The Origin and Evolution of Cultures (IV)

“The first half of the book was not easy to read due to the technical nature of the coverage, and so I decided to put it away for a while. However I did pick it up again, and I’m really glad I did as there’s simply no way around the fact that this book is awesome. Some of the chapters in this book are chapters you need to read.

Highly recommended. Probably the best book I’ve read this year.”

I’ve finished the book – the above is my review of it on goodreads. I gave the book five stars.

The last part of it had (at least) two of those must-read chapters which I when I read them feel like I really ought to blog, and they both had a lot of stuff. The first of these chapters was an awesome chapter on agriculture. I wrote some stuff of my own about that stuff in my last post about the book (I’ve incidentally corrected a few minor inaccuracies in that post since it was posted – I thought I should mention this here), but I’m pretty sure I wouldn’t have done this if I’d known what was in that chapter; they cover this topic in a lot of detail and they do it really well. Many of the aspects they cover incidentally do not overlap with what I wrote though some of course do; you’ll surely get a lot out of reading this post despite having read my earlier comments on the topic (at least if you’re interested in these sorts of things). In my archaeology textbook, which is only a few years old, the idea that the dramatic climate change which took place around the Pleistocene/Holocene boundary was a crucial factor in the development of agriculture is taken for granted, but Boyd and Richerson’s coverage reminds us that archaeologists were not always so eager to accept this hypothesis (and it should be noted that other, weaker, hypotheses are mentioned/covered in the archaeology text as well – I was skeptical about some of these while reading the book (I wrote a couple of pretty harsh remarks in the margin) because they seemed implausible to me; Boyd and Richerson illustrates in the chapter e.g. through application of models of population dynamics that I had reason to be skeptical). I forgot to talk about climate in my last post on the topic probably because I assumed people knew this part, but it gets its fair share of the attention in this post anyway so I guess no harm is done.

The other chapter I consider to be best categorized as a ‘must-read’ chapter is chapter 19, on ‘Simple Models of Complex Phenomena’, which relates a little bit – but only a little – to a blog post of mine which has recently got some attention. When reading that chapter I was never in any doubt I’d cover that stuff here – this stuff is pure gold. The ‘Microevolutionary processes give rise to history’-chapter was also really interesting and the last chapter on memes there are probably more than a few people who’d benefit from reading, but I’ll not cover that stuff here; I don’t think I’d have problems writing 4 or 5 posts about the remaining parts of the book, and this is simply too much. I’ll talk about agriculture in this post and then I’ll probably cover the model chapter in a later post. It’s possible that the agriculture coverage in the book is less interesting to people with very limited knowledge of archaeology and human prehistory than it is to me (not that I’d say I know much about this stuff – actually on second thought I probably belong in the group of people with ‘very limited knowledge’ as well…), because a lot of things which relate closely to what they write about are perhaps hard to conceptualize without knowing anything about these things, but anyway I write about what I find interesting, so here we are.

Let’s move on to the book chapter coverage:

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“Numerous subsequent investigations [after the Braidwood team] now provide a reasonably detailed picture of the origins of agriculture in several independent centers and its subsequent diffusion to almost all of the earth suitable for cultivation. These investigations have discovered no region in which agriculture developed earlier or faster than in the Near East, though a North Chinese center of domestication of millet may prove almost as early. Other centers seem to have developed later, or more slowly, or with a different sequence of stages, or all three. The spread of agriculture from centers of origin to more remote areas is well documented for Europe and North America [a major problem in relation to East Asia/China is incidentally the lack of ‘transitional sites’ dated around 8.000 to 6.000 years BC; we have very early sites and then we have “abundant and widespread evidence for sedentary Neolithic villages” by 6000 BC (Scarre et al.) – but we miss some evidence as to what happened in between – US]. Ethnography also gives us cases where hunters and gatherers persisted to recent times in areas seemingly highly suitable for agriculture, most notably much of western North America and Australia. Attempts to account for this rather complex pattern are a major focus of archaeology.”

“The processes involved in such a complex phenomenon as the origin of agriculture are many and densely entangled. Many authors have given climate change a key explanatory role […] The coevolution of human subsistence strategies and plant and animal domesticates must also play an important role […] Hunting-and-gathering subsistence may normally be a superior strategy to incipient agriculture […], and, if so, some local factor may be necessary to provide the initial impetus to heavier use of relatively low-quality, high-processing-effort plant resources that eventually result in plant domestication. Population pressure is perhaps the most popular candidate […] Quite plausibly, the complex details of local history entirely determine the evolutionary sequence leading to the origin and spread of agriculture in every region. Indeed, important advances in our understanding of the origins of agriculture have resulted from pursuit of the historical details of particular cases […] Nonetheless, we propose that much about the origin of agriculture can be understood in terms of two propositions:
Agriculture was impossible during the last glacial age. During the last glacial age, climates were variable and very dry over large areas. Atmospheric levels of CO2 were low. Probably most important, last-glacial climates were characterized by high-amplitude fluctuations on timescales of a decade or less to a millennium. Because agricultural subsistence systems are vulnerable to weather extremes, and because the cultural evolution of subsistence systems making heavy, specialized use of plant resources occurs relatively slowly, agriculture could not evolve.
In the long run, agriculture is compulsory in the holocene epoch. In contrast to the Pleistocene climates, stable Holocene climates allowed the evolution of agriculture in vast areas with relatively warm, wet climates, or access to irrigation. Prehistoric populations tended to grow rapidly to the carrying capacity set by the environment and the efficiency of the prevailing subsistence system. Local communities that discover or acquire more intensive subsistence strategies will increase in number and exert competitive pressure on smaller populations with less intensive strategies. Thus, in the Holocene epoch, such intergroup competition generated a competitive ratchet favoring the origin and diffusion of agriculture.”

This is the basic idea. But the chapter has a lot more:

“For the last 400,000 years, very high-resolution climate proxy data are available from ice cores taken from the deep ice sheets of Greenland and Antarctica. Resolution of events lasting little more than a decade is possible in Greenland ice 80,000 years old, improving to monthly resolution 3,000 years ago. During the last glacial, the ice core data show that the climate was highly variable on time scales of centuries to millennia […] The last glacial period was arid and extremely variable compared to the Holocene. Sharp millennial-scale excursions occur in estimated temperatures, atmospheric dust, and greenhouse gases. The intense variability of the last glacial carries right down to the limits of the nearly 10-year resolution of the ice core data. […] Even though diffusion and thinning within the ice core progressively erases high-frequency variation in the core […] the shift from full glacial conditions about 18,000 years ago to the Holocene interglacial is accompanied by a dramatic reduction in variation on timescales shorter than 150 years. The Holocene (the last relatively warm, ice-free 11,600 years) has been a period of very stable climate, at least by the standards of the last glacial age.[2] The climate fluctuations recorded in high-latitude ice cores are also recorded at latitudes where agriculture occurs today. Sediments overlain by anoxic water that inhibits sediment mixing by burrowing organisms are a source of low- and mid-latitude data with a resolution rivaling ice cores. Events recorded in North Atlantic sediment cores are closely coupled to those recorded in Greenland ice […], but so are records distant from Greenland. Hendy and Kennett (2000) report on water temperature proxies from sediment cores from the often-anoxic Santa Barbara Basin just offshore of central California. This data shows millennial- and submillennial-scale temperature fluctuations from 60–18 thousand years ago with an amplitude of about 8°C, compared to fluctuations of about 2°C in the Holocene epoch. As in the Greenland cores, the millennial-scale events often show very abrupt onsets and terminations and are often punctuated by brief spikes of warmth and cold.”

“We expect that opportunism was the most important strategy for managing the risks associated with plant foods during the last glacial age. Annual plants have dormant seed that spreads their risk of failure over many years, and perennials vary seed output or storage organ size substantially between years as weather dictates. In a highly variable climate, the specialization of exploitation on one or a few especially promising species would be highly unlikely, because ‘‘promise’’ in one year or even for a decade or two would turn to runs of years with little or no success. However, most years would likely be favorable for some species or another, so generalized plant-exploitation systems are compatible with highly variable climates. […] Plant food-rich diets take considerable time to develop. Plant foods are generally low in protein and often high in toxins. Some time is required to work out a balanced diet rich in plant foods, for example, by incorporating legumes to replace part of the meat in diets. Whether intensification and agriculture always lead to health declines due to nutritional inadequacy is debatable, but the potential for them to do so absent sometimes-subtle adaptations is clear […] The seasonal round of activities has to be much modified, and women’s customary activities have to be given more prominence relative to men’s hunting. Changes in social organization either by evolution in situ or by borrowing tend to be slow […] We doubt that even sophisticated last-glacial hunter-gatherers would have been able to solve the complex nutritional and scheduling problems associated with a plant-rich diet while coping with unpredictable high-amplitude change on timescales shorter than the equilibration time of plant migrations and shorter than actual Holocene trajectories of intensification.”

“Low mean productivity, along with greater variance in productivity, would have greatly decreased the attractiveness of plant resources during the last glacial age. Lower average rainfall and carbon dioxide during the last glacial age reduced the area of the earth’s surface suitable for agriculture […] On present evidence we cannot determine whether aridity, low CO2 levels, millennial-scale climate variability, or submillennial-scale weather variation was the main culprit in preventing the evolution of agriculture. Low CO2 and climate variation would handicap the evolution of dependence on plant foods everywhere and were surely more significant than behavioral or technological obstacles. Hominids evolved as plant-using omnivores (Milton, 2000), and the basic technology for plant exploitation existed at least 10 thousand years before the Holocene […] At least in favorable localities, appreciable use seems to have been made of plant foods, including large-seeded grasses, well back into the Pleistocene […] Significantly, we believe, the use of such technology over spans of last-glacial time that were sufficient for successive waves of intensification of subsistence in the Holocene led to only minor subsistence intensification, compared to the Mesolithic, Neolithic, and their ever-more-intensive successors. […] After 11,600 B.P., the Holocene period of relatively warm, wet, stable, CO2-rich environments began. Subsistence intensification and eventually agriculture followed. Thus, while not perfectly instantaneous, the shift from glacial to Holocene climates was a very large change and took place much more rapidly than cultural evolution could track.”

“Might we not expect agriculture to have emerged in the last interglacial 130,000 years ago or even during one of the even older interglacials? No archaeological evidence has come to light suggesting the presence of technologies that might be expected to accompany forays into intensive plant collecting or agriculture at this time. Anatomically modern humans may have appeared in Africa as early as 130,000 years ago […], but they were not behaviorally modern. Humans of the last interglacial were uniformly archaic in behavior. Very likely, then, the humans of the last interglacial were neither cognitively nor culturally capable of evolving agricultural subsistence. However, climate might also explain the lack of marked subsistence intensification during previous interglacials. Ice cores from the thick Antarctic ice cap at Vostok show that each of the last four interglacials over the last 420,000 years was characterized by a short, sharp peak of warmth, rather than the 11,600-year-long stable plateau of the Holocene (Petit et al., 1999).”

“Once a more productive subsistence system is possible, it will, over the long run, replace the less-productive subsistence system that preceded it. The reason is simple: all else being equal, any group that can use a tract of land more efficiently will be able to evict residents that use it less efficiently […] More productive uses support higher population densities, or more wealth per capita, or both. An agricultural frontier will tend to expand at the expense of hunter-gatherers as rising population densities on the farming side of the frontier motivate pioneers to invest in acquiring land from less-efficient users. […] Thus, subsistence improvement generates a competitive ratchet as successively more land-efficient subsistence systems lead to population growth and labor intensification. Locally, huntergatherers may win some battles (e.g., in the Great Basin; Madsen, 1994), but in the long run the more intensive strategies will win wherever environments are suitable for their deployment. The archaeology supports this argument […] Societies in all regions of the world undergo a very similar pattern of subsistence efficiency increase and population increase in the Holocene, albeit at very different rates. Holocene hunter-gatherers developed local equilibria that, while sometimes lasting for thousands of years, were almost always replaced by more intensive equilibria.”

“Cohen’s (1977) influential book argued that slowly accumulating global-scale population pressure was responsible for the eventual origins of agriculture beginning at the 11,600 B.P. time horizon. He imagines, quite plausibly, that subsistence innovation is driven by increases in population density, but, implausibly we believe, that a long, slow buildup of population gradually drove people to intensify subsistence systems to relieve shortages caused by population growth, eventually triggering a move to domesticates. Looked at one way, population pressure is just the population growth part of the competitive ratchet. However, this argument fails to explain why pre-agricultural hunter-gatherer intensification and the transition to agriculture began in numerous locations after 11,600 years ago […] Assuming that humans were essentially modern by the Upper Paleolithic, they would have had 30,000 years to build up a population necessary to generate pressures for intensification. Given any reasonable estimate of the human intrinsic rate of natural increase under hunting-and-gathering conditions (somewhat less than 1% yr^-1 to 3% yr^-1, populations substantially below carrying capacity will double in a century or less […] If agricultural technologies were quick and easy to develop, the population pressure argument would lead us to expect Pleistocene populations to shift in and out of agriculture and other intensive strategies as they find themselves in subsistence crises due to environmental deterioration or in periods of plenty due to amelioration. Most likely, minor intensifications and de-intensifications were standard operating procedure in the Pleistocene. However, the time needed to progress much toward plant-rich strategies was greater than the fluctuating climate allowed, especially given CO2- and aridity-limited plant production.”

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This part is really important to understand, and I know I’ve talked about this before but I’ll say it again: Humans living, say, 25.000 years ago were not stupid. They weren’t monkeys walking around looking for berries in the woods. They probably tried and tried repeatedly to make this kind of stuff work, explore all kinds of creative ways to obtain enough/more food, always slightly adjusting their strategies in order to stay alive and keep having kids – but the climate wouldn’t allow them to ever achieve ‘take off’. As they put it towards the end of the chapter: “If climate variation did not limit intensification during the last glacial age to vanishingly slow rates compared to the Holocene epoch, the failure of intensive systems to evolve during the tens of millennia anatomically and culturally modern humans lived as sophisticated hunter-gatherers before the Holocene is a considerable mystery.” It seems climate is a big part of the explanation why we never got to where we are now before we did. Environmental constraints limit the activities of all lifeforms in all kinds of ways, and it would serve us well every once in a while to recall that we are in fact no different, even if we like to think we are, and that such effects may have played a crucial role in the history of our species.

I’ve added a bit more from the book. Some of the stuff below I talked about in the last post as well (do recall that I wrote that post before I read this chapter), but I figured it wouldn’t hurt to include it here anyway:

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“The timing of initiation of agriculture varies quite widely […] The exact sequence of events also varies quite widely. For example, in the Near East, sedentism preceded agriculture, at least in the Levantine Natufian sequence, but in Mesoamerica crops seem to have been added to a hunting-and-gathering system that was dispersed and long remained rather mobile […] For example, squash seems to have been cultivated around 10,000 B.P. in Mesoamerica, some 4,000 years before corn and bean domestication began to lead to the origin of a fully agricultural subsistence system […] Some mainly hunting-and-gathering societies seem to have incorporated small amounts of domesticated plant foods into their subsistence system without this leading to full-scale agriculture for a very long time. […] the path forward through the whole intensification sequence varied considerably from case to case.”

“In all known cases, the independent centers of domestication show a late sequence of intensification beginning with a shift from a hunter-gatherer subsistence system based upon low-cost resources using minimal technological aids to a system based upon the procurement and processing of high-cost resources, including small game and especially plant seeds or other labor-intensive plant resources, using an increasing range of chipped and ground stone tools […] The reasons for this shift are the subject of much work among archaeologists […] The shifts at least accelerate and become widespread only in the latest Pleistocene or Holocene. However, a distinct tendency toward intensification is often suggested for the Upper Paleolithic more generally. […] Upper Paleolithic peoples often made considerable use of small mammals and birds in contrast to earlier populations. These species have much lower body fat than large animals, and excessive consumption causes ammonia buildup in the body due to limitations on the rate of urea synthesis […] Consequently, any significant reliance on low-fat small animals implies corresponding compensation with plant calories, and at least a few Upper Paleolithic sites, such as the Ohalo II settlement on the Sea of Galilee […], show considerable use of plant materials in Pleistocene diets. Large-seeded annual species like wild barley were no doubt attractive resources in the Pleistocene when present in abundance and would have been used opportunistically during the last glacial age. If our hypothesis is correct, in the last glacial age no one attractive species like wild barley would have been consistently abundant (or perhaps productive enough) for a long enough span of time in the same location to have been successfully targeted by an evolving strategy of intensification, even if their less intensive exploitation was common. The broad spectrum of species, including small game and plants, reflected in these cases is not per se evidence of intensification (specialized use of more costly but more productive resources using more labor and dedicated technology), as is sometimes argued […] In most hunter-gatherer systems, marginal diet cost and diet richness (number of species used) are essentially independent […], and prey size is far less important in determining prey cost than either mode or context of capture […] For all these reasons, quantitative features of subsistence technology are a better index of Pleistocene resource intensification than species used. We believe that the dramatic increase in the quantity and range of small chipped stone and groundstone tools only after 15,000 B.P. signals the beginning of the pattern of intensification that led to agriculture.”

“Early intensification of plant resource use would have tended to generate the same competitive ratchet as the later forms of intensification. Hunter-gatherers who subsidize hunting with plant-derived calories can maintain higher population densities and thus will tend to deplete big game to levels that cannot sustain hunting specialists […] Once the climate ameliorated, the rate of intensification accelerated immediately in the case of the Near East. In other regions changes right at the Pleistocene-Holocene transition were modest to invisible […] The full working out of agrarian subsistence systems took thousands of years. […] Fully agricultural subsistence systems in the sense of a dominance of domesticated species in the diet typically postdate the origin of agriculture [which they define as “dependence upon domesticated crops and animals for subsistence” – US] by a millennium or more. […] Zvelebil (1996) emphasizes the complexity and durability of frontiers between farmers and hunter-gatherers and the likelihood that in many places the diffusion of both genes and ideas about cultivation was a prolonged process of exchange across a comparatively stable ethnic and economic frontier.”