The Unz Review - Mobile
A Collection of Interesting, Important, and Controversial Perspectives Largely Excluded from the American Mainstream Media
Email This Page to Someone

 Remember My Information



=>
Authors Filter?
Razib Khan
Nothing found
 TeasersGene Expression Blog
/
Neolithic Revolution

Bookmark Toggle AllToCAdd to LibraryRemove from Library • BShow CommentNext New CommentNext New Reply
🔊 Listen RSS

Dienekes has a post up highlighting a preprint out of Pontus Skoglund’s group. It is titled Ancient genomes mirror mode of subsistence rather than geography in prehistoric Europe. It doesn’t seem to be online (fingers crossed that it shows up linked at Haldane’s Sieve soon). In any case I am not surprised by the broad outlines of the thesis. And, it is not as if Skoglund’s group is the only one working in this area, I have suspicions that others are finding something very similar. These results out of Europe are probably reflective of the fact that much of the model in Peter Bellwood’s First Farmers is generally correct, the emergence of an agriculture revolution in a few select world societies produced a cultural and demographic revolution.

But one can take things too far, and I think Bellwood did. The results above, and elsewhere, also confirm that there was not total demographic replacement. In many regions the agriculturalists absorbed the hunter-gatherers. Using light coverage of whole genomes Skoglund’s group inferred that the farmers who arrived in prehistoric Europe from the Middle East seem to have contributed most of the ancestry of Southern Europeans, and also match nearly perfectly the genetic profiles of farming populations in Scandinavia. In contrast, ancient hunter-gatherers in Scandinavia and prehistoric Spain resemble contemporary Baltic groups (e.g., Lithuanians, Finns, and Scanadinavians). Finally, they conclude that modern Scandinavians are slightly more close to ancient hunter-gatherers than the farmers. This implies substantial farmer admixture in demographic terms. The group notes that previous inferences of Middle Eastern admixture were compromised by the fact that modern groups often exhibit African admixture. When you look only at the non-African portion, they are a much better proxy. One reason I am curious about the preprint in full is that I believe that even removing African admixture, one might be biased by selection of ‘reference’ populations. It seems likely that there were major eruptions from Arabia in antiquity and the medieval period (inferred by comparing religious isolates such as Arab Christians with their Muslim neighbors).

Setting aside that a two-way admixture seems unlikely to be the whole story*, it does offer up a way to explore an interesting question: on what sort of genes do hunter-gatherers and farmers differ? Specifically I’m wondering about utilizing admixture mapping. In Scandinavian populations regions of the genome where there are adaptations for farming are localized should be enriched for farmer ancestry, and vice versa for hunter-gathering. In the case of Northern Europeans farmers moved up latitudinal clines, and adapted to local conditions only halting. This explains in part that it seems Iberia and parts of Western Europe have more farmer ancestry than regions of Northeast Europe which are closer to the original zone of expansion as the crow flies. Not only did the hunter-gatherers have some cultural traits which conferred benefits in the deep north, but likely there were particular adaptations in these climes which aided their survival.

I understand that admixture mapping for populations which have mixed (and frankly were not that genetically different in the first place) may be difficult. But linkage disequilibrium based methods have been pushed much further back than I could have imagined, and it has been done with South Asians in regards to “Ancestral Northern Indian” vs. “Ancestral South Indian” ancestry and genetic functionality (specifically disease risk alleles).

* In addition, I am more skeptical of a simple demic diffusion model than I was in the past. I think there may have been multiple demographic pulses, followed by equilibration phases.

(Republished from Discover/GNXP by permission of author or representative)
 
🔊 Listen RSS

Over at Scientific American Eric Michael Johnson has a very long post up, The Case of the Missing Polygamists. It is a re-post of something he already published at Psychology Today a few years ago. Though provisionally a review of Sex at Dawn, Johnson covers a lot of ground, and also has extensive quotations from Sarah Blaffer Hrdy.

I’m reflecting upon the post for a second time because it is very rich in ideas, and lays out may different general concepts and specific propositions. The bottom line from what I can gather is that Johnson agrees with those thinkers who believe that agriculture and the Neolithic revolution to a great extent reshaped social relations, and give us a skewed perception of “normal” human societies. I’m not going to rehash all of the points in the piece, but will focus on just a few which I think I can extend upon fruitfully.


Long time readers of this weblog know that I tend to accept that something radical shifted during the Neolithic revolution. I’m of the opinion that like most animals humanity’s state was Malthusian during the age of hunter-gatherers, and of farmers. That is, gains in population eventually absorbed productivity increases due to technology (e.g., bow and arrow) or surplus land (e.g., settlement of the New World by humans). But different forms of Malthusianism can obtain different stable states. The rhythm of life of a Chinese peasant and a Bushmen are very different, despite the fact that both may operate on the Malthusian subsistence margin. Malthusianism is a end point, it does not specify the dynamic by which one proceeds toward it.

Johnson relays the idea that prior to agriculture humanity had a matrifocal and de facto polyamorous bias. For the purposes of my thought here we need to separate the social and biological. In the social sense matrifocality simply means that males move between focal groups, while females remain in their natal groups. Polyamory implies that males and females may have multiple sexual relationships. In a genetic sense matrifocality should imply that Y chromosomes flow between groups (lower Fst), and mitochondrial lineages exhibit greater geographical constraint (higher Fst). In the longer term equitable pure polyamory would not be genetically distinguishable from pure equitable momogamy (because of more combinations in the former case there may be more diverse autosomal haplotypes, but I’m not sure this is very relevant for this discussion).

It isn’t innovative or surprising for someone to assert that agriculture was a major rupture in human history. Major public intellectuals routinely take a shot at characterizing what made it so special, and it’s a lively area of scholarship. Rather, I will reiterate here what I have held for many years: the “traditional” and normative social systems common among civilized societies since the rise of agriculture and the emergence of mass society are cultural adaptations which serve to constrain impulses which are deeply hard-wired within our species. Elite lineages the world over arranged the pair bonds of their offspring for many generations, and yet this often meets resistance, or at least resignation. The tales of adulterous lovers subject to a tragic fate are common literary motifs. This is I suspect an aspect of evoked culture, the inevitable tension between our deep impulses driven by individual preferences, and the social obligations which many have to had fulfill as part of extended kinship networks which had accrued prestige and capital. Both of these are human universals, as are the consequences. The high culture literature records this tension, and elaborates upon it so as to model proper and correct behavior for elites so as to avoid tragedy.

I have no doubt that hunter-gatherer societies had lineages which accrued prestige and capital. The modern hunter-gatherer societies which Eric Michael Johnson highlights are not representative of the human past. They have been relegated to marginal land. In the past hunter-gatherer societies drew upon lands with greater primary productivity, so the chasm between themselves and their farming successors in terms of physical capital and social stratification was often less than we may expect using the modern relics as references. But, agriculture clearly signaled a shift in scale and quantity. Super-male lineages, such as that of Genghis Khan, are possible only due to the contingent conditions of civilization, in particular all the elements necessary for globalism. Agriculture was likely an amplification of a “winner take all” dynamic in the game of social positioning. And not surprisingly these societies also developed complex belief systems and institutions to moderate and dampen these tendencies, likely due to their innate instabilities, as well as a human bias toward egalitarianism (i.e., land redistribution and opposition to inequality is a tendency in many societies at the commanding heights, while world religions all exhibit an anti-Nietzschean bent, for lack of a better term).

The reason that “Western culture” with its individualist ethos is so attractive, and threatening, is that in many ways it is a purer reflection of the impulses which were operative in the ancestral environment. I am not here talking about the most extreme manifestations of Western liberality in sexual mores, such as gay marriage or formal polyamory (most people do not crave homosexual relations). Rather, a modicum of personal choice and sexual egalitarianism, are out of keeping with the norms which were necessary to maintain social order in the period between small-scale hunter-gatherer societies and the rise of the mass consumer society. On the margins of subsistence in a world of farmers individual action may redound very negatively upon the broader kinship group, so personal norms of honor and propriety may be highly developed.

And yet if these cultural norms were so strong why did humans not evolve their way out of their hunter-gatherer ethos? There are two primary reasons for this. First, for much of human history the norms outlined in high culture texts and religions were applicable only to elite lineages. This is history recorded in the texts, but it may not be most of lived human history. For example, religious marriages in much of medieval Europe were obligate for noble families, but may not have been for peasants, who made recourse to common law relationships. Bastardy is less of a concern in scenarios where property divisions are of no consequence. There’s no property to inherit. But, this phenomenon is probably moderated by the fact that over much of history elite lineages may have been more fecund than the masses. Lived history may be more ephemeral than we realize in a genetic sense.

A second explanation though is that the very tendencies which make adherence to traditional norms somewhat discomforting on an individual level are necessary in other contexts. Love is an inconvenience when it comes to arranging marriages for your offspring optimally on a social dimension, but it may be necessary for men and women to invest in their offspring due to the love they feel for them so that they live and flourish. In other words, psychological impulses which were inconvenient in one domain were necessary and adaptive on others. Phenotypically I’m implying that there was functional constraint, and genetically it would manifest as pleiotropy. I suspect that a strong tendency toward developing loving bonds with children is a much more important characteristic in these elite lineages than dampening the initial discomfort that may occur when one is paired off with someone with whom one is not particularly enamoured. In a social and biological evolutionary sense romantic love is less important than we might think in our individualist age. But, romantic love remains hard-wired within us because it is biologically impossible to suppress its manifestation so long as we need the emotion of love more importantly to bind us together with children.

Finally, let’s go back to Johnson’s treatment of the disjunction between idealized polyamory and realized polygyny in the ancient environment (at least to a mild extent). By this, he points to the reality that some of the Y chromosomal data point to a reproductive skew, where a few males tend to give rise to a disproportionate number in the next generation. In extreme polygyny you have a Genghis Khan situation, where males of one narrow lineage have an enormous reproductive advantage. The scenario sketched out in Johnson’s post is that females may have had relationships with several males (and the inverse), but there was a tendency toward favoring reproduction with one focal male or female. This does not seem to negate the reality of jealousy and drama. We see this among common chimpanzees, who have a classic mating system in the extreme sense outlined by Johnson (this species has huge testicles to generate viscous sperm the competition is so extreme). And modern polygamorists who have formal relationships all tell tales of enormous time investments necessary to maintain proper relationship equilibrium. This is I think the reason that elite lineages in mass agricultural societies turned toward simpler relationship networks. The older model was simply not sufficiently stable for the purposes of maintaining the social and cultural systems necessary for the proper functioning of the older Malthusian civilizations. This is evident when conflicts within elite lineages are often rooted in questions of paternity and maternity (half siblings; Charles Martel was the bastard son of his father, who superseded the legitimate line), or accusations of false paternity (the first Chinese Emperor was subject to this rumors due to his bad reputation in later generations).

Where does this lead us? I think it’s complicated. Many social conservatives would argue that you can’t just dispense with the whole cultural toolkit which has organically evolved over the last 10,000 years, and revert back to the more primal state of affairs before agriculture. Social liberals point out that the forms of the past are no longer necessary in the present. But though affluence has removed many necessary social constraints, we have not warped ourselves back to the Paleolithic either. The balance between our instincts, which evolved in small groups thousands of years ago, and our notional cultural mores, which crystallized during the Axial Age, is still a work in progress. I believe that the world religions were version 1.0 in regards to formalizing workable compromises between our basic natures and the realities of the aristocratic world. What we need is a version 2.0, where we balance the needs of the common person on the street, with their basic impulses. The great compromise between our biology and our current social complexity will continue. But it is a dynamic parameter, not a static element.

(Republished from Discover/GNXP by permission of author or representative)
 
🔊 Listen RSS

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 the USA). A final interesting point is that the authors note that today we are seeing the last gasp of this transition toward large numbers of children, as fertility drops toward replacement all across the world. That too may have some cultural consequences.

Here’s a podcast with the author. Link via Dienekes.

(Republished from Discover/GNXP by permission of author or representative)
 
🔊 Listen RSS

ResearchBlogging.org Seriously, 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 the New World in large part was the union between non-European women and European men. These are hard brutal myths and hard brutal facts. But do they reflect an essential aspect of the dynamics which have shaped our species’ past?

I’m not willing quite yet to add a confident weight upon this possibility, but this seems to be part at least part of the picture. You see a major disjunction on male and female lineages among South Asians for example. A new paper in PNAS adds weight to this possibility, albeit only incrementally. Ancient DNA reveals male diffusion through the Neolithic Mediterranean route:

The Neolithic is a key period in the history of the European settlement. Although archaeological and present-day genetic data suggest several hypotheses regarding the human migration patterns at this period, validation of these hypotheses with the use of ancient genetic data has been limited. In this context, we studied DNA extracted from 53 individuals buried in a necropolis used by a French local community 5,000 y ago. The relatively good DNA preservation of the samples allowed us to obtain autosomal, Y-chromosomal, and/or mtDNA data for 29 of the 53 samples studied. From these datasets, we established close parental relationships within the necropolis and determined maternal and paternal lineages as well as the absence of an allele associated with lactase persistence, probably carried by Neolithic cultures of central Europe. Our study provides an integrative view of the genetic past in southern France at the end of the Neolithic period. Furthermore, the Y-haplotype lineages characterized and the study of their current repartition in European populations confirm a greater influence of the Mediterranean than the Central European route in the peopling of southern Europe during the Neolithic transition.

First, the easy stuff. This is another datum which should make us skeptical of the idea of Neolithicization as an overwhelmingly indigenous process, spreading via cultural emulation. The Y chromosomal lineages sequenced here are very homogeneous, and seem to belong to a patrilocal kinship group. In contrast, the mtDNA lineages, which tell us about female ancestry, are much more diverse. They cover a much better sweep of contemporary European genetic diversity. The authors note that a minority of mtDNA lineages are of Middle Eastern origin, but the majority are of lineages which are presumed to have a deeper Paleolithic root, as supported by their greater variance. I think we should still be cautious of even this interpretation, but there does seem to be a notable difference in this one community between males and females which may be indicative of a particular social and cultural system.

The maps to the left show the relationship of mtDNA and Y lineages to modern patterns of European genetic variation. The darker the shading the higher proportion of lineages shared. The top figure illustrates female mtDNA, and you can see the broad correspondences between the ancient southwest French sample and modern groups. But observe the big difference in the second figure, which shows the male distributions. This is much more localized to particular regions of Iberia and Turkey. The overwhelming haplogroup in the cemetery was G2a-P15, which is rather rare in Europe today, and the region. What happened to these men? Genetic drift or population replacement perhaps. If one posits a model of long term smaller male effective populations then Y chromosomal lineages will be subject to more stochastic extinction and fixation events than mtDNA. I’m not sure if I believe this, but that is one model which doesn’t necessarily involve a conventional replacement of the male lineages a la Conan.

But the dispersal of G2a-P15 at low frequencies around the Mediterranean is also consistent with the possibility of repeated replacement of male lineages across the arc of history. This has historical precedent, the Greek colonies alonge fringes of the Mediterranean were founded by men, sometimes explicitly exiled from their home polis. They had often had to “obtain” local women to perpetuate themselves. This isn’t supposition or conjecture, but outlined in some of the texts which record how colonies were founded in the Archaic pre-Classical period. Of course we do know that these sorts of transplantations could also involve women, they seem to have in the case of the Etruscans.

Additionally, this may also be a case of male “leap-frog” migration patterns, which break apart the null model of genetic variation which is modeled by isolation-by-distance. The argument is that the expansion of farming from the eastern Mediterranean did not occur via demic diffusion by land, but rather through a process of maritime transplantation, and then subsequent expansion from the nascent nuclei. Again, we can look at the expansion of the maritime Greeks. There was no contiguous region of Greek settlement between Greece proper and “Magna Graecia” in southern Italy and Sicily. Connections were by sea, which makes sense insofar as long distance sea transport was far cheaper energetically than land migration. I see no reason why these ancient farming Diasporas couldn’t have maintained a sort of cultural continuity for centuries through ritual or regular contacts via maritime transit.

A second point in this paper is that this population seems to have lacked in totality the allele which is diagnostic of lactase persistence across much of Europe today. The authors observe that that allele has a frequency of ~43% in the modern French population (it’s dominant, so that means that ~35% of the French are lactose intolerance). I would be curious about the frequency in the south of France, as traditionally the north of France was the domain of butter, while that to the south more of olive oil (historically the south of France witnessed the preservation of the Gallo-Roman aristocracy, which explicitly adopted Frankish modes of dress in 5th century as a way to assimilate into the non-clerical administrative apparatus of the Merovingian monarchy, but maintained their cultural distinction). The authors conclude from the lack of the LP allele that the individuals buried in the cemetery were from a different migration stream than those which founded the LBK society in central Europe, and who may have invented the dairy culture.

I think the “big picture” that is shaping up is that there were multiple intrusions, eruptions, replacements, and assimilations, across prehistoric Europe, just as there were across many regions of the world. On the whole I suspect males played more of a role in this process than females, though I’m not confident that we will see a consistent pattern of female lineages in a given area being markers for the Paleolithic populations. There may have been so much shifting and layering that the original people, the oldest of old, may only be accessible via ancient DNA. Speaking of which, thank god we’re finally entering the golden age of ancient DNA! Many questions will no doubt finally be resolved.

Dienekes Pontikos also has a lot to say about this. I’m sure some of you who are more versed in mtDNA and NRY haplogroups will also offer you 2 cents!

Citation: Marie Lacan, Christine Keyser, François-Xavier Ricaut, Nicolas Brucato, Francis Duranthon, Jean Guilaine, Eric Crubézy, & Bertrand Ludes (2011). Ancient DNA reveals male diffusion through the Neolithic Mediterranean route PNAS : 10.1073/pnas.1100723108

(Republished from Discover/GNXP by permission of author or representative)
 
🔊 Listen RSS

ResearchBlogging.orgThe Pith: Over the past 10,000 years a small coterie of farming populations expanded rapidly and replaced hunter-gatherer groups which were once dominant across the landscape. So, the vast majority of the ancestry of modern Europeans can be traced back to farming cultures of the eastern Mediterranean which swept over the west of Eurasia between 10 and 5 thousand years before the before.

Dienekes Pontikos points me to a new paper in PNAS which uses a coalescent model of 400+ mitochondrial DNA lineages to infer the pattern of expansions of populations over the past ~40,000 years. Remember that mtDNA is passed just through the maternal lineage. That means it is not subject to the confounding dynamic of recombination, allowing for easier modeling as a phylogenetic tree. Unlike the autosomal genome there’s no reticulation. Additionally, mtDNA tends to be highly mutable, and many regions have been presumed to be selectively neutral. So they are the perfect molecular clock. There straightforward drawback is that the history of one’s foremothers may not be a good representative of the history of one’s total lineage. Additionally the haploid nature of mtDNA means that genetic drift is far more powerful in buffeting gene frequencies and introduced stochastic fluctuations, which eventually obscure past mutational signals through myriad mutations. Finally, there are serious concerns as to the neutrality of mtDNA…though the authors claim to address that in the methods. I should also add that it also happens to be the case that there is less controversy and more surety as to the calibration of mutational rates of mtDNA than the Y chromosomal lineages of males. Their good for determining temporal patterns of demographic change, and not just tree structures.

Here’s the abstract, Rapid, global demographic expansions after the origins of agriculture:

The invention of agriculture is widely assumed to have driven recent human population growth. However, direct genetic evidence for population growth after independent agricultural origins has been elusive. We estimated population sizes through time from a set of globally distributed whole mitochondrial genomes, after separating lineages associated with agricultural populations from those associated with hunter-gatherers. The coalescent-based analysis revealed strong evidence for distinct demographic expansions in Europe, southeastern Asia, and sub-Saharan Africa within the past 10,000 y. Estimates of the timing of population growth based on genetic data correspond neatly to dates for the initial origins of agriculture derived from archaeological evidence. Comparisons of rates of population growth through time reveal that the invention of agriculture facilitated a fivefold increase in population growth relative to more ancient expansions of hunter-gatherers.

As Dienekes notes until recently the orthodoxy was that the genetic variation of modern populations was well explained by the genetic variation of Paleolithic groups after the Last Glacial Maximum ~20,000 years B.P. In this line of thought agriculture spread often by cultural diffusion, and the first local adopters in a region would then enter into a phase of demographic expansion. Bryan Sykes’ Seven Daughters of Eve and Stephen Oppenheimer’s The Real Eve are expositions of this point of view, which really was the historical genetic mainstream. This also dovetailed with the anthropological bias of “pots-not-people,” whereby cultural forms moved through transmission and not migration. There were some dissenters, such as Peter Bellwood, but by and large the genetic evidence at least was robust enough that they could be dismissed.

So what happened? Several things. First, the sample sets of mtDNA and Y chromosomes kept getting larger. There was deeper sequencing of informative regions. Thick SNP-chip autosomal studies came to the fore, with different conclusions. Finally, ancient DNA extraction allowed scientists to compare the real lineages of hunter-gatherers in ancient Europe vs. what they had presumed were hunter-gatherer descendant lines in modern Europeans. The strong disjunction often found was indicative of a major failing in the prior assumptions of the theorists of the early 2000s: that they could infer confidently past events from the palimpsest of modern genetic variation. They couldn’t. We know that because they seem to have been wrong.

Let’s give India as an example of “what went wrong.” Here’s a paper from 2005, Most of the extant mtDNA boundaries in South and Southwest Asia were likely shaped during the initial settlement of Eurasia by anatomically modern humans:

Since the initial peopling of South and West Asia by anatomically modern humans, when this region may well have provided the initial settlers who colonized much of the rest of Eurasia, the gene flow in and out of India of the maternally transmitted mtDNA has been surprisingly limited. Specifically, our analysis of the mtDNA haplogroups, which are shared between Indian and Iranian populations and exhibit coalescence ages corresponding to around the early Upper Paleolithic, indicates that they are present in India largely as Indian-specific sub-lineages. In contrast, other ancient Indian-specific variants of M and R are very rare outside the sub-continent.

The Upper Paleolithic is pre-Holocene. I generally accepted this, until the the studies came out from the SNP-chips which had hundreds of thousands of autosomal markers. To be short about it Indians just seemed too close to West Eurasians if the mtDNA results were correct, and, representative. In fact, if Reconstructing Indian History is correct, about half the South Asian genome in aggregate is very close to that of West Eurasians, to the point where it seems likely to have a common ancestry in the Holocene. The mistaken inference from mtDNA may be due in part to sex-biased gene flow. That is, the South Asian exogenous genome was strongly biased toward male migration, while the deep time mtDNA substrate has tended to persist underneath all these successive layers.

Moving to the paper in question, they use a “Bayesian skyline” method to reconstruct past demographic history. Specifically, the history of the direct maternal lineage. We wouldn’t really pay attention if they didn’t have interesting results. And they do indeed.

The table is rather straightforward. They partitioned the samples they had into putative hunter-gatherer and Neolithic lineages. Notice the difference. For some of these cases we have very robust non-genetic evidence of expansion. This is true especially for the African and Southeast Asian Holocene cases. Their methods here predict exactly what we already know. So the key value add is that the methods are predicting something which is more in dispute: the demographic history of contemporary European mtDNA lineages. The concordance of the archaeological evidence of the Neolithic transition in Europe and the inferred demographic expansion of European Neolithic mtDNA lineages is striking.

The plot to the left is the curve of demographic expansion predicted from their method for Neolithic and Paleolithic lineages in Europe. The y-axis is log-scaled, so it naturally understates the explosive growth of Neolithic lineages. It comports well with what we know of how agricultural societies tend to expand and stabilize over time. During a phase of “land surplus” they enter into rapid demographic expansion, forcing the frontier of settlement out. Once the land is “filled up” we enter into the classic Malthusian “stationary state,” where the grinding misery of the peasantry becomes the lot of most. In contrast hunter-gatherer lineages didn’t experience such an explosive shift. Though pre-modern hunter-gatherer landscapes were more diversified than what we experience today, because they had access to the rich “bottom lands” and seashores now monopolized by agriculturalists, the carrying capacity of the land was generally lower for their lifestyle, and waxed and waned more gradually with shifts in ecology.

The authors also did some neat geo-visualization, if I do say so (and I’m jealous!). The two panels illustrate the spread of agriculture as inferred from archaeology, and the rate of population growth calculated from the joint information of the time of onset of a farming lifestyle in a region and the point on the “growth curve” for the Middle Eastern lineages at that time. So above you see the spread of agriculture from the eastern Mediterranean from 8000 BC to 2500 BC. Then, you see a geographical illustration of the S-shaped growth curve of the farmers. Their initial colonies experienced modest growth, but there was a transition zone in the middle of rapid expansion. Why? Perhaps there was a necessary critical mass, before the superiority of numbers began to wear down the hunter-gatherers. But this itself was a transient, as the farmer societies ran up against the limits of ecology along the northern European plain (or, perhaps just as likely, they encountered dense hunter-gatherer societies which were able to temporarily withstand their aggressive expansion on the European maritime fringe). I suspect that the models are more complex than a one-two punch, in either time or space. There were likely several pulses and distinct streams coming out of the Middle East which populated Europe.

They conclude that “Mesolithic ancestry makes up only a fraction of contemporary European genomes. U5a, U5b1, V, and 3H combined account for ≈15% of western Europeans mtDNA haplogroups.” Note that U5a and U5b are modal among the Finnic peoples of Europe. V seems widely distributed, and modal in northern Scandinavia and the western Mediterranean. I can’t seem to find easy information on 3H.

From the supplements here are the European haplgroups they selected:

We chose haplogroups associated with an origin in Near Eastern populations during the Holocene: T1, T2, J1a, K2a, and H4a. These haplogroups (T1, T2, J1a, and K) all appear to have Near Eastern founders that migrated to Europe after the Younger Dryas (2). After inspecting the haplogroup K network in Behar et al. (4), we chose the subgroup K2a, which appears to be present in the Near East (including non-Ashkenazi Jews) and European populations (but not North Africa). Haplogroup H4a is thought to have expanded throughout Europe during the Neolithic (5). However, the location of its origin is still not certain (6). Removing H4a from the Skyline analysis did not substantively change the timing of Holocene period expansion (results not shown). European haplogroups U5, V, and 3H are associated with an indigenous origin in Europe (2). Haplogroups U5a, U5b1, V, and 3H have all been attributed a TMRCA during the Last Glacial Period (2, 7–9)

Readers more well versed in the literature on mtDNA haplogroups can pick these details apart.

Where does this leave us? If this and other recent papers are correct. then the expansion of farming to Europe from the Middle East resembles the settlement of the New World far more than we may have thought! In some regions there was likely near total replacement of the substrate, perhaps like the United States. In others there was modest uptake of the indigenous substrate, as is the case in Argentina. Finally, there were regions where the indigenous hunter-gatherer substrate may have persisted to a far greater extent. I think this may be the case mostly in Baltic Europe, which combined both the possibility of relatively high hunter-gatherer carrying capacities because of marine resources and a climatic regime rather unsuitable to the initial Middle Eastern crops.

Citation: Gignoux CR, Henn BM, & Mountain JL (2011). Rapid, global demographic expansions after the origins of agriculture. Proceedings of the National Academy of Sciences of the United States of America, 108 (15), 6044-9 PMID: 21444824

(Republished from Discover/GNXP by permission of author or representative)
 
🔊 Listen RSS

About five months ago I read Peter Bellwood’s First Farmers: The Origins of Agricultural Societies. Bellwood’s thesis is simple: that the first adopters of farming entered into a period of rapid demographic expansion and by and large replaced non-farming groups. The populations which dominate the world today in this model are then the descendants of the very small set of cultures which ~10,000 years ago triggered the Neolithic Revolution. When Bellwood presented his thesis in the mid-2000s many would have dismissed it out of hand. Today I believe we have to take this model seriously.

There are two primary reasons from my perspective why I am now thinking about Bellwood’s thesis a great deal. First, the archaeogenetic inferences based on distributions of modern allele frequencies which suggested that the Neolithic Revolution in Europe was a matter of cultural diffusion seem far shakier. With such genetic models no longer taken for granted the recent historical, semi-historical, and ethnographic evidence, on farming transitions must be given much more weight. The case of the Bantu expansion in Africa seems to be semi-historical. The Bantu farmers themselves were not literate but their wave of advance was in historical time. Tellingly, the Bantu speaking populations of Southern Africa are genetically more similar to the Fang of Cameroon then they are to the Khoisan to their west! More well documented has been the attempts by Europeans to settle various lands overseas in their colonial adventures. They have been able to marginalize populations which did not habitually practice intensive agriculture relatively easily (note that the locus of Afrikaner settlement was initially around the Cape, where Bantu influence was minimal and Khoikhoi pastoralists were dominant). In contrast, in regions like Mesoamerica where obligate intensive agricultural civilization had deep roots there was no biological replacement, but hybridization.

An argument can be made that the initial farmers did not have so many advantages over their hunter-gatherer neighbors. So the power and force of the mass agricultural way of life which bore down upon the indigenes of Australia was qualitatively different because the Europeans who arrived were the outer wave of an ancient and ruthlessly efficient civilization of farmers, honed to brutal perfection through the cauldron of inter-group competition over thousands of years. I think the best counter argument against this is the evidence of rapid sweeps of cultural forms in European in prehistory, as well as rapidity of the success of the Bantu agricultural toolkit.

The new genome blogger Diogenes expresses the thesis of agricultural replacement to near maximal levels in the model which he is attempting to test with ADMIXTURE runs. Here are his propositions (formatting reedited for clarity):

1. The Neolithic Revolution was about a significant change in Humans. I happened due to selection over thousands of years in very few very special and uniquely rich and unstable environments around the world. This change influenced and was influenced mutually and gradually by technology and culture of the originally Forager people subjected to it. [agree, Razib]

2. Agricultural lifestyles allow for at least 10x higher population differences. Imagine for once this theoretical unreal situation: A land divided as a chess board into 10 squares; 5 inhabited by Neolithic people at 10ppl per square and 5 by Forager people at 1 person per square exclusively. Now imagine they mix. Total resulting population 10×5+5×1=55. Total resulting Forager contribution to gene pool: <10%. Once Neolithics dominate some regions, Foragers are a minority in their land even without wars and genocides (even though these last likely occurred). [agree, Razib]

3. Foragers don’t invent or adapt to agricultural lifestyles because they do not possess such changes and can’t develop them fast enough in most circumstances. They’re predisposed to fight or flee instead. Their much lower densities make them prone to high-density disease they didn’t evolve immunity to (but Neolithics did). [lean toward agreement, Razib]

4. Foragers thus get swamped by agriculturalists, and populations become dominated by the Neolithic Core Area population. Since mostly men migrate, in ever larger numbers, almost all Y-DNA is Neolithic; much of the mt-DNA is forager (since early women were taken from forager populations, and later women descend from these); but autossomes are overwhelmingly Neolithic too. [very slight lean toward agreement, Razib]

5. Established Neolithic populations live at the Malthusian limit. Extra food means extra surviving children eating it. [agree, Razib]

6. The only major changes in such a setting involve invasion by populations with food producing advantages. Like better seeds, tools (techs); better organization for irrigation works (culture); major genetic advantages like better digestion of food products (lactose tolerance). Advantageous alleles still diffuse, but neutral genes remain overwhelmingly local. [lean toward agreement, Razib]

7. “Invasions” and “Conquests” in such a setting are about militarized elites subjecting the peasants. Travelling is difficult and they are few compared to peasants. They live off rents collected from them, rather than join in the miserly peasant life. Since they despise peasants as serfs, they refer to themselves and their land by their minority identities. Thus we get “Roman” Tunisia; “Gothic” Ukraine; “Celtic” Anatolia, “British” Jamaica. This has no meaning as far as actual genetic constitution of the majority peasant population, but it’s all contemporary authors talk about, as well as most contemporary luxury works. [lean toward agreement, Razib]

8. If subjected populations live for long enough under the alien elite, they mix with it, appropriate their prestige tags, assimilate their prestige language with their substrate one, and much of material culture too. Thus French “Latins” with Celtic substrate, Bulgarian “Slavs”, Anatolian “Turks”, Egyptian “Arabs”, etc. Elites do make a contribution on Y-DNA, since their societies transmit prestige patriarchally. But almost no mt-DNA. And little autosomal DNA, since elite Y-DNA bearers persist but successive wives are mostly local. [lean toward agreement, Razib]

9. Slaves: slaves in settled agricultural societies do not have the impact they have in mostly unsettled Forager inhabited frontiers. Demographic success of agricultural slaves in the Americas is the exception not the rule for slave owning societies. Just like Agricultural minority success at Forager inhabited frontiers is the exception, and elite assimilation into settled populations the rule. African genes in the Americas expanded because they were able to join the early “Neolithic” gene pool there. They had high density disease immunity, agricultural knowledge, social and genetic adaptations, and the right crops versus Forager Amerindians in some regions. Slaves functioned as new rural “peasants” in untilled land from whom Barons extracted rents. [agree, Razib]

In Old World regions, where large peasant populations lived at the Malthusian limit, there was no advantage bringing slaves to till the land and replace the peasants. If a Baron could move the peasants from productive land so could he make them work as hard as slaves. Slaves were useful for house work, prestige, for city and mine labour. They had very severe social disadvantages. They generally died at far higher rates and reproduced a lot less than local peasants and so had to be continuously imported. They could not make large contributions to gene pools of very dense agricultural peoples, except if they carried food producing advantages, such as crops specially adapted to local circumstances. Slaves as a rule contribute a little mt-DNA, almost none Y-DNA and residual autossome DNA in such societies. [lean toward agreement, Razib]

10. Over time, once a functioning advanced agricultural community is established, no matter how many elite invasions and conquests, or how many slaves brought; there might be small but significant changes to Y-DNA and mt-DNA respectively. But autossomes are likely to remain the same, with only residual contribution (except if food producing improvements are brought by migrants as said). At least until such times when machines till the soil, people don’t live at the Malthusian limit, and they don’t continue to reproduce even though food available. [very slight lean toward agreement, Razib]

All this brings me to my final point. The closest analog to the “Ancestral South Indians” (ASI), who contribute ~45% of the ancestry of modern South Asians, are the native peoples of the Andaman Islanders (the period of divergence may be on the order of 20-30,000 years B.P.). The Andaman Islanders were obligate hunter-gatherers, and have a clear difficultly adapting to agricultural life. Were the ASI then hunter-gatherers assimilated by the “Ancestral North Indian” farmers? Diogenes says no. Rather, the survival of a substantial ASI element in the South Asian population is due, in his mind, to the fact that the ASI were themselves indigenous farmers. The analogy here then may be best made with the New World where agricultural indigenous populations in Mesoamerica and the highlands of South America were able to hold their own, and amalgamate with the Old World settlers, European and African. Greg Cochran recently said something similar as well, and the issue has been gnawing at me since First Farmers. I think I agree. My confidence is the proposition is very modest…but I have a difficult time understanding why ASI hunter-gatherers managed to contribute so much to the South Asian genome when related indigenous groups in Southeast Asia were so quickly marginalized by East Eurasian groups moving from the north.

(Republished from Discover/GNXP by permission of author or representative)
 
🔊 Listen RSS

The economist Samuel Bowles recently had a paper out in PNAS which caught my attention, Cultivation of cereals by the first farmers was not more productive than foraging. This naturally begs the question: why did farming conquer foraging as a lifestyle? First, let’s look at the abstract:

Did foragers become farmers because cultivation of crops was simply a better way to make a living? If so, what is arguably the greatest ever revolution in human livelihoods is readily explained. To answer the question, I estimate the caloric returns per hour of labor devoted to foraging wild species and cultivating the cereals exploited by the first farmers, using data on foragers and land-abundant hand-tool farmers in the ethnographic and historical record, as well as archaeological evidence. A convincing answer must account not only for the work of foraging and cultivation but also for storage, processing, and other indirect labor, and for the costs associated with the delayed nature of agricultural production and the greater exposure to risk of those whose livelihoods depended on a few cultivars rather than a larger number of wild species. Notwithstanding the considerable uncertainty to which these estimates inevitably are subject, the evidence is inconsistent with the hypothesis that the productivity of the first farmers exceeded that of early Holocene foragers. Social and demographic aspects of farming, rather than its productivity, may have been essential to its emergence and spread. Prominent among these aspects may have been the contribution of farming to population growth and to military prowess, both promoting the spread of farming as a livelihood.

My own working assumption is that the “first farmers” existed in a state of land surplus, and so like the medieval peasants in the wake of the Black Death found themselves released from Malthusian constraints, at least until their natural increase swallowed up their affluence. Bowles gives several reasons to be skeptical of this conjecture. The list in table 2 shows the positive and negative biases in the model when one back-projects later stages of farming to the initial period. Metal tools, well developed distribution channels, and more productive varieties, were features of mature agricultural societies. On the time-insensitive scale the necessity of planning ahead and waiting patiently for the crop to be ripe count against the gains of the farming way of life as well. The main variable which would weight in favor of farming is the land surplus alone, though Bowels argues that the ethnographic data as to the benefits of a surfeit of this input factor of production is mixed. I am skeptical of this point, though I can’t say I’ve dug deeply into the literature.

There are other factors, such as the fact that farmers were immobile, and so subject to attack. A shift toward a few crops also reduced the diversity of the diet, and therefore entailed a trade off between a diet rich in micronutrients, fiber, protein, and fat, to one overloaded on carbohydrates. Finally, a reliance on a few crops also means heightened “tail risk.” Think of the Irish potato blight. Hunter-gatherer populations would usually have a more diverse portfolio, and so be buffered more from environmental shocks.

One thing to add though is that the productivity of farming vs. foraging differs on the margin. Farming as a complement to foraging can be highly productive, as one substitutes labor hours devoted to low gain foraging to high gain farming. The key is that as farming comes to be the dominant strategy the low hanging fruit is picked, and one has to squeeze the same, or less, production out of a greater number of hours. So why farming and not foraging? I find Bowels conclusion rather cryptic:

However, an evolutionary argument may be able explain the eventual spread of farming once it was adopted in a few places. Because of extraordinary spatial and temporal variations in weather, soil quality, scarcity of wild species, and other conditions that could make farming rather than foraging an efficient provisioning strategy, it is likely that a few groups would have found it advantageous (by the marginal conditions above) to take up farming as their primary livelihood. Then, in order for farming subsequently to be adopted by other groups—the evolutionary problem—farming need not have lessened the toil of subsistence. Even if health status and stature declined, the lesser mobility of farmers would have lowered the costs of child rearing (41). This lowering could have contributed to the dramatic increase in population associated with cultivation (7) and, hence, to the spread of farming (12). Or the fact that agricultural wealth (stored goods and livestock particularly) was more subject to looting may have induced farming groups to invest more heavily in arms and to exploit their greater population densities, allowing them to encroach on and eventually replace neighboring groups (11).

I think this suggests is that farming vs. foraging is a tale of quantity vs. quality. But well mobilized quantity can be quality. The disciplined phalanxes of ancient Greece and the legions of Rome were those of peasant farmers. They may have been relatively lacking in meat and milk, and therefore muscle, in comparison to aristocratic Gaulish and Persian levies, but they made up for it in cohesiveness of collective action and singularity of political purpose. The static immobility and density of farmers may have made them more susceptible to the institutions and ideology which bind a society together, and so allowed a group of villages to operate almost as an organismic whole. Against this mass action the forager clans, effective as individual units, but unable to coordinate, may have been impotent.

Therefore, the rise of farming may have been accompanied by the first demagogues and the blitzkrieg.

(Republished from Discover/GNXP by permission of author or representative)
 
• Category: Science • Tags: Anthropology, Culture, Farming, Neolithic Revolution 
🔊 Listen RSS

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.

(Republished from Discover/GNXP by permission of author or representative)
 
🔊 Listen RSS

UE-1

When it comes to the synthesis of genetics and history we live an age of no definitive answers. L. L. Cavalli-Sforza’s Great Human Diasporas would come in for a major rewrite at this point. One of the areas which has been roiled the most within the past ten years has been the origin and propagation of the agricultural lifestyle across the European continent between 10,000-6,000 years before the present (starting in Europe’s southeast fringe a few thousand years after the origination of the Neolithic lifestyle in the Levant, and finally pushing into the southern Scandinavian peninsula only ~6,000 years ago). The reasons for this particular debate about the origin of the European are manifold. First, most scholars are of European ancestry, and some of the debates have roots going back a century. So a natural interest exists based on normal human biases. Second, when it comes to genetics the climate of Europe is ideal for the preservation and extraction of ancient DNA. Third, there are relatively clear and distinct theoretical models which can be tested by the data, whether to verify or refute.

ResearchBlogging.org I have already reviewed earlier work in three previous posts, European man perhaps a Middle Eastern farmer, European man perhaps not a Middle Eastern farmer, and Völkerwanderung back with a vengeance. Instead of rehashing everything I’ll take it as a given that you’ve read or skimmed those posts. Rather, let’s move on to a new paper in PLoS Biology, Ancient DNA from European Early Neolithic Farmers Reveals Their Near Eastern Affinities:

In Europe, the Neolithic transition (8,000–4,000 B.C.) from hunting and gathering to agricultural communities was one of the most important demographic events since the initial peopling of Europe by anatomically modern humans in the Upper Paleolithic (40,000 B.C.). However, the nature and speed of this transition is a matter of continuing scientific debate in archaeology, anthropology, and human population genetics. To date, inferences about the genetic make up of past populations have mostly been drawn from studies of modern-day Eurasian populations, but increasingly ancient DNA studies offer a direct view of the genetic past . We genetically characterized a population of the earliest farming culture in Central Europe, the Linear Pottery Culture (LBK; 5,500–4,900 calibrated B.C.) and used comprehensive phylogeographic and population genetic analyses to locate its origins within the broader Eurasian region, and to trace potential dispersal routes into Europe. We cloned and sequenced the mitochondrial hypervariable segment I and designed two powerful SNP multiplex PCR systems to generate new mitochondrial and Y-chromosomal data from 21 individuals from a complete LBK graveyard at Derenburg Meerenstieg II in Germany. These results considerably extend the available genetic dataset for the LBK (n = 42) and permit the first detailed genetic analysis of the earliest Neolithic culture in Central Europe (5,500–4,900 calibrated B.C.). We characterized the Neolithic mitochondrial DNA sequence diversity and geographical affinities of the early farmers using a large database of extant Western Eurasian populations (n = 23,394) and a wide range of population genetic analyses including shared haplotype analyses, principal component analyses, multidimensional scaling, geographic mapping of genetic distances, and Bayesian Serial Simcoal analyses. The results reveal that the LBK population shared an affinity with the modern-day Near East and Anatolia, supporting a major genetic input from this area during the advent of farming in Europe. However, the LBK population also showed unique genetic features including a clearly distinct distribution of mitochondrial haplogroup frequencies, confirming that major demographic events continued to take place in Europe after the early Neolithic.

sommer-nadachowski-2006-figAs I’ve indicated before the archaeological jargon is rather mystifying to me. Some of this is due to translation, the Linear Pottery Culture is abbreviated “LBK” because in the German it is Linearbandkeramik. Rather, I try and focus on some basic concrete parameters: time and space. So we have the first agricultural society with a focus on Central Europe flourishing ~7,000 years before the present. Some now we have the time and space in mind around which we can bracket all the background variables. The big question being asked, and answered, is whether the practitioners of LBK were descendants of Ice Age Europeans who expanded from the “refugia” in the south of Europe during the Last Glacial Maximum (LGM) ~20,000 years ago. To speak intelligently about these issues you need some basic intuition, so you see the map which I found on John Hawks’ weblog showing the line of settlement during the LGM. As the ice retreated presumably the European hunter-gatherers would have rapidly pushed northward, following the species which they consumed.

I’ll pass over the methodological nuts & bolts; you can find them in the paper. Obviously this isn’t technically trivial; extracting, amplifying, and avoiding contamination, from DNA samples on the order of 7,000 years old is awesome. As usual they focused on mtDNA because this is found in much larger quantities than nuclear DNA. They did get a few Y chromosomal results though, though mtDNA is the star of the show here. The mtDNA is the maternal lineage, so it can tell you only so much. Additionally, there may be selection dynamics going on to change the frequencies of some of these variants. But with those caveats in hand I think mtDNA patterns can be very informative because if women are on the move that is a pointer to a classic folk-wandering, where a whole people transplant their culture via migration. Many more British women arrived in the New World than Spanish women, and therein lay one of the crucial factors in the difference between Anglo and Latin America.

The slide show below has all the major figures of interest. I’ve also replicated the full description, and made some minor edits. Please take in the table; much of the paper really presupposes an intuitive familiarity with mtDNA haplogroup frequencies.


[zenphotopress album=214 sort=sort_order number=4]


mtDNA pairwise Fst by population
Hunter-Gatherers Near East LBK
Near East 4.46 * *
LBK 9.9 3.22 *
Central Europe 3.67 1 4.22

The authors also had an Fst table illustrating genetic distances using mtDNA of ancient and contemporary populations. I’ve cleaned up the table a bit, and standardized the values so that the smallest distance = 1. This is mostly so you can make immediate sense of it. What you clearly see is the enormous genetic distance between Central European hunter-gatherers and LBK, who were present in Germany right before the arrival of farmers. This comes very close to a falsification of the maximalist pots-not-people model, whereby farming spread from its point of origin in Anatolia and the Levant through a process of cultural diffusion, just like the alphabet or the potato. The relatively large distance between ancient and modern populations shouldn’t be too surprising, genetic distances operate across both time and space. There are interesting inferences one can make about the nature of gene flow over the past 10,000 years in Eurasia when viewing the relatively small distance between the two modern populations, but really the important point for the purposes of this paper is the high wall between the two cultures who practice differing modes of production.

In the paper the authors support, tentatively, a classic demic diffusion process. This is basically a very simple model whereby farmers with larger population growth rates expand into the “space” of hunter-gatherers. But as Dienekes Pontikos notes such a process would also be characterized by dilution of the original Middle Eastern “genetic signal” over time. Rather, what we see here seems to be a total transfer for a population across large distances. The authors themselves note that the LBK farmers seem to have followed the interior lines of rivers and flat-bottom plains. Farmers had discovered a new way to exploit nature, but in the end they were still ecologically constrained. The northern two-thirds of Scandinavia still had hunter-gatherer populations down to the period of the classical Greeks. This was not because of the powerful magic wielded by Väinämöinen. The Middle Eastern derived agricultural toolkit no doubt began to run into its natural ecological limits on Europe’s northern fringe. Without knowing anything further I suspect that the death of the southern Sami culture in the face of Norwegian and Swedish expansion in the early modern period was probably driven by the emergence of more systematic agricultural science, which could push the ecological limits beyond the long-standing equilibrium established in the Iron Age.

But I don’t think this is just a story of ecology. It is clearly a story of culture. We assume that culture is easily transferable from society to society. In some ways it is. The original phonetic script of Upper Mesopotamia and Syria seems to have quickly triggered imitation and appropriation from India to Italy within a few centuries of its widespread use by the Aramaeans. But farming is not like the idea of writing. The original farmers seem to have expanded rather slowly initially out of the Middle East. Not only did they perfect the biological character of their crops, they probably perfected the customs and traditions which would go along with farming. A complex suite of explicit rules and implicit norms. Perhaps it was not so easy to simply copy the farming lifestyle? Or, perhaps more interestingly, the hunter-gatherers by and large did not want to copy the farming lifestyle? (this is a tendency among some modern non-farming groups, who would rather work temporarily on farms themselves rather than become full-time obligate peasants) The large genetic distances between the LBK and the hunter-gatherers around them may indicate not only the relatively endogenous growth of the LBK in “virgin” land (e.g., compare to the Yankees of New England in the 17th and 18th century), but, also the emergence of an ideological aversion to mixing with the “savages.” We have plenty of textually attested de-humanization of the “savage” and “barbarian” by the “civilized.” It is likely that the gap between the LBK and the hunter-gatherers of Europe was only somewhat smaller than that between the Aborigines of Australia and Tasmania and the European settlers!

Finally, there’s one last issue I want to highlight: the authors find that many presumably hunter-gatherer lineages are found among the LBK, while very common haplogroups (mtDNA and Y) in Europe today are not found among the LBK or the ancient hunter-gatherers. The clear inference then would be that Europe went through several periods of demographic change and migration within the last 10,000 years. A simple two-way admixture scenario will not suffice. Yesterday I posted this bar plot which contrasted the pattern of ancestry of French vs. French Basque using ADMIXTURE at K = 10:

French

The green element is nearly 100% in Sardinia, and drops off to nearly nothing somewhere around Iran. The light blue component is modal around the Caucasus, though is widely distributed, from Spain to Bengal (yeah, that’s me!) to Sweden. A simple model would be that the light blue arrived with Neolithic agriculturalists, as the Basques are the descendants of the original Ice Age Europeans. But this may not be correct, and our impression of the Basques may be totally false. It is not out of the question now that the Basque culture may have arrived via the ancient leap-frogging of agriculture from fertile regions around the Mediterranean before the seafarers passed into the Atlantic and swept around the western fringe of Iberia. What we may be seeing is a palimpsest of agriculturalists, where the Basques simply lack the last layer.

In any case, one can speculate a lot right. Ancient DNA has allowed us to refute maximalist versions of pots-not-people, but has also overturned our ability to hold to simple robust models. In science you prefer parsimony, unless parsimony simply can’t explain the patterns at hand. I think we’re there at this point.

Citation: Wolfgang Haak, Oleg Balanovsky, Juan J. Sanchez, Sergey Koshel, Valery Zaporozhchenko, Christina J. Adler, Clio S. I. Der Sarkissian, Guido Brandt, Carolin Schwarz, Nicole Nicklisch, Veit Dresely, Barbara Fritsch, Elena Balanovska, Richard Villems, Harald Meller, Kurt W. Alt, Alan Cooper, & Genographic Consortium (2010). Ancient DNA from European Early Neolithic Farmers Reveals Their Near Eastern Affinities PLoS Biology : 10.1371/journal.pbio.1000536

(Republished from Discover/GNXP by permission of author or representative)
 
🔊 Listen RSS

1400062152 The cockroach as we know it has been around for ~140 million years. That’s a rather long run. The evolutionary design of the cockroach seems to be well suited to avoiding obsolescence; it’s withstood the test of time. I suspect that the particular example of the roach is often used to illustrate the blindness of evolution because of its lack of aesthetic alignment with the the values of modern humanity. Unlike the elegant wasp or the industrious bee the cockroach seems to have few redeeming characteristics on first blush. The Hutus referred to the Tutsis as cockroaches before and during the Rwanda genocide of 1994. And yet the roach succeeds, it breeds, and it flourishes.

Some of the same class of issues pertain to our own species. What we feel to be edifying, to be aesthetically pleasing, may not comport with the final judgement of history, of evolution. The narrative of man ascending which has become so popular since the Enlightenment turns out to present us with some problems when one realizes that our species seems to have regressed on particularly transparent metrics such as height and cranial capacity since the last Ice Age. But the prevailing wisdom of the ancients that we descend from an Edenic Golden Age also does not seem to necessarily comport with the record at hand either. Just as the past is cloudier than we once perceived it to be, so the future often looks muddled from the perspective of the present. How did man come to be? What should we be? And why should we be? These are a combination of positive and normative questions, and Spencer Wells tackles them in his newest book, Pandora’s Seed: The Unforeseen Cost of Civilization.

Wells is a relatively prominent public intellectual. He came to the fore in the early aughts with his book The Journey of Man: A Genetic Odyssey, which was made into a documentary of the same name, and led to Wells heading National Geographic‘s Genographic Project. A geneticist by training the history of the human species has always been one of his passions, and that topic has become the current focus of his career. But while The Journey of Man was a historically inflected work of genetics, Pandora’s Seed is a scientifically inflected work of history; political, social, and economic. There are broad family similarities to Jared Diamond’s Guns, Germs, and Steel, but Pandora’s Seed is both more tightly written and broader in scope. Wells describes the past, posits some tentative predictions about the future, assesses the present, and questions whether we need to reclaim a firmer and clearer grasp of the aims of the well lived life.

logscalpopThe first third of the book is focused on the Neolithic Revolution. Or perhaps more accurately the agricultural innovation. In its broad outlines I agree with Wells’ thesis that the transition to an agricultural lifestyle resulted in greater morbidity because of the shift away from a diversified diet to one based on grains. With the judicious use of charts and illustrations Pandora’s Seed outlines how pre-agricultural sedentarists of the post-Ice Age Natufian culture had to adopt the conscious planting and harvesting of grain due to a change in their environment. That change was the exogenous shock of the Younger Dryas, which saw a reversion back to dryer and colder conditions. The model of adaptation in the face of inclement conditions is persuasive precisely because it so human. In extreme circumstances human populations set in their ways must abandon tried & true traditions which are found wanting and explore the space of possibilities so as to maintain their viability. This ingenuity in the face of resource exhaustion or scarcity has occurred many times in human history. The critical factor distinguishing the present from the past is not the reality of innovation itself, but the rate of innovation.

But at this point I must enter into the record a major caveat, and even object to the veracity, of the story which unfolds in Pandora’s Seed. I will quote the section which raised my eyebrows in full:

…As the land dried out, the wild grain retreated from the lowlands, remaining only in the higher mountain valleys, where it could get enough water. The Natufians had to travel farther and farther from their lowland settlements to gather enough to survive. This would have put tremendous pressure on food supply, and probably esulted in an increased mortality rate in these people accustomed to a land of plenty. It was humanity’s first real encounter with Thomas Malthus’s conjecture that popualtion growth will eventually produce more people than can be supproted by the availalble food supply.

CARRYSpencer Wells has a doctorate in biology, and great breadth of knowledge. So perhaps there is some detail or nuance I’m missing here, but the fact is that all organisms are subject to Malthusian laws except in the transient state of resource surplus. The term “carrying capacity” is one which one learns in introductory biology courses for a reason. The hunter-gatherers no doubt pushed up against their carrying capacity. I am aware of arguments that weaning and infanticide constrained hunter-gatherer populations, but even granting such forethought would not abolish the vicissitudes of exogenous disruptions in climate and ecosystem. Even the most culturally anti-natalist tribe would at some point be faced with a situation where circumstances outside of their control would leave the adults above the Malthusian limit of their local territory. Wells argues that for much of human history we were expanding in a transient. But this does not negate the broader point that animals generally move up to the carrying capacity of the local ecosystem rather quickly because of the nature of natural increase. In the course of history exogenous shocks generally produce periodic culls of the herd. Spencer Wells implicitly endorses this reality by his tacit support for the Toba catastrophe theory.

Many of the other arguments which implicitly argue for the superiority of the hunter-gatherer mode of production over the agricultural one are somewhat tendentious, but in those cases Wells usually presents the “other side.” For example he is skeptical from what I can tell of the idea of widespread organized war among hunter-gatherers, but he grants evidence of relatively high mortality rates due to conflicts of a more limited scale, but still significant when judged against the small sizes of the ancient bands. The main big picture reality seems to be that hunter-gatherers were generalists with few material goods. The world of The Gods Must Be Crazy was no utopia, but it illustrated how physical objects of value and scarcity could introduce conflict and tension, above and beyond the mundane realities of human existence (also see The Pearl).

800px-David_-_The_Death_of_SocratesMuch of the second half of Pandora’s Seed leaps forward from the Stone Age to the present, and attempts to grapple with the reality that many of our competencies are not much advanced over that of the hunter-gatherer despite the fact that we are embedded in a world of extreme sophistication and specialization. I’m reminded of the old 1990s hit Mo Money, Mo Problems. Over the past 10,000 years our species has ascended up an irreversible ratchet of population density, complexification of society, and specialization of labor. And for what? In some ways Pandora’s Seed presents a profoundly pessimistic case, and verges on being a 21st century update of the idealizations of the Romantics of savage peoples who lived in enchanted worlds without worry. The title of the book seems justified.

But then he asks a real question: why? Why to be, as opposed to not to be? With the rise of mass agricultural society such questions were answered definitively by philosopher shamans. At least in their own minds. In China they were called Sages, in India Rishis, and in the West the philosophers, prophets, and Church Fathers. The names may have differed, but this specialized caste spoke and wrote, and the other rentier castes listened and gave nominal fealty to the theories propounded. Over the last few centuries this old world of certainty has collapsed, and a cacophony of voices have arisen, over which looms an operational nihilism. The consumer society which is the apotheosis of “development” is characterized by an all-you-can-eat buffet of gadgets, sensations, and social signalers. Even the religious philosophies which theoretically stood opposed to this sort of gluttony have in part been absorbed or co-opted. Spencer Wells does not come to any conclusion that I can see to resolve this existential Gordian Knot. But a serious conversation needs to be started amongst those of us who no longer bow to the gods, the cosmos, or the ancients. It must be remembered that in some versions of the myth of Pandora hope remains within the jar which she opened.

(Republished from Discover/GNXP by permission of author or representative)
 
No Items Found
Razib Khan
About Razib Khan

"I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. If you want to know more, see the links at http://www.razib.com"