Craniofacial study of the Jomon of Japan

American Journal of Physical Anthropology doi:10.1002/ajpa.20985

Regional differences in craniofacial diversity and the population history of Jomon Japan

Tsunehiko Hanihara, Hajime Ishida

Abstract

The people associated with the Jomon culture, the Neolithic inhabitants of Japan, are one of the key groups in the population history of East Asia, because they retain many archaic characters that may be traced back to Eurasian Upper Palaeolithic hunter-gatherers. In this study, the regional diversity of the Jomon skeletal series was estimated by applying the R-matrix method to 34 craniofacial measurements. The patterns of intraregional variation indicate little effect on the genetic structure of the Jomon from long-term gene flow stemming from an outside source. The regional diversities were further estimated by pooling all individuals into regional aggregates, and by computing the mean variance within local groups in each region. Although the pattern of phenotypic variation differs depending on the unit of analysis, the gradient of the diversity retains its identity. The Hokkaido region, the northernmost part of the Japanese archipelago, has the highest variance, followed by the regions of eastern Japan, while the southwestern regions have the lowest variance. These findings suggest that the Jomon ancestors of the northern part of Japan might have expanded southward to Honshu Island. Global analyses including samples from Eurasia, Africa, and Australia dating roughly to the same chronological periods as those of the Jomon samples, indicate that the Jomon cranial series share part of their ancestral gene pool with early northeastern Asians. The present findings support the archeologically suggested population growth and expansion in the northern half of the Eurasian continent during the late Pleistocene and early Holocene periods.

Link

Anatomically modern humans outcompeted Neanderthals

There have been many Neanderthal stories this year. Here is a list:

1. Did Cannibalism contribute to Neanderthal extinction?
2. Archaeology magazine interview with John Hawks
3. Divergence of modern humans and Neanderthals
4. FOXP2 and Neanderthals revisited
5. Complete Neanderthal mtDNA sequence
6. Neanderthals grew fast, matured later (?)
7. Reconstruction of female Neanderthal
8. John Hawks stars in the "Neanderthal Code"!
9. Neanderthals' trips to the sea in search of food
10. Neanderthals and the Uluzzian
11. Why did Neanderthals have broad noses?
12. The Middle to Upper Paleolithic record of western Eurasia
13. Belgian Spy Neanderthals 36,000 years BP old

Personally, I am in favor of explanations about Neanderthal demise that involve anatomically modern humans (AMHs), rather than "internal" processes such as #1 in the above list. After all, Neanderthals had been around for tens of thousands of years before they went extinct, and their extinction roughly coincided with the arrival of AMHs. That can't be a coincidence.

Did they die out due to competition? Or does their disappearance signal their genetic absorption by AMHs?

The fact of Neanderthals' extinction is highly significant. Europe could quite easily have supported both species if their population numbers were fairly low, approaching what John Hawks has described as "biblical models of human migration, like Noah-and-the-Flood level bottlenecks. " Competition increases as the ratio of resources/population increases. A live and let live attitude prevails if there is plenty for all.

It seems to me that for AMHs to either (i) absorb with almost no trace or (ii) displace/drive to extinction, the indigenous Neanderthal population of Europe, it would be necessary for a great number of AMHs to exist. Even if AMHs had a major technological/cognitive advantage -and the latest research suggests otherwise, e.g., #6, 8, 9- such a thorough dominance would be unlikely. At the very least, we might expect Neanderthals to have survived for a much longer period.

PLoS ONE doi:10.1371/journal.pone.0003972

Neanderthal Extinction by Competitive Exclusion

William E. Banks et al.

Abstract

Background

Despite a long history of investigation, considerable debate revolves around whether Neanderthals became extinct because of climate change or competition with anatomically modern humans (AMH).

Methodology/Principal Findings

We apply a new methodology integrating archaeological and chronological data with high-resolution paleoclimatic simulations to define eco-cultural niches associated with Neanderthal and AMH adaptive systems during alternating cold and mild phases of Marine Isotope Stage 3. Our results indicate that Neanderthals and AMH exploited similar niches, and may have continued to do so in the absence of contact.

Conclusions/Significance

The southerly contraction of Neanderthal range in southwestern Europe during Greenland Interstadial 8 was not due to climate change or a change in adaptation, but rather concurrent AMH geographic expansion appears to have produced competition that led to Neanderthal extinction.

Link

2008 in review: Ethnicity Strikes Back

The major breakthrough of 2008 was the application of microarray technology to the problem of inferring ethnic ancestry.

At the beginning of this year, it may have been tenable to consider ethnic groups as mere cultural constructs, divorced from nature; at its conclusion, this opinion has been conclusively falsified.

It is now clear that ethnic groups are not only cultural-political formations, but also (at least in part) distinct biological entities, emerging naturally as clusters of similarity from the genetic continuum.

1. 300K SNP paper on European genetic substructure
2. New paper on genomic differences between Ashkenazi Jews and Europeans
3. New study on global human variation based on SNPs and CNVs
4. Huge paper on human genetic relationships based on 650K SNPs
5. 500K SNP study of Oceanian populations
6. 500K SNP Europe-wide study of genetic structure
7. Population structure in Japan with 140k SNPs
8. Genetic structure in Northern Europe with 250K SNPs
9. Geography and Genetic structure in Europe (again)
10. European population structure with 300K SNPs and 6,000 individuals
11. Genomic substructure in Finns

Y chromosomes of the Gagauz

Am J Hum Biol. 2008 Dec 23. [Epub ahead of print]

Searching for the origin of Gagauzes: Inferences from Y-chromosome analysis.

Varzari A, Kharkov V, Stephan W, Dergachev V, Puzyrev V, Weiss EH, Stepanov V.

The Gagauzes are a small Turkish-speaking ethnic group living mostly in southern Moldova and northeastern Bulgaria. The origin of the Gagauzes is obscure. They may be descendants of the Turkic nomadic tribes from the Eurasian steppes, as suggested by the "Steppe" hypothesis, or have a complex Anatolian-steppe origin, as postulated by the "Seljuk" or "Anatolian" hypothesis. To distinguish these hypotheses, a sample of 89 Y-chromosomes representing two Gagauz populations from the Republic of Moldova was analyzed for 28 binary and seven STR polymorphisms. In the gene pool of the Gagauzes a total of 15 Y-haplogroups were identified, the most common being I-P37 (20.2%), R-M17 (19.1%), G-M201 (13.5%), R-M269 (12.4%), and E-M78 (11.1%). The present Gagauz populations were compared with other Balkan, Anatolian, and Central Asian populations by means of genetic distances, nonmetric multidimentional scaling and analyses of molecular variance. The analyses showed that Gagauzes belong to the Balkan populations, suggesting that the Gagauz language represents a case of language replacement in southeastern Europe. Interestingly, the detailed study of microsatellite haplotypes revealed some sharing between the Gagauz and Turkish lineages, providing some support of the hypothesis of the "Seljuk origin" of the Gagauzes. The faster evolving microsatellite loci showed that the two Gagauz samples investigated do not represent a homogeneous group. This finding matches the cultural and linguistic heterogeneity of the Gagauzes well, suggesting a crucial role of social factors in shaping the Gagauz Y-chromosome pool and possibly also of effects of genetic drift.

Link

Merry Christmas

Math gender gap news

A couple of new papers have appeared recently, which paint two different pictures of the gender gap in science/math ability.

The New Scientist reports on the first one:

Why are there so few female Einsteins? Many people share a belief that while women can do science, there are far fewer women than men at the very top of the science hierarchy because women just aren't as innately good at science as men. Others feel this view is wrong but cannot easily put their finger on why.

They should be able to now. There are few women at the top of science because there are so few women in science. It's simple statistics.

...

To test this idea, Bilalic's team checked the records of the German chess federation – in which males outnumbered females 16 to one. They found that the statistical effect of this difference in numbers accounted for 96% of the observed difference in performance between the sexes. "There is little left for biological differences to explain," says Bilalic.

While statistics may explains the absence of females at the top, they don't explain why there are fewer females in the first place. If this is due to any innate differences in chess ability between the sexes it would have to influence whether children start to play the game at all, because the dropout rates for girls and boys once they do start are similar.

The sentence in bold, of course, undermines the whole argument. The pool of male chess players is much larger than the corresponding pool of female chess players. Hence, it cannot be assumed that male and female chess players represent random samples of the same portion of the ability curve.

To give a different example, there are probably far fewer female than male lumberjacks or miners. Those that exist may be every bit as good at their job as their male counterparts. But, the fact that there are so few of them isn't so much a question of preference, but of the physiological fact that men are on average much better at mining or cutting trees.

Women were, of course, denied access to certain occupations in the past. But, nowadays, and for several generations, women have had access to the professions and higher education, so it is becoming less tenable that their under-representation in science and math achievement is due to their lack of preference for these fields, rather than a small difference in ability, manifesting itself strongly at the high end of the ability curve.

The second paper undermines the thesis of the first, by demonstrating inherent differences between male and female non-verbal infants. From ScienceDaily:

"We've known for approximately 30 years that men and women can see an object from one perspective and then recognize that object after it has been rotated in space into a new position," said David S. Moore, professor of psychology at Pitzer College and Claremont Graduate University, both in Claremont, Calif., and an expert in the development of perception and cognition in infants. "In addition, while we have known that all people can do this, it turns out that men are quite a bit faster at it than women are. Previous studies have shown that this sex difference can be detected in children as young as 4 years of age, but our study is the first to have successfully found a way to assess the situation in young infants.

"Although we did not expect to find any sex differences in babies this young, our results suggest that the 5-month-old boys in our study used mental rotation to complete our task while the 5-month-old girls in our study did not," Moore said.

On the same subject, La Griffe du Lion has posted an analysis on the Math Sex Gap Revisited: a theory for everyone:

At the annual meeting of Women Against the Gap, Prodigy unveils a model of mathematical ability that brings together seemingly isolated facts. He demonstrates that there is a single math ability gap between the sexes, biological in origin, and independent of race, culture and geography. Prodigy introduces the theory of Everyone which accounts for all available data.

Expansion of E-V13 and I-M423 from the Balkans

The most interesting aspect of this paper is that it supports a European rather than Middle Eastern origin of E-V13 and I-M243 based on an analysis of relative Y-STR variance. However, the age estimates presented in this paper are based on the infamous "evolutionary mutation rate", and are thus suspect. What appears as "Mesolithic" using the wrong mutation rate is actually Bronze Age, although with hefty confidence intervals.

Furthermore, caution should be used when correlating TMRCA with archaeological events. As I have noted before, the founder of a haplogroup is not the same as the Most Recent Common Ancestor (MRCA) of the present-day population from that haplogroup. This study seems to argue against the Middle Eastern origin of E-V13 suggested by Cruciani et al..

When exactly E-V13 came to the Balkans remains to be seen, but its expansion is properly placed in a Bronze Age rather than Mesolithic time frame. Interestingly, the paper has turned up some additional evidence:

Only four E-M78*, which do not belong to any already described sub-clade, have been observed in the southern Balkans. Two of them (from Greece) turned out to be characterized by the mutation M521 and therefore represent a new M78 lineage.

...

The presence of E-M78^* Y chromosomes in the Balkans (two Albanians), previously described virtually only in northeast Africa, upper Nile, gives rise to the question of what the original source of the E-M78 may have been.

This is suggestive that E-V13 expanded from the Balkans out of a pre-existing E-M78 ancestor, almost completely swamping that E-M78 population. When exactly E-M78 arrived in the Balkans, it is difficult to say, since Y-STR variance takes us only as far back as the MRCA who lived in the Bronze Age.

In any case, this paper adds important new data on Balkan Y-chromosomes, although it is unfortunately marred by facile Y-chromosome/archaeological correlations, and the use of the inappropriate evolutionary mutation rate.

At present, I see no reason to change my theory on the expansion of E-V13. The finding that E-V13 is less diverse in Anatolia and the Middle East further reinforces the idea of the Balkan origin of that expansion, while an estimated age in the 2nd millennium BC is consistent with the birth of the Greek world.

The authors write:

Interestingly, J-DYS445-6 and J-M92 (a sub-lineage of M67), both have expansion times between 7000 and 8000 years ago

Converted into non-"evolutionary" ages, these are again consistent with the expansion of the Greek world. J-M92 was correctly associated with the expansion of the Greek world by Di Giacomo et al. (2004) "Y chromosomal haplogroup J as a signature of the post-neolithic colonization of Europe", who did not fall into the evolutionary mutation rate trap.

Also of interest is the discovery of an extremely rare R1a*(xR1a1) in a single Macedonian Greek. Another instance of R1a*(xR1a1) was previously discovered in a Cretan Greek. R1a1 occurred in 16.3% of Greeks from Athens vs. 10.5% of Greeks from Macedonia, the opposite of what was observed by Semino et al. in 2000. R1a1 does not seem to have any clear geographical structure within Greece, which would be expected if it was of more recent introduction.

UPDATE: Having labeled E-V13 Mesolithic, the authors label haplogroups G and J2 as Neolithic. A most interesting observation (Table 1) is that haplogroup J2a-M410* and J2b-M12* have the maximum and second maximum Y-STR variance in the region, being much more diverse than other haplogroups supposedly representing pre-agricultural Europeans.

At least, such a finding should give pause to those who arrive at facile conclusions about ages of human migrations on the basis of Y-STR variance.

European Journal of Human Genetics doi:10.1038/ejhg.2008.249

Y-chromosomal evidence of the cultural diffusion of agriculture in southeast Europe

Vincenza Battaglia et al.

Abstract

The debate concerning the mechanisms underlying the prehistoric spread of farming to Southeast Europe is framed around the opposing roles of population movement and cultural diffusion. To investigate the possible involvement of local people during the transition of agriculture in the Balkans, we analysed patterns of Y-chromosome diversity in 1206 subjects from 17 population samples, mainly from Southeast Europe. Evidence from three Y-chromosome lineages, I-M423, E-V13 and J-M241, make it possible to distinguish between Holocene Mesolithic forager and subsequent Neolithic range expansions from the eastern Sahara and the Near East, respectively. In particular, whereas the Balkan microsatellite variation associated to J-M241 correlates with the Neolithic period, those related to E-V13 and I-M423 Balkan Y chromosomes are consistent with a late Mesolithic time frame. In addition, the low frequency and variance associated to I-M423 and E-V13 in Anatolia and the Middle East, support an European Mesolithic origin of these two clades. Thus, these Balkan Mesolithic foragers with their own autochthonous genetic signatures, were destined to become the earliest to adopt farming, when it was subsequently introduced by a cadre of migrating farmers from the Near East. These initial local converted farmers became the principal agents spreading this economy using maritime leapfrog colonization strategies in the Adriatic and transmitting the Neolithic cultural package to other adjacent Mesolithic populations. The ensuing range expansions of E-V13 and I-M423 parallel in space and time the diffusion of Neolithic Impressed Ware, thereby supporting a case of cultural diffusion using genetic evidence.

Link

Byzantine coins from the time of the sack of Jerusalem

Tourist discovers trove of 1,300-year-old coins in Jerusalem's City of David

A British tourist working in an archaeological dig in Jerusalem on Sunday unearthed a treasure of 264 gold coins from 1,300 ago. Archaeologists called the find "one of the most impressive deposits ever found in the capital."

The coins were found by Nadine Ross, who came to Israel for one month to volunteer at the archaeological site at the City of David. They all carry the portrait of the Roman emperor Heraclius, who ruled the empire between 610 and 641.

On one side of the coins, Heraclius is depicted wearing a uniform while clasping a cross in his right hand. The flipside of the coin also features the sign of the cross. According to archaeological records, these coins were made during the early years of Heraclius' rule, between 610 and 613 - one year before the 614 Persian conquest of Jerusalem.

Such a large cache of coins from one place is unusual, and is usually a sign that they were deliberately hidden away, their secret lost with the death of their owner.

In 630AD, the emperor Heraclius liberated Jerusalem from the Persians and Jews who sacked it it in 614AD. Thus, the owner of the coins, or his descendants, could quite easily have retrieved the hidden treasure, since only ~15 years had passed.

What seems likely is that the owner never lived to claim his property, being one of the ~90,000 victims of the slaughter of 614AD. By the time the Romans liberated Jerusalem the secret of the buried treasure was already lost.

X chromosome diversity in Africans and non-Africans

From the paper:

The ratio of the tMRCA between chromosome X and the autosomes in West Africans, 0.763 ± 0.026, is consistent with the expected 3/4, but it is lower than 3/4 in non-African populations: 0.635 ± 0.024 in North Europeans and 0.613 ± 0.026 in East Asians (Table 2, Supplementary Note and Supplementary Table 2 online).

I am fairly allergic to explanations invoking genetic drift, and I think that both selection and demography might play a role in the observed discrepancy.

Nature Genetics doi:10.1038/ng.303

Accelerated genetic drift on chromosome X during the human dispersal out of Africa

Alon Keinan et al.

Abstract

Comparisons of chromosome X and the autosomes can illuminate differences in the histories of males and females as well as shed light on the forces of natural selection. We compared the patterns of variation in these parts of the genome using two datasets that we assembled for this study that are both genomic in scale. Three independent analyses show that around the time of the dispersal of modern humans out of Africa, chromosome X experienced much more genetic drift than is expected from the pattern on the autosomes. This is not predicted by known episodes of demographic history, and we found no similar patterns associated with the dispersals into East Asia and Europe. We conclude that a sex-biased process that reduced the female effective population size, or an episode of natural selection unusually affecting chromosome X, was associated with the founding of non-African populations.

Link

mtDNA haplogroup L0 in elite Kenyan distance runners

Med Sci Sports Exerc. 2008 Dec 11.

Mitochondrial Haplogroups Associated with Elite Kenyan Athlete Status.

Scott RA, Fuku N, Onywera VO, Boit M, Wilson RH, Tanaka M, H Goodwin W, Pitsiladis YP.

The maternal inheritance of mitochondrial DNA (mtDNA) has enabled construction of detailed phylogenies. Analysis of key polymorphisms from these phylogenies allows mtDNA to be assigned to haplogroups, which have been associated with elite endurance performance. PURPOSE:: To compare the frequencies of mtDNA haplogroups found in elite Kenyan athletes with those in the general Kenyan population. METHODS:: DNA samples were obtained from 221 national level Kenyan athletes (N), 70 international Kenyan athletes (I), and 85 members of the general Kenyan population (C). mtDNA haplogroups were classified by sequencing 340 bases of hypervariable section (HVS I) and by genotyping known restriction sites. Frequency differences between groups were assessed using exact tests of population differentiation. RESULTS:: The haplogroup distribution of national (P = 0.023) and international athletes (P less than 0.001) differed significantly from controls, with international athletes showing a greater proportion of L0 haplogroups (C = 15%, N = 18%, I = 30%) and lower proportion of L3* haplogroups (C = 48%, N = 36%, I = 26%). Although a high number of international athletes originated from the Rift Valley province relative to controls (C = 20%, N = 65%, I = 81%), subjects from this province did not differ in haplogroup distribution from other regions (P = 0.23). Nor did Bantu subjects differ from Nilotic (P = 0.12) despite an overrepresentation of Nilotic languages among the athletes. CONCLUSIONS:: International athletes differed in their mtDNA haplogroup distribution relative to the general Kenyan population. They displayed an excess of L0 haplogroups and a dearth of L3* haplogroups. These findings suggest that mtDNA haplogroups are influential in elite Kenyan distance running, although population stratification cannot be ruled out.

Link

Fallacies of Evolutionary Psychology @ Scientific American

Scientific American has an article on Evolution of the Mind: 4 Fallacies of Psychology. The Coda of the article:

Among Darwin’s lasting legacies is our knowledge that the human mind evolved by some adaptive process. After all, the human brain is even more costly to run than an internal-combustion engine these days, consuming 18 percent of the body’s energy intake while constituting merely 2 percent of its weight. We wouldn’t have such an organ if it hadn’t performed some important adaptive functions in our evolutionary past.

The challenge for evolutionary psychology is to move from this general fact to some evidentially well-supported specifics about the adaptive processes that shaped the mind. But, as we have seen, the evidence needed to substantiate accounts of adaptation in our lineage during the past couple of million years is scarce. And this isn’t the kind of evidence that is likely to materialize; such evidence is lost to us, probably forever. It may be a cold, hard fact that there are many things about the evolution of the human mind that we will never know and about which we can only idly speculate.

Of course, some speculations are worse than others. Those of Pop EP are deeply flawed. We are unlikely ever to learn much about our evolutionary past by slicing our Pleistocene history into discrete adaptive problems, supposing the mind to be partitioned into discrete solutions to those problems, and then supporting those suppositions with pencil-and-paper data. The field of evolutionary psychology will have to do better. Even its very best, however, may never provide us knowledge of why all our complex human psychological characteristics evolved.

I do have a distaste for popular evolutionary psychology, not because I don't think that a lot of human behavior is genetically defined and the result of adaptation (I do), but because the evidence for this adaptation is simply lacking.

We neither know how the brain works, nor how genes influence the way it works. Nor do we have a good quantitative handle on human behavior. Some aspects of it (general intelligence, for example) are better known than others, but a lot of psychology is more akin to opinion than to deep knowledge.

So, it seems that making a convincing case for adaptation in human behavior will remain a difficult problem for some time, and evolutionary psychology must find a way to go beyond hypothesizing towards hypothesis testing. The study of present day human genetic-behavioral variation will be invaluable to that end, although it will require us to overcome the idea of the human mind as more-or-less a finished product of the Paleolithic, and accept the idea of continuing and perhaps intensifying evolution.

El Greco, defender of Byzantine art

Hand-written Note Shows El Greco Defending Byzantine Style In Face Of Western Art

A new investigation could end many of the speculations about the works of El Greco and the man himself. A hand-written annotation to a book, similar to the glosses of Saint Emilianus, found in Spain in a copy of Lives of the most excellent architects, painters and sculptors by Giorgio Vasari, has led Nicos Hadjinicolau, a researcher from the Institute of Mediterranean Studies, to conclude that the artist – contrary to popular belief– was a defender of Byzantine art.

...

Hadjinicolau says there are no other records of the painter’s critical opinion on the art form aside from the hand-written annotation attributed to him. “The passage I have studied is the exception to the rule, the only time that he makes a comment – and a spirited one – against Vasari,” the expert tells SINC.
A literal translation of the note attributed to the painter reads: “If [Vasari] really knew the nature of the Greek style of which he speaks, he would deal with it differently in what he says. He compares it with Giotto, but what Giotto did is simple in comparison, because the Greek style is full of ingenious difficulties.”

Huge Greek necropolis from Himera, Sicily

The discovery of such a large number of burials is a rare opportunity for an ancient DNA study of the Greeks of Sicily. The age of the samples, and the fact that they are from freshly excavated graves will make it relatively easy to extract useful DNA from them. Let's hope that we see some results in the next few years.

Ancient Mass Graves of Soldiers, Babies, Found in Italy

More than 10,000 graves containing ancient amphorae, "baby bottles," and the bodies of soldiers who fought the Carthaginians were found near the ancient Greek colony of Himera, in Italy, archaeologists announced recently.

"It's probably the largest Greek necropolis in Sicily," said Stefano Vassallo, the lead archaeologist of the team that made the discoveries, in September.

The ancient burial ground was uncovered during the construction of a railway extension.

"The remains of Himera's buildings had been known and studied for a long time, and we knew there should be some graves. We didn't expect so many graves", said Vassallo, who works for the Italian province of Palermo's government.

"Each [mass grave] contains from 15 to 25 skeletons. They were all young healthy men and they all died a violent death. Some of the skeletons have broken skulls and in some cases we found the tips of the arrows that killed them," Vassallo said.

He thinks the human remains are from soldiers who died fighting the Carthaginians in a famous 480 B.C. battle described by Greek historian Herodotus of Halicarnassus.

Out of Iberia and into North Africa

American Journal of Physical Anthropology

Post-last glacial maximum expansion from Iberia to North Africa revealed by fine characterization of mtDNA H haplogroup in Tunisia

Lotfi Cherni et al.

Abstract

The first large-scale fine characterization of Tunisian H lineages clarifies that the post-Last glacial maximum expansion originating in Iberia not only led to the resettlement of Europe but also of North Africa. We found that 46% of 81 Tunisian H lineages subscreened for 1,580 bp in mtDNA coding region were affiliated with H1 and H3 subhaplogroups, which are known to have originated in Iberia. Although no signs of local expansion were detected, which would allow a clear dating of their introduction, the younger and less diverse Tunisian H1 and H3 lineages indicate Iberia as the radiating centre. Major contributions from historical migrations to this Iberian genetic imprint in Tunisia were ruled out by the mtDNA gene pool similarity between Berber/Arab/cosmopolitan samples and some "Andalusian" communities, settled by the descendents of the "Moors" who once lived in Iberia for 10 centuries (between 8th and 17th centuries), before being expelled to Tunisia.

Link

Genetic predisposition for fathering sons

A good explanation from BBC News:

Newcastle University researchers found men were more likely to have sons if they had more brothers and vice versa if they had more sisters.

They looked at 927 family trees, with details on 556,387 people from North America and Europe, going back to 1600.

The same link between sibling sex and offspring sex was not found for women.

...

In the years after World War I, there was an upsurge in boy births, and Dr Gellatly said that a genetic shift could explain this.

The odds, he said, would favour fathers with more sons - each carrying the "boy" gene - having a son return from war alive, compared with fathers who had more daughters, who might see their only son killed in action.

However, this would mean that more boys would be fathered in the following generation, he said.

Evolutionary Biology doi:10.1007/s11692-008-9046-3

Trends in Population Sex Ratios May be Explained by Changes in the Frequencies of Polymorphic Alleles of a Sex Ratio Gene

Corry Gellatly

Abstract

A test for heritability of the sex ratio in human genealogical data is reported here, with the finding that there is significant heritability of the parental sex ratio by male, but not female offspring. A population genetic model was used to examine the hypothesis that this is the result of an autosomal gene with polymorphic alleles, which affects the sex ratio of offspring through the male reproductive system. The model simulations show that an equilibrium sex ratio may be maintained by frequency dependent selection acting on the heritable variation provided by the gene. It is also shown that increased mortality of pre-reproductive males causes an increase in male births in following generations, which explains why increases in the sex ratio have been seen after wars, also why higher infant and juvenile mortality of males may be the cause of the male-bias typically seen in the human primary sex ratio. It is concluded that various trends seen in population sex ratios are the result of changes in the relative frequencies of the polymorphic alleles of the proposed gene. It is argued that this occurs by common inheritance and that parental resource expenditure per sex of offspring is not a factor in the heritability of sex ratio variation.

Link

Y chromosomes. mtDNA, and autosomal DNA from Tamil Nadu and Andhra Pradesh

This paper is a winner in my book, if only for this statement:

In addition, the Y-chromosome and mtDNA may both have been affected by natural selection, [46, 47] which can further complicate the interpretation of population history. Coalescence dates based on these systems must also be viewed with appropriate caution, in part because of their large confidence intervals. More importantly, a coalescence date is not necessarily a reliable indicator of the founding date of a population [45] because these dates are affected by the size of the founder population and by subsequent gene flow patterns.

BMC Genetics doi:10.1186/1471-2156-9-86

Genetic variation in South Indian castes: evidence from Y-chromosome, mitochondrial, and autosomal polymorphisms

W. S. Watkins et al.

Abstract (provisional)

Background

Major population movements, social structure, and caste endogamy have influenced the genetic structure of Indian populations. An understanding of these influences is increasingly important as gene mapping and case-control studies are initiated in South Indian populations.

Results

We report new data on 155 individuals from four Tamil caste populations of South India and perform comparative analyses with caste populations from the neighboring state of Andhra Pradesh. Genetic differentiation among Tamil castes is low (RST = 0.96% for 45 autosomal short tandem repeat (STR) markers), reflecting a largely common origin. Nonetheless, caste- and continent-specific patterns are evident. For 32 lineage-defining Y-chromosome SNPs, Tamil castes show higher affinity to Europeans than to eastern Asians, and genetic distance estimates to the Europeans are ordered by caste rank. For 32 lineage-defining mitochondrial SNPs and hypervariable sequence (HVS) 1, Tamil castes have higher affinity to eastern Asians than to Europeans. For 45 autosomal STRs, upper and middle rank castes show higher affinity to Europeans than do lower rank castes from either Tamil Nadu or Andhra Pradesh. Local between-caste variation (Tamil Nadu RST = 0.96%, Andhra Pradesh RST = 0.77%) exceeds the estimate of variation between these geographically separated groups (RST = 0.12%). Low, but statistically significant, correlations between caste rank distance and genetic distance are demonstrated for Tamil castes using Y-chromosome, mtDNA, and autosomal data.

Conclusions

Genetic data from Y-chromosome, mtDNA, and autosomal STRs are in accord with historical accounts of northwest to southeast population movements in India. The influence of ancient and historical population movements and caste social structure can be detected and replicated in South Indian caste populations from two different geographic regions.

Link