Razib Khan One-stop-shopping for all of my content

September 7, 2012

Across the sea of grass: how Northern Europeans got to be ~10% Northeast Asian

The Pith: You’re Asian. Yes, you!

A conclusion to an important paper, Nick Patterson, Priya Moorjani, Yontao Luo, Swapan Mallick, Nadin Rohland, Yiping Zhan, Teri Genschoreck, Teresa Webster, and David Reich:

In particular, we have presented evidence suggesting that the genetic history of Europe from around 5000 B.C. includes:

1. The arrival of Neolithic farmers probably from the Middle East.

2. Nearly complete replacement of the indigenous Mesolithic southern European populations by Neolithic migrants, and admixture between the Neolithic farmers and the indigenous Europeans in the north.

3. Substantial population movement into Spain occurring around the same time as the archaeologically attested Bell-Beaker phenomenon (HARRISON, 1980).

4. Subsequent mating between peoples of neighboring regions, resulting in isolation-by-distance (LAO et al., 2008; NOVEMBRE et al., 2008). This tended to smooth out population structure that existed 4,000 years ago.

Further, the populations of Sardinia and the Basque country today have been substantially less influenced by these events.

 

It’s in Genetics, Ancient Admixture in Human History. Reading through it I can see why it wasn’t published in Nature or Science: methods are of the essence. The authors review five population genetic statistics of phylogenetic and evolutionary genetic import, before moving onto the novel results. ...

June 28, 2012

Population replacement in Neolithic Spain?

Filed under: Agriculture,Anthroplogy,Neolithic,Paleolithic Europeans — Razib Khan @ 12:16 pm

There’s a new ancient DNA paper out which examines the maternal lineage and the autosomal background of two individuals extracted from a Spanish site dated to 7,000 years before the present. That is, during the European Mesolithic. In other words, these are the last wave of Iberian hunter-gatherers before agriculture. I have placed the PCA, with some informative labels, to illustrate the peculiarity of these samples. Here’s the abstract:

The genetic background of the European Mesolithic and the extent of population replacement during the Neolithic…is poorly understood, both due to the scarcity of human remains from that period…The mitochondria of both individuals are assigned to U5b2c1, a haplotype common among the small number of other previously studied Mesolithic individuals from Northern and Central Europe. This suggests a remarkable genetic uniformity and little phylogeographic structure over a large geographic area of the pre-Neolithic populations. Using Approximate Bayesian Computation, a model of genetic continuity from Mesolithic to Neolithic populations is poorly supported. Furthermore, analyses of 1.34% and 0.53% of their nuclear genomes, containing about 50,000 and 20,000 ancestry informative SNPs, respectively, show that these two Mesolithic individuals are ...

July 30, 2011

A world full of children

Filed under: Agriculture,Culture,Environment,Neolithic,Neolithic Revolution — Razib Khan @ 11:07 pm

The figure to the left is from a new paper in Science, When the World’s Population Took Off: The Springboard of the Neolithic Demographic Transition. It reports the findings from 133 cemeteries in the northern hemisphere in regards to the proportion of 5-19 year old individuals. When calibrated to period when agriculture was introduced into a specific region there seems to be a clear alignment in terms of a demographic transition toward a “youth bulge.” Why? A standard model of land surplus explains part of it surely. When farmers settle “virgin land” there is often a rapid “catch up” phase toward the Malthusian limit, the carrying capacity. Another possibility though is that sedentary populations did not need to space their offspring nearly as much as mobile hunter-gatherers. Whatever the details, the facts remain that the data do point to a shift in the age pyramid during this period. The author wonders as to the possible cultural implications of this. There is an a priori assumption that a young vs. old age profile in a society constrains its choices and channels its energies (e.g., think the “baby boom” generation in ...

July 7, 2011

The biocultural frog and tortoise

As many of you know when you have two adjacent demes, breeding populations, they often rapidly equilibrate in gene frequencies if they were originally distinct. There are plenty of good concrete examples of this. The Hui of China are Muslims who speak local Chinese dialects. The most probable root of this community goes back to the enormous population of Central Asia Muslims brought by the Mongol Yuan dynasty that ruled ruled China for over a century from the late 1200s to 1300s. Genetic studies of this group that I’ve seen indicate that a high bound estimate for West Eurasian ancestry is ~10%. The other ~90% is interchangeable with the Han Chinese. So let’s assume that the Hui are ~10% West Asian. If you assume that in the year 1400 the Hui were “pure,” you have 24 generations (25 years per generation). The original population of “Central Asian Muslims” were heterogeneous, including Iranians and Turks. But let’s take it granted that they were 50% East Eurasian and 50% West Eurasian in ancestry at the time of their arrival. What would the intermarriage rate per generation have to be so ...

June 28, 2011

“What if you’re wrong” – haplogroup J

Back when this sort of thing was cutting edge mtDNA haplogroup J was a pretty big deal. This was the haplogroup often associated with the demic diffusion of Middle Eastern farmers into Europe. This was the “Jasmine” clade in Seven Daughters of Eve. A new paper in PLoS ONE makes an audacious claim: that J is not a lineage which underwent recent demographic expansion, but rather one which has been subject to a specific set of evolutionary dynamics which have skewed the interpretations due to a false “molecular clock” assumption. By this assumption, I mean that mtDNA, which is passed down in an unbroken chain from mother to daughter, is by and large neutral to forces like natural selection and subject to a constant mutational rate which can serve as a calibration clock to the last common ancestor between two different lineages. Additionally, mtDNA has a high mutational rate, so it accumulates lots of variation to sample, and, it is copious, so easy to extract. What’s not to like?

First, the paper, Mutation Rate Switch inside Eurasian Mitochondrial Haplogroups: Impact of Selection and Consequences for Dating Settlement in Europe:

R-lineage mitochondrial DNA represents over 90% of the European ...

June 27, 2011

First Farmers Facing the Ocean

The image above is adapted from the 2010 paper A Predominantly Neolithic Origin for European Paternal Lineages, and it shows the frequencies of Y chromosomal haplogroup R1b1b2 across Europe. As you can see as you approach the Atlantic the frequency converges upon ~100%. Interestingly the fraction of R1b1b2 is highest among populations such as the Basque and the Welsh. This was taken by some researchers in the late 1990s and early 2000s as evidence that the Welsh adopted a Celtic language, prior to which they spoke a dialect distantly related to Basque. Additionally, the assumption was that the Basques were the ur-Europeans. Descendants of the Paleolithic populations of the continent both biologically and culturally, so that the peculiar aspects of the Basque language were attributed by some to its ancient Stone Age origins.

As indicated by the title the above paper overturned such assumptions, and rather implied that the origin of R1b1b2 haplogroup was in the Near East, and associated with the expansion of Middle Eastern farmers from the eastern Mediterranean toward western Europe ~10,000 years ago. Instead of the high frequency of R1b1b2 being a confident peg for the ...

May 31, 2011

Mediterranean men on the move

ResearchBlogging.orgSeriously, sometimes history matches fiction a lot more than we’d have expected, or wished. In the early 2000s the Oxford geneticist Bryan Sykes observed a pattern of discordance between the spatial distribution of male mediated ancestry on the nonrecombinant Y chromosome (NRY) and female mediated ancestry in the mitochondrial DNA (mtDNA). To explains this he offered a somewhat sensationalist narrative to the press about possible repeated instances of male genocide against lineage groups who lost in conflicts.

Here is a portion of the book of Numbers in the Bible:

15 – And Moses said unto them, Have ye saved all the women alive?

16 – Behold, these caused the children of Israel, through the counsel of Balaam, to commit trespass against the LORD in the matter of Peor, and there was a plague among the congregation of the LORD.

17 – Now therefore kill every male among the little ones, and kill every woman that hath known man by lying with him.

18 – But all the women children, that have not known a man by lying with him, keep alive for yourselves.

Then there is the rape of the Sabine women. The ethnogenesis of the mestizo and mulatto populations of ...

May 16, 2011

The genetic complexity of prehistoric Sweden

Thanks to the fact that northern Europe is cool and archaeological research is rather well developed in the region due to quirks of history, there are lots of findings from ancient DNA which are answering long-standing questions. In particular Scandinavia is of special interest in regards to the transition of Europeans from a hunter-gatherer lifestyle to an agricultural one. We know that hunting and gathering as dominant modes of economic production persisted relatively late in European history in this region, up to ~5,000 years before the present. From my cursory reading of the material on the spread of agriculture in northern Europe one dynamic which seems clear is that the rate of expansion was not always constant, and that at the northern fringes in particular social or ecological frontiers served to demarcate the limits to the expansion of farming groups, which often originated from the south and east. Additionally, on the maritime fringes of the North Sea and Baltic there seem to have been relatively dense agglomerations of hunter-gatherers which resisted or coexisted with farming populations for long periods of time (perhaps they were more accurately termed fisher-gatherers!).

This is where Anna Linderholm’s research comes into the picture. I’ve ...

May 4, 2011

2,000 years of Yayoi – Japanese are gaikokujin!

Filed under: Anthroplogy,Culture,Demic Diffusion,Farming,Japan,Neolithic,Yayoi — Razib Khan @ 10:49 pm

A new paper in Proceedings of the Royal Society dovetails with some posts I’ve put up on the peopling of Japan of late. The paper is Bayesian phylogenetic analysis supports an agricultural origin of Japonic languages:

Languages, like genes, evolve by a process of descent with modification. This striking similarity between biological and linguistic evolution allows us to apply phylogenetic methods to explore how languages, as well as the people who speak them, are related to one another through evolutionary history. Language phylogenies constructed with lexical data have so far revealed population expansions of Austronesian, Indo-European and Bantu speakers. However, how robustly a phylogenetic approach can chart the history of language evolution and what language phylogenies reveal about human prehistory must be investigated more thoroughly on a global scale. Here we report a phylogeny of 59 Japonic languages and dialects. We used this phylogeny to estimate time depth of its root and compared it with the time suggested by an agricultural expansion scenario for Japanese origin. In agreement with the scenario, our results indicate that Japonic languages descended from a common ancestor approximately 2182 years ago. Together with archaeological and biological evidence, our results suggest that the first farmers ...

December 13, 2010

Live not by visualization alone

pc1
Synthetic map

In the age of 500,000 SNP studies of genetic variation across dozens of populations obviously we’re a bit beyond lists of ABO blood frequencies. There’s no real way that a conventional human is going to be able to discern patterns of correlated allele frequency variations which point to between population genetic differences on this scale of marker density. So you rely on techniques which extract the general patterns out of the data, and present them to you in a human-comprehensible format. But, there’s an unfortunate tendency for humans to imbue the products of technique with a particular authority which they always should not have.

ResearchBlogging.orgThe History and Geography of Human Genes is arguably the most important historical genetics work of the past generation. It has surely influenced many within the field of genetics, and because of its voluminous elegant visual displays of genetic data it is also a primary source for those outside of genetics to make sense of phylogenetic relations between human populations. And yet one aspect of this great work which never caught on was the utilization of “synthetic maps” to visualize components of genetic variation between populations. This may have been fortuitous, a few years ago a paper was published, Interpreting principal components analyses of spatial population genetic variation, which suggested that the gradients you see on the map above may be artifacts:

Nearly 30 years ago, Cavalli-Sforza et al. pioneered the use of principal component analysis (PCA) in population genetics and used PCA to produce maps summarizing human genetic variation across continental regions. They interpreted gradient and wave patterns in these maps as signatures of specific migration events. These interpretations have been controversial, but influential, and the use of PCA has become widespread in analysis of population genetics data. However, the behavior of PCA for genetic data showing continuous spatial variation, such as might exist within human continental groups, has been less well characterized. Here, we find that gradients and waves observed in Cavalli-Sforza et al.’s maps resemble sinusoidal mathematical artifacts that arise generally when PCA is applied to spatial data, implying that the patterns do not necessarily reflect specific migration events. Our findings aid interpretation of PCA results and suggest how PCA can help correct for continuous population structure in association studies.

A paper earlier this year took the earlier work further and used a series of simulations to show how the nature of the gradients varied. In light of recent preoccupations the results are of interest. Principal Component Analysis under Population Genetic Models of Range Expansion and Admixture:

In a series of highly influential publications, Cavalli-Sforza and colleagues used principal component (PC) analysis to produce maps depicting how human genetic diversity varies across geographic space. Within Europe, the first axis of variation (PC1) was interpreted as evidence for the demic diffusion model of agriculture, in which farmers expanded from the Near East ∼10,000 years ago and replaced the resident hunter-gatherer populations with little or no interbreeding. These interpretations of the PC maps have been recently questioned as the original results can be reproduced under models of spatially covarying allele frequencies without any expansion. Here, we study PC maps for data simulated under models of range expansion and admixture. Our simulations include a spatially realistic model of Neolithic farmer expansion and assume various levels of interbreeding between farmer and resident hunter-gatherer populations. An important result is that under a broad range of conditions, the gradients in PC1 maps are oriented along a direction perpendicular to the axis of the expansion, rather than along the same axis as the expansion. We propose that this surprising pattern is an outcome of the “allele surfing” phenomenon, which creates sectors of high allele-frequency differentiation that align perpendicular to the direction of the expansion.

The first figure shows the general framework with which they performed the simulations:

pcab1

You have a lattice which consists of demes, population units, all across Europe. They modulated parameters such as population growth (r), carrying capacity (C), and migration (m). Additionally, they had various scenarios of expansion from the southwest or southeast, as well as two expansions one after another to mimic the re-population of Europe after the Ice Age by Paleolithic groups, and their later replacement by Neolithic groups. They modulated admixture and introgression of genes from the Paleolithic group to the Neolithics so that you had the full range where the final European were mostly Neolithic or mostly Paleolithic.

Below are some of the figures which show the results:

allesurAs you can see the strange thing is that in some models the synthetic map gradient is rotated 90 degrees from the axis of demographic expansion! In this telling the famous synthetic map showing Neolithic expansion might be showing expansion from Iberia. Perhaps a radiation from a post-Ice Age southern refuge?

One explanation might be “allele surfing” on the demographic “wave of advance.” Basically as a population expands very rapidly stochastic forces such as random genetic drift and bottlenecks could produce diversification along the edge of the population wave front. The reason for this is that these rapidly expanding populations explode out of serial bottlenecks and demographic expansions, which will produce genetic distinctiveness among the many differentiated demes bubbling along the edge of expansion. Alleles which may have been at low frequency in the ancestral population can “fix” in descendant populations on the edge of the demographic wave of advance. This is the explanation, more or less, that one group gave last year for the very high frequencies of R1b1b2 in Western Europe. With this, they overturned the classic assumption that R1b1b2 was a Paleolithic marker, and suggested it was a Neolithic one.

Here’s their conclusion from the paper:

A previous study showed that the original patterns observed in PCA might not reflect any expansion events (Novembre and Stephens 2008). Here, we find that under very general conditions, the pattern of molecular diversity produced by an expansion may be different than what was expected in the literature. In particular, we find conditions where an expansion of Neolithic farmers from the southeast produces a greatest axis of differentiation running from the southwest to the northeast. This surprising result is seemingly due to allele surfing leading to sectors that create differentiation perpendicular to the expansion axis. Although a lot of our results can be explained by the surfing phenomenon, some interesting questions remain open. For example, the phase transition observed for relatively small admixture rates between Paleolithic resident and Neolithic migrant populations occurs at a value that is dependent on our simulation settings, and further investigations would be needed to better characterize this critical value as a function of all the model parameters. Another unsolved question is to know why the patterns generally observed in PC2 maps for our simulation settings sometimes arise in PC1 maps instead. These unexplained examples remind us that PCA is summarizing patterns of variation in the sample due to multiple factors (ancestral expansions and admixture, ongoing limited migration, habitat boundary effects, and the spatial distribution of samples). In complex models such as our expansion models with admixture in Europe, it may be difficult to tease apart what processes give rise to any particular PCA pattern. Our study emphasizes that PC (and AM) should be viewed as tools for exploring the data but that the reverse process of interpreting PC and AM maps in terms of past routes of migration remains a complicated exercise. Additional analyses—with more explicit demographic models—are more than ever essential to discriminate between multiple explanations available for the patterns observed in PC and AM maps. We speculate that methods exploiting the signature of alleles that have undergone surfing may be a powerful approach to study range expansions.

What’s the big picture here? In the textbook Human Evolutionary Genetics it is asserted that synthetic maps never became very popular compared to PCA itself. I think this is correct. But, the original synthetic maps have become prominent for many outside of genetics. They figure in Peter Bellwood’s First Farmers, and are taken as a given by many pre-historians, such as Colin Renfrew. And yet a reliance on these sorts of tools must not be blind to the reality that the more layers of abstraction you put between your perception and comprehension of concrete reality, the more likely you are to be led astray by quirks and biases of method.

In this case I do think first-order intuition would tell us that synthetic maps which display PCs would be showing gradients as a function of demographic pulses. And yet the intuition may not be right, and with the overturning of old orthodoxies in the past generation of inferences from the variation patterns in modern populations, we should be very cautious.

Citation: Olivier François, Mathias Currat, Nicolas Ray, Eunjung Han, Laurent Excoffier, & John Novembre (2010). Principal Component Analysis under Population Genetic
Models of Range Expansion and Admixture Mol Biol Evol

December 11, 2010

Excavating the Neolithic genetic strata

After linking to Marnie Dunsmore’s blog on the Neolithic expansion, and reading Peter Bellwood’s First Farmers, I’ve been thinking a bit on how we might integrate some models of the rise and spread of agriculture with the new genomic findings. Bellwood’s thesis basically seems to be that the contemporary world pattern of expansive macro-language families (e.g., Indo-European, Sino-Tibetan, Afro-Asiatic, etc.) are shadows of the rapid demographic expansions in prehistory of farmers. In particular, hoe-farmers rapidly pushing into virgin lands. First Farmers was published in 2005, and so it had access mostly to mtDNA and Y chromosomal studies. Today we have a richer data set, from hundreds of thousands of markers per person, to mtDNA and Y chromosomal results from ancient DNA. I would argue that the new findings tend to reinforce the plausibility of Bellwood’s thesis somewhat.

The primary datum I want to enter into the record in this post, which was news to me, is this: the island of Cyprus seems to have been first settled (at least in anything but trivial numbers) by Neolithic populations from mainland Southwest Asia.* In fact, the first farmers in Cyprus perfectly replicated the physical culture of the nearby mainland in toto. This implies that the genetic heritage of modern Cypriots is probably attributable in the whole to expansions of farmers from Southwest Asia. With this in mind let’s look at Dienekes’ Dodecad results at K = 10 for Eurasian populations (I’ve reedited a bit):


neolith

Modern Cypriots exhibit genetic signatures which shake out into three putative ancestral groups. West Asian, which is modal in the Caucasus region. South European, modal in Sardinia. And Southwest Asian, which is modal in the Arabian peninsula. Cypriots basically look like Syrians, but with less Southwest Asian, more balance between West Asian and South European, and far less of the minor components of ancestry.

Just because an island was settled by one group of farmers, it does not mean that subsequent invasions or migrations could not have an impact. The indigenous tribes of Taiwan seem to be the original agriculturalists of that island, and after their settlement there were thousands of years of gradual and continuous cultural change in situ. But within the last 300 years settlers from Fujian on the Chinese mainland have demographically overwhelmed the native Taiwanese peoples.

During the Bronze Age it seems Cyprus was part of the Near East political and cultural system. The notional kings of Cyprus had close diplomatic relations with the pharaohs of Egypt. But between the end of the Bronze Age and the Classical Age Cyprus became part of the Greek cultural zone. Despite centuries of Latin and Ottoman rule, it has remained so, albeit with a prominent Turkish minority.

One thing notable about Cyprus, and which distinguishes it from mainland Greece, is the near total absence of a Northern European ancestral component. Therefore we can make the banal inference that Northern Europeans were not initially associated with the demographic expansions of farmers from the Middle East. Rather, I want to focus on the West Asian and Southern European ancestral components. One model for the re-population of Europe after the last Ice Age is that hunter-gatherers expanded from the peninsular “refugia” of Iberia and Italy, later being overlain by expansions of farmers from the Middle East, and perhaps Indo-Europeans from the Pontic steppe. I have a sneaking suspicion though that what we’re seeing among Mediterranean populations are several waves of expansion out of the Near East. I now would offer the tentative hypothesis that the South European ancestral element at K = 10 is a signature of the first wave of farmers which issued out of the Near East. The West Asians were a subsequent wave. I assume that the two groups must correlate to some sort of cultural or technological shift, though I have no hypothesis as to that.

From the above assertions, it is clear that I believe modern Sardinians are descendants of that first wave of farmers, unaffected by later demographic perturbations. I believe that Basques then are a people who emerge from an amalgamation of the same wave of seafaring agriculturalists with the indigenous populations preceding them (the indigenes were likely the descendants of a broad group of northern Eurasians who expanded after the end of the last Ice Age from the aforementioned refugia). They leap-frogged across fertile regions of the Mediterranean and pushed up valleys of southern France, and out of the Straits of Gibraltar. Interestingly, the Basque lack the West Asian minority element evident in Dienekes’ Spaniards, Portuguese, as well as the HGDP French (even up to K = 15 they don’t shake out as anything but a two way admixture, while the Sardinians show a minor West Asian component). Also, the West Asian and Southern European elements are several times more well represented proportionally among Scandinavians than Finns. The Southern European element is not found among the Uyghur, though the Northern European and West Asian one is. I infer from all these patterns that the Southern European element derived from pre-Indo-European farmers who pushed west from the Near East. It is the second largest component across much of the Northwestern Europe, the largest across much of Southern European, including Greece.

A second issue which First Farmers clarified are differences between the spread of agriculture from the Near East to Europe and South Asia. It seems that the spread of agriculture across South Asia was more gradual, or least had a longer pause, than in Europe. A clear West Asian transplanted culture arrived in what is today Pakistan ~9,000 years ago. But it does not seem that the Neolithic arrived to the far south of India until ~4,000 years ago. I think that a period of “incubation” in the northwest part of the subcontinent explains the putative hybridization between “Ancient North Indians” and “Ancient South Indians” described in Reconstructing Indian population history. The high proportion of “Ancestral North Indian,” on the order of ~40%, as well as Y chromosomal markers such as R1a1a, among South Indian tribal populations, is a function of the fact that these groups are themselves secondary amalgamations between shifting cultivators expanding from the Northwest along with local resident hunter-gatherer groups which were related to the ASI which the original West Asian agriculturalists encountered and assimilated in ancient Pakistan (Pathans are ~25% ASI). I believe that the Dravidian languages arrived from the Northwest to the south of India only within the last 4-5,000 with the farmers (some of whom may have reverted to facultative hunter-gathering, as is common among tribals). This relatively late arrival of Dravidian speaking groups explains why Sri Lanka has an Indo-European presence to my mind; the island was probably only lightly settled by farming Dravidian speakers, if at all, allowing Indo-European speakers from Gujarat and Sindh to leap-frog and quickly replace the native Veddas, who were hunter-gatherers.

Note: Here is K = 15.

* Wikipedia says there were hunter-gatherers, but even here the numbers were likely very small.

December 3, 2010

The great northern culture war

A new paper in The New Journal of Physics shows that a relatively simple mathematical model can explain the rate of expansion of agriculture across Europe, Anisotropic dispersion, space competition and the slowdown of the Neolithic transition:

The front speed of the Neolithic (farmer) spread in Europe decreased as it reached Northern latitudes, where the Mesolithic (hunter-gatherer) population density was higher. Here, we describe a reaction–diffusion model with (i) an anisotropic dispersion kernel depending on the Mesolithic population density gradient and (ii) a modified population growth equation. Both effects are related to the space available for the Neolithic population. The model is able to explain the slowdown of the Neolithic front as observed from archaeological data

The paper is open access, so if you want more of this:
fareq

Just click through above. Rather, I am curious more about their nice visualization of the archaeological data:


euroneolithic

Note how much variance there is in terms of the rate of change of the clines. As I’ve observed before there was a “break out” of the LBK farmers into Central Europe nearly 7,000 years ago, but it took much longer to close the gap between the farms on the frontier and the sea. This is well known from the archaeology, as there seems to have been a pause of ~1,000 years across much of the north European plain. On the scale of 10,000 years that’s not much time, but that’s about 40 generations. In Frisia it looks like the spreading of farming stopped for nearly ~2000 years!

Why the abatement of the spread of farming? I think the authors of the above paper are correct in their acceptance of the conventional wisdom of greater Mesolithic densities in Northern Europe. But I think perhaps a better description might be maritime Northern Europe. We often imagine early farmers displacing hunters and gatherers of game and herb, but what if in much of the world the main clash numerically was between dense populations oriented toward the sea, and those who were depended on the land? About seven years ago a study came out which argued for a rapid transition from seafood to meat in the diets of early Britons, Why Did Ancient Britons Stop Eating Fish?:

When cattle, sheep, pigs, and wheat arrived on the shores of Great Britain about 5,000 years ago, fish quickly fell off the Neolithic menu, according to an analysis of human bones scattered throughout the island.

“Farming really took off in Britain during the Neolithic. The main questions concerning the speed of change relates to how quickly Mesolithic peoples adapted—or otherwise—to the new farming methods and/or the spread of farming into Britain by new farming communities,” he said.

The research by Richards and colleagues Rick Schulting at Queen’s University Belfast and Robert Hedges at the University of Oxford tracks the shift in diet by examining the dietary signature stored in the bones.

They find that the shift was rapid and complete at the onset of the Neolithic. “Marine foods, for whatever reason, seem to have been comprehensively abandoned,” the researchers conclude in the September 25 issue of the journalNature.

“We determined that after the introduction of domesticates, as well as the other artifacts associated with the Neolithic, the isotope values showed that marine foods were not used anymore,” he said. “We then infer that this is a switch from wild foods such as fish and shellfish to the new domesticates that arrive at this time.”

Richards said there are three plausible reasons why the British abandoned seafood from the beginning of the Neolithic: the domesticated plants and animals presented a steady source of food; the shift was forced by a climate change; or cultural pressure.

In the early 2000s the idea of wholesale rapid demographic replacement was not in the air. I think we need to put that back on the table. Here is the chart on isotope ratios from the 2003 paper:
culwar

Notice the sharp discontinuity. Richards et al. in 2003 interpreted this as a rapid cultural acquisition of the Neolithic lifestyle ~2500-3000 BC. They note in the media reports that later Britons, for example at the time of the Roman conquest, seem to have utilized fish a bit more in their diet than these early Neolithics. This stands to reason, much of Britain is not too far from the sea. To me the very sharp drop in marine consumption is indicative more of a food taboo, than a practical shift. Obviously farmers would primarily be subsistent on grain, but there’s no necessary reason to avoid meat or fish, but as it happens in many parts of the world societies preserve and perpetuate exactly such norms. These norms may have spread through cultural diffusion, for example through an adoption of a new religion. Or, the norms may have been brought by a new group which arrived in large numbers and replaced the indigenous population.

Here is an equivalent chart from Denmark from an earlier paper by the same group:

denmark

800px-Saami_Family_1900pacnortWhen we think of peoples who aren’t farmers, we often think of marginalized nomadic or semi-nomadic groups. Many of the remaining hunter-gatherers such as Bushmen, as well societies which supplement their conventional lifestyle with a lot of hunting & gathering, such as the indigenous peoples of Siberia or the Sami of northern Scandinavia, occupy territory which is simply not viable for conventional agriculture. But this was not so in the past. Before the farmers arrived the rich bottom-lands were occupied by hunters & gatherers, of fish, game, grain, and nuts. In certain ecologies, such as around productive estuaries one could imagine enormous aggregations of these peoples. Additionally, it seems likely that a sedentary lifestyle predates farming. A good contemporary analog for what ancient Northern Europe may have been like was the Pacific Northwest before the European settlement. These native tribes were relatively affluent because of the abundance of salmon runs, and engaged in lavish signalling, such as with their famous potlatches. Seeing as how there are Atlantic salmon runs in places like Norway and Scotland one can make even closer correspondences perhaps!

Stonehenge-GreenAs I have stated before just because we have no written records of this period, we can not assume that these were necessarily the fragmented and scattered “small-scale societies” which we’re familiar with today. There may have been ideologically motivated political coalitions and alliances which broke down along ethnic and cultural lines. In the paper above the authors argue that there is evidence that a climatic constraint, crops which do not have a good yield in cooler or warmer temperatures, is a weak hypothesis. If so I wonder if it is a bit too pat to simply model the dynamics as a diffusive “bottom up” process. Seems plausible enough for much of Europe where Mesolithic populations were thin on the ground because of local carrying capacity, but I suspect that the encounter between dense agglomerations of farmers and fishermen resulted in an inevitable ramp up of political integration and consolidation, as villages and tribes had to coordinate together because of a positive feedback loop of conflict.

Image Credit: Lordkinbote, Mactographer

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