Chapple, R. M. 2012 'Booms and Busts in Europe’s Earliest Farming Societies- Review' Blogspot post
Booms and Busts in Europe’s Earliest Farming Societies: Review Originally posted online on 21 February 2012 at rmchapple.blogspot.com (http://rmchapple.blogspot.co.uk/2012/02/booms-and-busts-in-europes-earliest.html)The PCC Lunchtime Seminar Series is run by the School of Geography, Archaeology andPalaeoecology at QUB in Belfast. I believe that they have been going for some time nowand, although I’ve regularly been told about them and how I really should get alongthere, I’ve somehow not managed to make it. However, I promised myself that the nextopportunity I got I would definitely attend – come hell or high water. I spoke to a friendof mine who told me that the next one coming up (Tuesday 21st February 2012) was onEarly Neolithic Farming. I liked the sound of that and I promised faithfully that I wouldbe there. It only occurred to me the day before the lecture to enquire who the speakerwas. When I was told that the speaker would be Prof. Stephen Shennan my heart justfell. I have nothing against the man, I truly don’t. Prof. Shennan is Director of the UCLInstitute of Archaeology. He is also Professor of Theoretical Archaeology, and Fellow ofthe British Academy. As I found out when I spoke to him after the lecture, he is a trulyaffable person with a ready smile and keen sense of humour. Nonetheless, for me hisname is eternally associated with that part of my life, during the mid to late 90s, when Iwas embroiled in writing my MA thesis [also available: here]. I was working on astatistical and morphological approach to the ringforts of the Loop Head Peninsula inCo. Clare and Shennan’s book, Quantifying Archaeology, was my constant companion.There were certain sections of my thesis that relied so much on his work that I wasafraid of being dismissed for plagiarism. I even had dreams about repeatedly typing‘Shennan (1988) says/states/argues’ etc. By the time I completed my thesis, my copyof Quantifying Archaeology was in such a poor state it had to be held together withrubber bands. Yes, I was slightly terrified at being in the room with this man.
As it turned out there was no need to be. He began by outlining some concepts ofEvolutionary Demography Theory. The concept is that for people in past societies,producing children were not so much a means to an end, but a good in their own right.There are also a number of trade-offs implicit in having children, not least of which isthe number of children it is possible to bear, but how many of one’s offspring canfeasibly survive to sexual maturity and become parents themselves. Changingenvironmental and technological conditions can thus alter the balance of these trade-offs, resulting in increased or decreased fertility. To illustrate this, Shennan showed agraph comparing the ages of women giving birth for the first time in a modern Mayancommunity and how the demographics changed after the introduction of electric pumpsto supply water. In the pre-electric pump society around 50% of the women had givenbirth to their first child by the age of 21. However, the addition of the electric pumpsallowed women to be freed from the drudgery of water carrying and resulted in anincreased carrying-capacity for the society. In the latter situation almost 75% of womenhad had their first child by the age of 21. Shennan was quick to point out that thedecisions to have children, what numbers, and at what time, are carried out a householdlevel, but have large-scale population-level results. Thus, there are demographicconsequences in acquitting a new adaptations and technologies, such as cereal- andpulse-based agriculture. Where we find evidence for population stability, it may betaken as evidence that a local carrying-capacity ceiling had been reached. Shennan seesthe spread of farming in the Neolithic as a classic example of a dispersal opportunityacquired through greater technological achievement. There is also the fact that this formof agriculture is extremely portable – seed and livestock may be moved with relativeease. Shennan argues that this all leads to a significant increase in environmentalcarrying capacity that results in both increased fertility and eventual population growth.He argues that, contrary to some theories of the spread of agriculture, this is not apopulation ‘push’ process but a biological ‘pull’ process. This means that it is not asituation where an increased population is forced to develop more effective means offeeding itself (thus adopting agriculture). Instead, this model is one where thepopulation acquires agricultural skills and then discovers that it can support more andlarger families, leading to a population growth.Shennan noted that while there is much in the published literature about the earliestbeginnings of agriculture, many researchers appear to assume that once it is in place,
there is little to be interested in. However, in examining the evidence from easternFrance, the data shows a sequence of population expansions, interspersed with welldefined gaps where the population contracts (Peterquin et al. 1996). For example,Zimmerman’s (2009) analysis of Neolithic Bandkeramik sites in the lower Rhine basin.Here there is evidence for population growth at the beginning of the Neolithic, around5300 cal BC. There then appears to be continued growth for over a century, followed bysevere population contractions by around 4900 cal BC. To test these hypotheses,Shennan and his team (Sean Downey, Adrian Thompson, Kevan Edinborough & MarkThomas) used summed radiocarbon date distributions as a proxy for the relativeamount of population activity. This approach was then used to compare data from thepollen record with radiocarbon dates from across the UK. The methodology involvedconverting the pollen spectrum into ‘Land Clearance Category Reconstructions’ plottedagainst the summed and normalised, geo-referenced, radiocarbon dates. This was allthen divided up into bins of 250 years. The available data runs from 9000 cal BP toaround 3600 cal BP. The UK evidence shows an inferred population growth (whatShennan terms an ‘upward blip’) around 7600 cal BP. This is paralleled with a‘downward blip’ in the amount of deciduous woodland. Essentially, the arrival offarming is shown to result in an increase in the population, coupled with a decrease inwoodland. At around 5300/5200 cal BP there is an observable drop in population thatcontinues to after c. 4500 cal BP. After this point there is an increase in deciduouswoodland and (unexpectedly) an increase in semi-open pasture. Again, around 4400 calBP there is a decrease in woodland and a corresponding increase in semi-open pasturethat is taken to suggest an increase in population. One of the interesting conclusions tobe drawn from this analysis is that it suggests that what we are witnessing isanthropogenic change to the environment – as opposed to climate change being theprimary determining factor. To test the robustness of these dates and this methodologythe dates were segregated by type. In this way dates from cereal grains could beseparated from dates associated with upstanding monuments. In theory, if there is agenuine underlying trend in population growth, it should be mirrored by both sets ofdata independently. Certainly, this has been demonstrated to be the case during theearlier Neolithic, but there is a marked divergence in the patterns during the LateNeolithic, from around 4000 cal BP.This model was then recreated for ten different regions in Western Europe. Within eachof these regional studies, Shennan and his team took 1000 dates as a ‘bootstrap sample’to model variation. For example, in the Scottish study there were 305 dated site phases.Here there is an observable population boom around 5500 cal BP. In Ireland, with 1031dated site phases, there is a similar population boom at around 5500 cal BP, followed bya trough around 5000 cal BP. A further rise in population may be noted around theperiod 5000-4000 cal BP. In Germany, where farming was introduced approximately1500 years before it reached Ireland, the Bavaria-Baden-Wurttemberg study area showspeaks at 7000 cal BP, 5500 cal BP and 4600 cal BP. There are also intervening troughsin population centred on 6200 cal BP and from 5200 cal BP to 5000 cal BP. Similarregional studies were carried out for the Low Countries (347 dated site phases), theParis Basin (188 dated site phases), and the Rhone-Languedoc (340 dated site phases)areas (among others). In all of theses the general pattern of population booms and bustsis repeated over and over.
Shennan then posed the question: are these patterns real? The fact that the radiocarbondata largely mirrors the pollen data suggests that, yes, they are real. However, there isstill the possibility that these patterns are spurious and are merely the result ofanomalies within the calibration curve or have appeared as the results of samplingerrors etc. To counter such arguments, the team devised a set of statistical tests. AsShennan said, these are quite technical and difficult to take in. If I have understood himcorrectly, the test centred on simulating 50,000 randomly generated radiocarbon dates,spread across the time-period under discussion and broken up into 10 year bins. Thesewere then assigned error ranges that mimicked the real distribution of the calibrationcurve and the standard deviations of genuine radiocarbon dates. Essentially, theyrecreated 50,000 simulated radiocarbon dates with the same level ofprecision/imprecision (or ‘fuzziness’) as one would expect from real dates. Added to thisthey factored in the known levels of population growth and taphonomic decay (thatthere is less probability of materials surviving from earlier vs. later contexts). Together,this model predicts an exponential growth of data (and population) over time. When thesimulated data is compared to the real evidence some clear patterns of higher and lowerthan predicted activity are revealed. This means that the results may be interpreted asbeing a true reflection of genuine population trends within the data and not merelyartefacts of the data itself. In the Wessex-Sussex and Irish regional studies the samepatterns as before are noted, with rising population booms being followed by busts. Theresults are less marked for other regions, such as central Germany and southern France,though this appears to be due to their smaller sample sizes available for study. Shennanand his colleagues have been able to conclude that the pattern of boom and bust areclear and genuine occurrences.A further question was asked – could there be any correlations between these resultsand climate patterns? The idea was that the results may still have been spurious andthat the data was not indicating parallels between demography and climate, but merelyreflecting the level of 14C in the atmosphere. The team used two climate proxies:the NGRIP and the Crag Cave, Co. Kerry, δ18O data. Again, a series of statistical testswere devised to eliminate all possible bias within the data. With the exception of theregional study of the Low Countries, no statistically significant correlation was foundbetween the two sources. This again demonstrates the robustness of the data and thepopulation expansion and contraction patterns already observed.Finally, Shennan examined a number of other studies to compare their results with hisown. Similarities were noted with dates from flint mining in Britain (Kerig et al. inpress) which shows a marked rise in dates around 4000 cal BC with a major fall-off andminor peaks after that time. Parallels were also found in the dates associated withcausewayed enclosures (this comparison was carried out before the publicationof Gathering Time). In his concluding remarks, Shennan admitted that, in manyrespects, it is predictable that people would take reproductive advantage of theintroduction of new technology that improved their lifestyles. However, there are, as yet,no firm reasons as to what caused these cycles of boom and bust. He argues that futureresearch must take into account the demographic history of populations both as a causeand as an effect of the process. Even with all these ideas in mind, it is still likely that the
socio-economic processes that drove these cycles were different for the growth anddecline phases. Essentially, the appearance of agriculture may be associated with theinitial population booms observed in the various study areas, but the probable reasonsfor the declines are much more obscure.Note:I hope that I have done justice to Prof. Shennan’s lecture and managed to convey at leastthe gist of his ideas and results. Nonetheless, I do sincerely apologise if, in the rush towrite notes and keep up with the pace of delivery, I have misrepresented or misquotedthe speaker. If so, please feel free to contact me, and I will endeavour to set the recordstraight.If you’re going to do any shopping through Amazon, please go via the portal below. Itcosts you nothing, but it will generate a little bit of advertising revenue for this site! I have not been able to give the full references to any of the literature referenced inthe lecture – sorry.