Friday, August 31, 2018

Strength of Gravity Measured With New Precision

Increased precision in measuring fundamental physical constants pervasively impacts the accuracy of physics measurements and our capacity to distinguish new physics from existing physics, in general. The new data roughly triple the precision with which Newton's constant, a.k.a. G, has been measured to roughly one part per 86,000.
Two new measurements for the strength of gravity (red squares, with short error bars indicating uncertainty) fall close to or within the currently accepted range for Big G (shaded gray). The new estimates are much more precise than those from other experiments in the last 40 years (teal dots and longer error bars).

The current accepted value for G, based on measurements from the last 40 years, is 6.67408 × 10−11meters cubed per kilogram per square second. That figure is saddled with an uncertainty of 0.0047 percent, making it thousands of times more imprecise than other fundamental constants — unchanging, universal values such as the charge of an electron or the speed of light (SN: 11/12/16, p. 24). The cloud of uncertainty surrounding G limits how well researchers can determine the masses of celestial objects and the values of other constants that are based on G (SN: 4/23/11, p. 28). . . . 
These torsion pendulum experiments yielded G values of 6.674184 × 10−11 and 6.674484 × 10−11 meters cubed per kilogram per square second, both with an uncertainty of about 0.00116 percent.
From Science News. The papers it relied upon were:

Q. Li et al. Measurements of the gravitational constant using two independent methods. Nature. Vol. 560, August 30, 2018, p. 582. doi: 10.1038/s41586-018-0431-5.

S. Schlamminger. Gravity measured with record precision. Nature. Vol. 560, August 30, 2018, p. 562. doi: 10.1038/d41586-018-06028-6.

Of course, other physical constant and coupling constant measurements also continue to become more precise.

Sunday, August 26, 2018

The Hunger Stones And Their Antecedents

This is a notable genre of historically expression that I've only encountered once before, an an inscription from the arid period of ca. 2200 BCE in Mesopotamia that toppled the Akkadian Empire.* 

A lengthy drought in Europe has exposed carved boulders, known as "hunger stones," that have been used for centuries to commemorate historic droughts — and warn of their consequences. 
The Associated Press reports that hunger stones are newly visible in the Elbe River, which begins in the Czech Republic and flows through Germany. 
"Over a dozen of the hunger stones, chosen to record low water levels, can now be seen in and near the northern Czech town of Decin near the German border," the AP writes.

One of the stones on the banks of the Elbe is carved with the words "Wenn du mich siehst, dann weine": "If you see me, weep." 
A team of Czech researchers described that stone in detail in a 2013 paper about the history of droughts in Czech lands. 
The stone is also chiseled with "the years of hardship and the initials of authors lost to history," the researchers wrote:

"It expressed that drought had brought a bad harvest, lack of food, high prices and hunger for poor people. Before 1900, the following droughts are commemorated on the stone: 1417, 1616, 1707, 1746, 1790, 1800, 1811, 1830, 1842, 1868, 1892, and 1893." 
. . .
Tree-ring research in north-central Europe has found evidence of repeated "megadroughts" in the 15th through 19th centuries. 
And an article in Nature earlier this summer compared recent droughts in Europe to droughts over the last 250 years. The scientists found that the 21st century droughts were indeed extreme, but not as long-lasting or as massive as the worst of the historic ones. 
However, the same study noted that the more recent droughts are also linked to record-breaking temperatures. That appears to be causing "unprecedented drying trends" for the soil, which hurts crops. 
This trend "raises concerns about the consequences of extreme meteorological droughts" as the climate continues to warm, the researchers note. 
The drought in northern and central Europe this year is "one of the most intense regional droughts in recent memory," The Guardian wrote in July, and it is paired with abnormally hot temperatures.
From National Public Radio.

The drought of 1790 coincides with the French Revolution. The last several coincide with considerable surges in migration to New World.

* These inscriptions are known as the Curse of Akkad:
For the first time since cities were built and founded, 
The great agricultural tracts produced no grain, 
The inundated tracts produced no fish, 
The irrigated orchards produced neither syrup nor wine, 
The gathered clouds did not rain, the masgurum did not grow. 
At that time, one shekel's worth of oil was only one-half quart, 
One shekel's worth of grain was only one-half quart. . . . 
These sold at such prices in the markets of all the cities! 
He who slept on the roof, died on the roof, 
He who slept in the house, had no burial, 
People were flailing at themselves from hunger.
A more complete version can be found here.

The same drought may also have been responsible for the demise of the Sarasvati River and collapse of Harappan civilization the opened the door for Indo-Europeans to advance into South Asia. The Old Kingdom in Egypt (2686 BCE – 2181 BCE) collapsed around the same time, giving rise to the First Intermediate Period in which the Egyptian empire collapsed into two kingdoms, each with declining central authority after having been united in one, that ended around 2080 BCE. And, this drought may have weakened the states in Anatolia, allowing the first Hittite city-state to establish itself there.

It may even had led to the demise of a civilization in China: "The drought may have caused the collapse of Neolithic Cultures around Central China during the late 3rd millennium BCE. At the same time, the middle reaches of the Yellow River saw a series of extraordinary floods related to the legendary figure of Yu the Great. In the Yishu River Basin, the flourishing Longshan culture was affected by a cooling that severely reduced rice output. This led to substantial decrease in population and fewer archaeological sites. In about 2000 BCE, Longshan was displaced by the Yueshi culture, which had fewer and less sophisticated artifacts of ceramic and bronze."

This drought may be responsible for the prohibitions on pig eating that survive today in Jewish Kosher rules and Islamic halal dietary restrictions according to William J. Burroughs, "Climate Change in Prehistory: The End of the Age of Chaos" (2005). 

A volcanic eruption is one possible explanation for this drought also known as the 4.2 kiloyear climate event, although a 2013 paper fingered an asteroid impact. The 4.2-kiloyear BP aridification event was one of the most severe climatic events of the Holocene period. It defines the beginning of the current Meghalayan age in the Holocene epoch. 

Tuesday, August 21, 2018

Blue Eyes Were Common In The Copper Age Levant

Historical human geneticist Iosif Lazaridis notes on Twitter that:
A huge surprise of the new @EadaoinSays et al. paper on Chalcolithic Levant is that the OCA2/s12913832 "blue eye" allele frequency is ~1/2, i.e., Chalcolithic Levantines were probably more blue-eyed than Bronze Age people from Russia, a complete inversion of what is now observed.
Mass migration clearly played a part, although Levantines were almost surely not a source for Russian and Ukrainian populations based upon other genetic indicators.

More Twitter discussion here. The abstract of the paper based on ancient DNA results explains that:
The material culture of the Late Chalcolithic period in the southern Levant (4500–3900/3800 BCE) is qualitatively distinct from previous and subsequent periods. 
Here, to test the hypothesis that the advent and decline of this culture was influenced by movements of people, we generated genome-wide ancient DNA from 22 individuals from Peqi’in Cave, Israel. These individuals were part of a homogeneous population that can be modeled as deriving ~57% of its ancestry from groups related to those of the local Levant Neolithic, ~17% from groups related to those of the Iran Chalcolithic, and ~26% from groups related to those of the Anatolian Neolithic. 
The Peqi’in population also appears to have contributed differently to later Bronze Age groups, one of which we show cannot plausibly have descended from the same population as that of Peqi’in Cave. These results provide an example of how population movements propelled cultural changes in the deep past.
Modern Peq'in in Israel (near the Lebanese-Israeli border) is predominantly Druze in ethnicity, but are almost surely not descendants of the Chalcolithic residents of the area.

Fathers Pass On Words While Mothers Pass On Sounds?

[R]esearchers, led by population geneticist Li Jin, found that in Indo-European populations, the paternal lineages (Y-chromosome) were correlated to the vocabulary (lexicon) of their languages, meanwhile the maternal lineages were associated with their pronunciations (phoneme).
From here. The paper is:

Menghari Zhang, et al., "Reconciling the father tongue and mother tongue hypotheses in Indo-European populations" National Science Review (2018)

The Thames Valley ca. 125,000 Years Ago

[T]he Thames Valley (now home to London, for example) about 125,000 years ago during the Last Interglacial with hippo, straight-tusked elephant (now extinct), buffalo and hyena, by artist Óscar Sanisidro.

This and more here.

Andean Elevation Adaptations Differ From Tibetan Ones

In Tibet, human hypoxia response was a major evolutionary adaptation to high elevations (probably acquired via introgression from archaic hominins called Denisovans). In the Andean highlands, in contrast, where the potato was domesticated, there are adaptations for starch digestion but not for hypoxia.

The Andean highland people also demonstrate the widely recognized reality that highlands and other inaccessible places tend to be refugia for populations wiped out elsewhere, while lowlands are more vulnerable to population replacement.

The genetic split date between low and high elevation populations in the Andean mountains, however, ca. 7150 BCE to 6150 BCE, is surprisingly recent for a territory that modern humans had very likely colonized by 12000 BCE.
The peopling of the Andean highlands above 2500m in elevation was a complex process that included cultural, biological and genetic adaptations. Here we present a time series of ancient whole genomes from the Andes of Peru, dating back to 7,000 calendar years before present (BP), and compare them to 64 new genome-wide genetic variation datasets from both high and lowland populations. 
We infer three significant features: a split between low and high elevation populations that occurred between 9200-8200 BP; a population collapse after European contact that is significantly more severe in South American lowlanders than in highland populations; and evidence for positive selection at genetic loci related to starch digestion and plausibly pathogen resistance after European contact
Importantly, we do not find selective sweep signals related to known components of the human hypoxia response, which may suggest more complex modes of genetic adaptation to high altitude.
John Lindo, et al., "The genetic prehistory of the Andean highlands 7,000 Years BP though European contact" bioRxiv (July 31, 2018).

Can GR Really Be Reasonably Approximated With Newtonian Dynamics In Galaxies?

Newtonian v. post-Newtonian Analysis of Galaxy Scale Physics

It is common practice in N-body simulations of gravity in galaxies to assume that the relativistic effects that distinguish General Relativity from Newtonian gravity are negligible and to use Newtonian gravity as a result.

But, a tool called post-Newtonian theory, which approximates the non-Newtonian effects of General Relativity by perturbing Newtonian gravitational expectations with Post-Newtonian terms, has been applied in a recent paper to suggest that maybe those post-Newtonian effects aren't so negligible after all. Basically, post-Newtonian theory approximates a lot of the discrepancy between Newtonian gravity and General Relativity, but not all of it.

This is particularly notable because post-Newtonian theory has consistently punched above its weight class, (see, e.g. here and here) showing fewer discrepancies between this perturbative approximation and either full fledge General Relativity from first principles or experimental observations than a naive theoretical error estimate would suggest.

The paper is as follows:
The gravitational stability of a two-dimensional self-gravitating and differentially rotating gaseous disk in the context of post-Newtonian (hereafter PN) theory is studied. Using the perturbative method and applying the second iterated equations of PN approximation, the relativistic version of the dispersion relation for the propagation of small perturbations is found. We obtain the PN version of Toomre's local stability criterion by utilizing this PN dispersion relation. In other words, we find relativistic corrections to Toomre's criterion in the first PN approximation. 
Two stability parameters η and μ related to gravity and pressure are introduced. We illustrate how these parameters determine the stability of the Newtonian and PN systems. Moreover, we show that, in general, the differentially rotating fluid disk is more stable in the context of PN theory relative to the Newtonian one. Also, we explicitly show that although the relativistic PN corrections destabilize non-rotating systems, they have the stabilizing role in the rotating thin disks. Finally, we apply the results to the relativistic disks around hypermassive neutron stars (HMNSs), and find that although Newtonian description predicts the occurrence of local fragmentations, PN theory remains in agreement with the relevant simulations, and rules out the existence of local fragmentations.
Ali Kazemi, Mahmood Roshan, Elham Nazari "Post-Newtonian corrections to Toomre's criterion" (August 17, 2018) (accepted in ApJ).

Previous papers by overlapping authors include a paper exploring topics similar to this one, and a post-Newtonian Jeans analysis.

Modified Gravity and post-Newtonian Theory

One of the authors has a paper looking at the emergence of stellar bars in Moffat's MOG theory. MOG and PN both induce stability in disk galaxies relative to Newtonian approximations in a paper from earlier this year:
We study the stellar bar growth in high resolution numerical galaxy models with and without dark matter halos. In all models the galactic disk is exponential and the halos are rigid or live Plummer spheres. More specifically, when there is no dark matter halo, we modify the gravitational force between point particles. To do so we use the weak field limit of an alternative theory of dark matter known as MOG in the literature. The galaxy model in MOG has the same initial conditions as in galaxy models with dark matter halo. On the other hand, the initial random velocities and the Toomre's local stability parameter are the same for all the models. 
We show that the evolution and growth of the bar in MOG is substantially different from the standard cases including dark matter halo. More importantly, we find that the bar growth rate and its final magnitude is smaller in MOG. On the other hand, the maximum value of the bar in MOG is smaller than the Newtonian models. It is shown that although the live dark matter halo may support the bar instability, MOG has stabilizing effects. Furthermore, we show that MOG supports fast pattern speeds, and unlike in the dark matter halo models pattern speed does not decrease with time. Theses differences, combined with the relevant observations, may help to distinguish between dark matter an modified gravity in galactic scales.

Mahmood Roshan, "Stellar Bar evolution in the absence of dark matter halo" (January 25, 2018).

Another MOG study with overlapping authorship is here.

MOG is more elaborate than MOND, but is relativistic and consistently performs well in areas like CBM predictions and galactic clusters, where the toy model theory of MOND does not.

How Accurately Can Scalar Graviton Theories Reproduce GR and Observations?

The classical Post-Newtonian scheme has some similarities to that of Deur's quantum gravity efforts which is a quantum static massless scalar graviton approximation to true quantum gravity, arranged the terms of his quantum gravity equation so that the first term is equivalent to Newtonian gravity, and the next two or three higher order terms give rise to quantum gravity effects that produce dark matter and dark energy phenomena. In this case, scalar gravitons are used merely as an approximation that is easier to calculate with and not because the theory presumes that real gravitons are spin-0 rather than spin-2.

Another comparison of post-Newtonian theory to scalar graviton models that consider self-interaction in light of the PPN (parameterize post-Newtonian) formalism can be found here:
We construct a general stratified scalar theory of gravitation from a field equation that accounts for the self-interaction of the field and a particle Lagrangian, and calculate its post-Newtonian parameters. Using this general framework, we analyze several specific scalar theories of gravitation and check their predictions for the solar system post-Newtonian effects.
Diogo P. L. Bragança, José P. S. Lemos "Stratified scalar field theories of gravitation with self-energy term and effective particle Lagrangian" (June 29, 2018).

The conclusion to this paper notes that:
In this paper, we presented a general stratified scalar field theory of gravitation in a Minkowski background. Then, we calculated two post-Newtonian parameters from three general parameters of the theory B, C and k, concluding that it is perfectly possible for such a scalar theory to explain the four solar system tests. Finally, we used this general theory to rapidly compute the PPN parameters β and γ for a set of scalar theories of gravitation to verify if they agree with the experimental tests of gravitation in the solar system. Therefore, with this formalism, one can directly find those two PPN parameters only from the field equation and the particle Lagrangian of a given scalar theory of gravitation. Although this is a very efficient method to calculate β and γ for a given theory, it does not allow one to compute the other PPN parameters. It would be interesting to generalize this approach to efficiently calculate the remaining PPN parameters for scalar theories and verify if it is possible for such a theory to explain every phenomenon predicted by general relativity. 
The stratified theories that were analyzed (Page and Tupper’s, and Ni’s) yielded the correct PPN parameters relevant for solar system tests. One could wonder whether this indicates that they are valid theories, and the answer to that relies in analyzing the remaining PPN parameters. This analysis was done by Nordtvedt and Will [60] and Ni [50] and the conclusion was that stratified theories cannot account for Earth-tide measurements due to the motion of the solar system relative to the preferred frame (defined by the distant stars). 
The conformal theories that were analyzed did not yield the correct γ parameter even in very general cases. This motivates future work on the analysis of a relativistic scalar theory including a derivative coupling in the Lagrangian, of the type T ab(∂aΦ)(∂bΦ). Such a theory would not have preferred frame effects (it would respect Lorentz symmetries), so if it predicted the correct parameters β and γ it would not have the problem of Earth-tide measurements. 
If such a scalar theory correctly predicts the outcome of every weak field gravity experiment, then we can only rule it out using strong gravity experiment results (e.g. LIGO, neutron star binaries, cosmology). Note also that a scalar theory of gravity is much simpler than general relativity, since it describes gravity with one function instead of ten. In such theories, unlike general relativity, it is generally possible to define a local gravitational energy-momentum tensor, which is always an attractive feature, and is still a problem in general relativity.

Sunday, August 19, 2018

A Schwarzschild Radius Heuristic

 is the formula for computing in terms of any speed the distance at which the escape velocity is that speed in Newtonian physics. It is also true that for a Schwarzschild black hole, 

Tuesday, August 14, 2018

Sparrows Co-Evolved With Human Agriculture To Digest Grains More Efficiently

In an ideal world, more papers on subjects like the emergence of agriculture would incorporate corroborating data points like this one that make the narrative robust and more rich.
House sparrows (Passer domesticus) are a hugely successful anthrodependent species; occurring on nearly every continent. Yet, despite their ubiquity and familiarity to humans, surprisingly little is known about their origins. We sought to investigate the evolutionary history of the house sparrow and identify the processes involved in its transition to a human-commensal niche. 
We used a whole genome resequencing dataset of 120 individuals from three Eurasian species, including three populations of Bactrianus sparrows, a non-commensal, divergent house sparrow lineage occurring in the Near East. 
Coalescent modelling supports a split between house and Bactrianus sparrow 11 Kya and an expansion in the house sparrow at 6 Kya, consistent with the spread of agriculture following the Neolithic revolution. Commensal house sparrows therefore likely moved into Europe with the spread of agriculture following this period. Using the Bactrianus sparrow as a proxy for a pre-commensal, ancestral house population, we performed a comparative genome scan to identify genes potentially involved with adaptation to an anthropogenic niche. We identified potential signatures of recent, positive selection in the genome of the commensal house sparrow that are absent in Bactrianus populations. The strongest selected region encompasses two major candidate genes; COL11A—which regulates craniofacial and skull development and AMY2A, part of the amylase gene family which has previously been linked to adaptation to high-starch diets in humans and dogs. Our work examines human-commensalism in an evolutionary framework, identifies genomic regions likely involved in rapid adaptation to this new niche and ties the evolution of this species to the development of modern human civilization.
Mark Ravinet,, et al., "Signatures of human-commensalism in the house sparrow genome" Proceedings of the Royal Society B (August 8, 2018) via this tweet (hat tip Razib Khan).

Unsurprising But Concerning

We find that at least 31.2% of the citations to retracted articles happen a year after the article has been retracted. And that 91.4% of these post-retraction citations are approving.
From here (hat tip Marginal Revolution).

Contemporary Genetics in Singapore Confirm Paradigms

A new paper predictably sees the three main ethnicities of Singapore (Chinese, Malay and Indian), with some admixture between these populations (with the Chinese and Indian populations arriving in the historic era as immigrants). The Malay component of ancestry is absent in the 1000 Genomes Project data. There are also genetic signatures of a separate mainland route Neolithic Austroasiatic wave of migration from South China (ca. 4000 years ago), and an island base Austronesian wave of migration from South China (ca. 2000 years ago).

Asian populations are currently underrepresented in human genetics research. Here we present whole-genome sequencing data of 4,810 Singaporeans from three diverse ethnic groups: 2,780 Chinese, 903 Malays, and 1,127 Indians. 
Despite a medium depth of 13.7X, we achieved essentially perfect (>99.8%) sensitivity and accuracy for detecting common variants and good sensitivity (>89%) for detecting extremely rare variants with <0.1% allele frequency. We found 89.2 million single-nucleotide polymorphisms (SNPs) and 9.1 million small insertions and deletions (INDELs), more than half of which have not been cataloged in dbSNP. In particular, we found 126 common deleterious mutations (MAF>0.01) that were absent in the existing public databases, highlighting the importance of local population reference for genetic diagnosis. 
We describe fine-scale genetic structure of Singapore populations and their relationship to worldwide populations from the 1000 Genomes Project. In addition to revealing noticeable amounts of admixture among three Singapore populations and a Malay-related novel ancestry component that has not been captured by the 1000 Genomes Project, our analysis also identified some fine-scale features of genetic structure consistent with two waves of prehistoric migration from south China to Southeast Asia. Finally, we demonstrate that our data can substantially improve genotype imputation not only for Singapore populations, but also for populations across Asia and Oceania. These results highlight the genetic diversity in Singapore and the potential impacts of our data as a resource to empower human genetics discovery in a broad geographic region.

The juicy bit of the discussion section reads as follows:
Malay represents indigenous people in Southeast Asia and contributes a novel ancestry component that was not captured by the 1000 Genomes Project. We observed a clear north-south clinal pattern of genetic variation in both South Asia and East/Southeast Asia, except for two recent migrant populations--the SG Chinese and SG Indian, which is consistent with previous studies that suggest a strong role of geography in producing human population structure. 
Moreover, we found noticeable amounts of admixture among the three major populations in Singapore. 
In addition, we identified two closely related ancestral components (components 4 and 5 in Figure 2E) that are prevalent in East and Southeast Asian populations, suggestive of their ancient origins. Based on the geographic distributions of these two components, we speculate that they might reflect two waves of prehistoric migration from south China to Southeast Asia through a mainland route (component 5) and an island route (component 4). This hypothesis is consistent with a complex peopling history of Southeast Asia depicted by a recent ancient DNA study. The study suggested that an expansion from East Asia into mainland Southeast Asia occurred about 4,000 years ago during the Neolithic transition to farming, and that an island route migration corresponding to the Austronesian expansion into Philippines and Indonesia took place about 2,000 years ago. 
So, the new study adds a few, basically unsurprising, but important, data points to the mix, but provides no big surprises or insights. 

Wednesday, August 8, 2018

Contemporary Corsican Y-DNA Sheds Light On Southern European Pre-History

Historical Background

Bernard's blog provides a capsule history of Corsica and then explores a new paper on its genetics:
The most widely accepted hypothesis is the colonization of the Corsican-Sardinian bloc from Tuscany during different ice ages. Thus the first colonization of Corsica can go back to the Mesolithic between 18,000 and 15,000 years. The oldest archeological evidence is the Mesolithic collective burial of Campo Stefano located in the south of Corsica. It is 8940 years old. Other Mesolithic sites are identified in the south-west Filitosa and southern Corsica, as well as in Sardinia. 
A major demographic change occurred in the Neolithic from the sixth millennium BC. The archaeological remains are carved stones and pottery of printed ceramics, cardial or Campaniform. 
The Corsican prehistory ends when the Greeks settle on the island building the city of Alalia in 565 BC. JC. The Greeks were followed by Romans, Vandals and Byzantines.
There were also early Iron Age Greek colonies in Italy and Southern France before the full ascendancy of the Western Roman Empire.

The genetic data recounted below suggests that the Romans, and even less so, the Vandals and Byzantines didn't appear to have had much of a demic impact on Corsica. Corsica was eventually claimed by France, the country which controls it today, and the demic impact of subsequent Northern Italian and French rulers also appears to have been modest, although broad similarities between Northern Italy, Southern France and Corsica could obscure these sources of admixture.
After being ruled by the Republic of Genoa since 1284, Corsica was briefly an independent Corsican Republic from 1755 until it was officially ceded by the Republic of Genoa to Louis XV as part of a pledge for debts in 1768. Due to Corsica's historical ties with the Italian peninsula, the island retains to this day many Italian cultural elements: the native tongue is recognised as a regional language by the French government. Corsica was ruled by various powers over the course of its history, but had several brief periods of self-government. 
Napoleon was born in 1769 in the Corsican capital of Ajaccio. His ancestral home, Maison Bonaparte, is today a significant visitor attraction and museum.
The Genetics of Corsica and its Vicinity

Bernard summarizes the findings of a new genetics paper on Corsica as follow:
Y chromosome DNA in Corsica shows several waves of populations. The oldest is characterized by the arrival of haplogroup I2 in the Mesolithic. Deep demographic changes in the Neolithic are identified by the presence of haplogroup G. The Copper Age sees the arrival of haplogroup R on the island. The difference in distribution of the two subclades R1b-U152 and R1b-U106 may correspond to the two groups of statue-menhirs erected in the Bronze Age and distributed to the north and south. The settlement of the Greek city of Alaria seems to correspond to the maximum frequency of haplogroup E1b-V13. 
Regarding relations between Corsica and Sardinia, the results of this study suggest two different genetic histories, Nuragic and Torréenne . The distribution of haplogroup G also suggests a continuity between southern Corsica and Sardinia, while that of haplogroup I suggests a distinction. Indeed the Corso-Sardinian block is characterized by a climatic contrast. The glacial sediments in northern Corsica suggest three glacial episodes, whereas these sediments are absent in Sardinia. It is reasonable to think that the first Mesolithic arrived in Sardinia, where the climate is more favorable, before joining Corsica when the temperature has softened.
From Bernard's blog via Google translate from French (emphasis and link re Alaria added) discussing Julie Di Cristofaro, et al., Prehistoric migrations through the Mediterranean basin shaped Corsican Y-chromosome diversity PLOS (2018). 

I largely concur with Bernard's analysis above, although the estimated date of Y-DNA R's arrival may be a bit early for what could have been an early Bronze Age arrival instead.

Some of the interesting points in the raw data pertain to Y-DNA in Provence and Tuscany which are used for comparison purposes (I've interlineated editorial commentary in brackets and added emphasis to some of Bernard's translated blog text. I've also made some minor translation corrections.)
Haplogroup R is the most common in Corsica with a value of 51.8%. This haplogroup reaches 90% in Provence and 45.3% in Tuscany. The subclade R1b-U152 is predominant, especially in North Corsica. Nevertheless the subclade R1b-U106 is present in South Corsica. In Europe, R1b-U152 is the most common in Switzerland, Italy, France and Western Poland. Early DNA studies have shown that haplogroup R has spread in Western Europe in the Copper Age and the Bronze Age. 
Haplogroup G has a frequency of 21.7% in Corsica and 13.3% in Tuscany. It is absent in Provence. The subclade G2a-L91 reaches 11.3% in Corsica and is absent in Tuscany. G2a-L91 and G2a-PF3147 reach their highest frequency in Sardinia and Southern Corsica. Early DNA studies have shown that haplogroup G spread in Europe with Neolithic farmers. 
Haplogroup J shows an intermediate frequency in Corsica (11.8%) between those of Provence (6.6%) and Tuscany (17.6%). The subclade J2a-M67 is homogeneous on the island with a TMRCA of 2380 years. [Ed. i.e. 430 B.C.E., which is in the early Iron Age.] Subclade J2a-Page55 is present in northwestern Corsica. 
Haplogroup E is mainly represented by its subclade E1b-V13. Its frequency in Corsica (5.5%) is intermediate between those of Provence  (3%) and Tuscany (10.4%). The diffusion of E1b-V13 is supposed to be related to the Neolithic expansion.  [Ed. E1b-V13, which is my Y-DNA clade, is the predominant Y-DNA E clade in Europe and probably arrived via Greece and the Balkans.]
Haplogroup I is present in Corsica under its two clades I1 (0.3%) and I2 (2.4%). It is absent in Provence and present in Tuscany: I1 (0.3%) and I2 (6.3%). Clade I1 is mainly present in Northern Europe [Ed. with a Neolithic era expansion.], while clade I2 is mainly divided into two subclades: I2-P37 and I2-M436. The latter is present mainly in the Balkans. Ancient DNA studies have shown us that I2 is associated with the Mesolithic in Europe. It is also present in the Neolithic especially in the south of France. The subclade I2-M26 found in 30% of the samples in Sardinia is very little present in Corsica. 
Haplogroup Q is present in Corsica with a frequency of 2.4%. He is absent in Provence and has a frequency of 0.6% in Tuscany. [Ed. A frequency of Y-DNA Q that high in Corsica is probably a founder effect. Y-DNA Q is quite rare in Europe.]
Bernard doesn't discuss the distribution of Y-DNA T-M70 which was also present, but this would appear to be a good candidate for a Cardial Pottery Neolithic source, based upon its distribution within Corsica and where Y-DNA T is found elsewhere.

The Y-DNA R1b-U152 distribution probably implies a Bell Beaker related source in these areas, which is notable as I had been unclear on the extent of Y-DNA R1b distributions in Switzerland, Southern France and Northern Italy (I admit that I had never really even wondered about its presence in Corsica).

As far back as attested history goes, Northern Italy was Italic (probably due to early Iron Age migrations) with an intrusive Etruscan migration as well in that time period. The earliest attested linguistic data for Southern France was that it was ruled by Celtic tribes, although there may have been Vasconic speakers in the far Southwest.

Bernard and I both think that Greek colonization in the early Iron Age is a more likely source of Y-DNA E1b-V13 in these populations than Neolithic era expansions something that also fits the relative frequencies in Provence and Tuscany. Y-DNA J and E1b-V13 likely arrived at around the same time., even though Y-DNA J is more widely distributed in Corsica than Y-DNA E1b-V13. This Greek colonization event could also be the source of some of the Y-DNA I2 in the sample.

Inferred Dark Matter Distributions In Galaxy Clusters Also Track Baryonic Matter

We study the total and dark matter (DM) density profiles as well as their correlations for a sample of 15 high-mass galaxy clusters by extending our previous work on several clusters from Newman et al. Our analysis focuses on 15 CLASH X-ray-selected clusters that have high-quality weak- and strong-lensing measurements from combined Subaru and Hubble Space Telescope observations. The total density profiles derived from lensing are interpreted based on the two-phase scenario of cluster formation. 
In this context, the brightest cluster galaxy (BCG) forms in the first dissipative phase, followed by a dissipationless phase where baryonic physics flattens the inner DM distribution. This results in the formation of clusters with modified DM distribution and several correlations between characteristic quantities of the clusters. 
We find that the central DM density profiles of the clusters are strongly influenced by baryonic physics as found in our earlier work. The inner slope of the DM density for the CLASH clusters is found to be flatter than the Navarro--Frenk--White profile, ranging from α=0.30 to 0.79. We examine correlations of the DM density slope α with the effective radius Re and stellar mass Me of the BCG, finding that these quantities are anti-correlated with a Spearman correlation coefficient of 0.6. We also study the correlation between Re and the cluster halo mass M500, and the correlation between the total masses inside 5 kpc and 100 kpc. We find that these quantities are correlated with Spearman coefficients of 0.68 and 0.64, respectively. These observed correlations are in support of the physical picture proposed by Newman et al.

This is not a smoking gun for any theory, but it reaffirmed the lesson of inferred dark matter distributions in galaxies that inferred dark matter distributions closely track the distribution of ordinary baryonic matter there. This means that the an appropriate modified gravity theory can probably also explain the dark matter phenomena of clusters, even though the simply toy model formula of MOND is not adequate to do so.

The failure to the NFW distribution of dark matter in clusters as well as has been previously shown, in galaxies, also strongly supports the conclusion that if there are indeed dark matter particles, that they interact with ordinary matter more strongly than by gravity alone, and hence, dark matter cannot be truly collisionless.

As an aside, some of these authors were also authors of a recent paper claiming that the data do not disclose a fundamental acceleration scale, which is simply shoddy work (see critiques spelling out the flaws in their analysis here and here). So a grain of salt may be required when looking at their data analysis and conclusions.

On the other hand, a 2017 paper by many of the same authors confirms as other have found that the NFW inferred dark matter halo shape is a poor fit to more than 75% of galaxies and an indifferent fit to the remainder, even in large galaxies where the usual justifications for deviations from the NFW shaped halo expected for collisionless dark matter are weaker.  Its abstract is as follows, emphasis added:
We develop and apply new techniques in order to uncover galaxy rotation curves (RC) systematics. Considering that an ideal dark matter (DM) profile should yield RCs that have no bias towards any particular radius, we find that the Burkert DM profile satisfies the test, while the Navarro-Frenk-While (NFW) profile has a tendency of better fitting the region between one and two disc scale lengths than the inner disc scale length region. Our sample indicates that this behaviour happens to more than 75% of the galaxies fitted with an NFW halo. Also, this tendency does not weaken by considering "large" galaxies, for instance those with M1010M. Besides the tests on the homogeneity of the fits, we also use a sample of 62 galaxies of diverse types to perform tests on the quality of the overall fit of each galaxy, and to search for correlations with stellar mass, gas mass and the disc scale length. In particular, we find that only 13 galaxies are better fitted by the NFW halo; and that even for the galaxies with M1010M the Burkert profile either fits as good as, or better than, the NFW profile. This result is relevant since different baryonic effects important for the smaller galaxies, like supernova feedback and dynamical friction from baryonic clumps, indicate that at such large stellar masses the NFW profile should be preferred over the Burkert profile. Hence, our results either suggest a new baryonic effect or a change of the dark matter physics.
A 2016 paper by one of the authors and a co-author summarizes the small scale issue of LambadCDM:
The ΛCDM model, or concordance cosmology, as it is often called, is a paradigm at its maturity. It is clearly able to describe the universe at large scale, even if some issues remain open, such as the cosmological constant problem , the small-scale problems in galaxy formation, or the unexplained anomalies in the CMB. ΛCDM clearly shows difficulty at small scales, which could be related to our scant understanding, from the nature of dark matter to that of gravity; or to the role of baryon physics, which is not well understood and implemented in simulation codes or in semi-analytic models. At this stage, it is of fundamental importance to understand whether the problems encountered by the ΛDCM model are a sign of its limits or a sign of our failures in getting the finer details right. In the present paper, we will review the small-scale problems of the ΛCDM model, and we will discuss the proposed solutions and to what extent they are able to give us a theory accurately describing the phenomena in the complete range of scale of the observed universe.