiencies, we may still make some useful observations. For example, IE-speaking Iranians have largely the same haplogroups as Arabs, but a much higher representation of haplogroup J2 compared to J1. The converse is true for all Arabs except the Lebanese. But, we do know, that even in Lebanon itself, Muslims have a higher J1/J2 ratio than Christians, and Islam was the main vehicle of Arabization in the region. The Christians are descended from the pre-Arab Byzantine Greco-Aramaic populations (with an addition of Western European Y-chromosomes in some Christian communities, which would not have substantially upset the J1/J2 balance).

It is fairly clear to me that in the Middle East, Greek and Iranian-settled regions have a higher J2/J1 ratio than regions with solid Semitic or NE Caucasian populations where J1 predominates.

UPDATE II (Aug 27):

The paper reports a near zero frequency of haplogroup J1 in Tunisia and Morocco, after an earlier study by the same authors. However, a different study (Onofri et al.) on Moroccan and Tunisian Y chromosomes report 20 and 35% respectively, which is in agreement with an earlier study on North African Y-chromosomes (Arredi et al.) The discrepancy in the J1 frequency seems too large to have arisen by chance given the sample sizes, and it would be interesting to see how it may have arisen.

Annals of Human Genetics doi:10.1111/j.1469-1809.2009.00538.x

Geographical Structure of the Y-chromosomal Genetic Landscape of the Levant: A coastal-inland contrast

Mirvat El-Sibai et al.

Abstract

We have examined the male-specific phylogeography of the Levant and its surroundings by analyzing Y-chromosomal haplogroup distributions using 5874 samples (885 new) from 23 countries. The diversity within some of these haplogroups was also examined. The Levantine populations showed clustering in SNP and STR analyses when considered against a broad Middle-East and North African background. However, we also found a coastal-inland, east-west pattern of diversity and frequency distribution in several haplogroups within the small region of the Levant. Since estimates of effective population size are similar in the two regions, this strong pattern is likely to have arisen mainly from differential migrations, with different lineages introduced from the east and west.

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