Society for American Archaeology Was Agriculture Impossible during the Pleistocene but Mandatory during the Holocene? A Climate Change Hypothesis Author(s): Peter J. Richerson, Robert Boyd, Robert L. Bettinger Source: American Antiquity, Vol. 66, No. 3 (Jul., 2001), pp. 387-411 Published by: Society for American Archaeology Stable URL: http://www.jstor.org/stable/2694241 Accessed: 28/11/2010 19:40 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. 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Bettinger Several independent trajectories of subsistence intensification, often leading to agriculture, began during the Holocene. No plant-rich intensifications are knownfrom the Pleistocene, even from the late Pleistocene when humanpopulations were oth- erwise quite sophisticated. Recent datafrom ice and ocean-core climate proxies show that last glacial climates were extremely hostile to agriculture-dry, low in atmospheric CO2, and extremnel)'variable on quite short time scales. We hypothesize that agriculturewas impossible under last-glacial conditions. The quite abruptfinal amelioration of the climate wasfollowed imme- diately by the beginnings of plant-intensive resource-use strategies in some areas, although the turn to plants was much later elsewhere. Almost all trajectories of subsistence intensification in the Holocene are progressive, and eventually agriculture became the dominant strategy in all but marginal environments.We hypothesize that, in the Holocene, agriculture was, in the long run, compulsory. We use a mathematical analysis to argue that the rate-limitingprocess for intensification trajectories must generally be the rate of innovation of subsistence technology or subsistence-relatedsocial organization.At the observed rates of innovation, population growth will always be rapid enough to sustain a high level of population pressure. Several processes appear to retard rates of cultural evolution below the maxima we observe in the mostfavorable cases. Variastrayectorias independenties de la intensificaci6ndel sustento, muchasde las cuales conducierona la agricultura,empezaron duranteel Holoceno. No conocemos ninguna intensificacio que usara muchos recursos vegetales duranteel Pleistoceno, inclu- sive el Pleistoceno iltimo, cuando las poblaciones humanasfueron muy sofisticadas en otros dmbitos.Datos recientes de cilin- dros de hielo sacados de Groenlandia,y de sedimentosocec'nicos, muestran que la l'ltima glaciaci6nfue' extremadamentehostil a la agricultura,ya quefue-seca, baja en C02, y extremadamentevariable en el corto plazo. Proponemosque la agriculturafue imposible en estas condiciones de la l'ltima glaciaci6n. La sabita mejora del clima alfinal de la glaciaci6nfue' seguida inmedi- atamentepor la iniciaci6n de usos mas intensivosde los recursos vegetales en algunos lugares, aunquemucho mas tarde en otras partes. Casi todo las trajectoresde intensificaci6nen el Holoceno eran occurrieronsin retroceso. Finalmente,la agriculturase convirti6en el modoprincipal de sustento en todas partes, exceptopor zonas muyfrias o muy secas. En el Holoceno, hacemos el hip6tesis que la agriculturase vuelve, a final de cuentas, obligatoria. Usamos un andlisis matemdticopara formular el hip6the- sis que los procesos limitantede la taza de intensificaci6ndebe generalmenteser la taza de la inovaci6ntecnol6gica en las estrate- gias de sustento, o la taza de inovaci6n en lasformas de organazaci6nsocial en relaci6n al sustento. Con las tazas de inovaci6n que se observan, el crecimientode la poblaci6n siempre es suficientementerapido como para crear alto nivel de presion pobla- cional. Al parecer, varios processos normalmenteretardan la velocidad de la evoluci6n cultural abajo de las tazas mdximasque observamosen el modelo. E volutionarythinkers have long been fascinated V. GordonChilde wrote influential books andpapers by the origin of agriculture.Darwin (1874) on the origin of agriculturein the 1920s and 1930s declinedto speculateon agriculturalorigins, (see Flannery1973 andMacNeish 1991:4-19 for the but twentieth-centuryscholars were bolder. The intellectualhistory of the originof agricultureques- Sovietagronomist Nikolai Vavilov, the American geo- tion). These explorationswere necessarilyspecula- grapherCarl 0. Sauer,and the Britisharchaeologist tive andvague, but stimulated interest in thequestion. Peter J. Richerson * Departmentof EnvironmentalScience and Policy, University of California-Davis, Davis, CA 95616, [email protected] Robert Boyd * Departmentof Anthropology,University of California-LosAngeles, Los Angeles,CA 90095, [email protected] Robert L. Bettinger * Departmentof Anthropology,University of California-Davis,Davis, CA 95616, [email protected] AmericanAntiquity, 66(3), 2001, pp. 387-411 Copyright? 2001 by the Society for AmericanArchaeology 387 388 AMERICAN ANTIQUITY [Vol. 66, No. 3, 2001 Immediatelyafter WorldWar II, the American gathererspersisted to recenttimes in areasseemingly archaeologistRobert Braidwood (Braidwood et al. highly suitablefor agriculture,most notablymuch 1983)pioneered the systematicstudy of agricultural of westernNorth America and Australia.Attempts origins.From the knownantiquity of village sites in to accountfor this rathercomplex pattern are a major the Near East and from the presenceof wild ances- focus of archaeology. tor species of many crops and animaldomesticates in the sameregion, Braidwood inferred that this area Origin of Agriculture as a Natural Experiment was likely a locus of early domestication.He then in Cultural Evolution embarkedon an ambitiousprogram of excavationin The processesinvolved in such a complex phenom- the foothillsof the southernZagros Mountains using enon as the origin of agriculture are many and a multidisciplinaryteam of archaeologists,botanists, denselyentangled. Many authors have given climate zoologists, and earthscientists to extractthe maxi- change a key explanatory role (e.g., Reed mum useful informationfrom the excavations.The 1977:882-883). The coevolutionof humansubsis- availabilityof 14C dating gave his team a powerful tence strategiesand plant and animaldomesticates tool for determiningthe ages of the sites. NearEast- must also play an importantrole (e.g., Blumlerand ern sites older thanabout 15,000 B.P. excavatedby Byrne 1991; Rindos 1984). Hunting-and-gathering Braidwood(Braidwood and Howe 1960) andothers subsistencemay normallybe a superiorstrategy to were occupied by hunter-gathererswho put much incipientagriculture (Cohen and Armelagos 1984; moreemphasis on huntingand unspecializedgath- Harris 1977), and, if so, some local factor may be eringthan on collecting and processingthe seeds of necessaryto provide the initial impetus to heavier especiallyproductive plant resources (Goring-Mor- use of relativelylow-quality, high-processing-effort ris and Belfer-Cohen1998; Henry 1989). Ages are plantresources that eventually result in plantdomes- given here as calendardates before present(B.P.), tication.Population pressure is perhapsthe most pop- where presentis taken to be 1950, estimatedfrom ular candidate(Cohen 1977). Quite plausibly,the 14C dates accordingto Stuiveret al.'s (1998) cali- complex details of local historyentirely determine brationcurves. The Braidwoodteam showed that the evolutionarysequence leading to the origin and about 11,000 years ago, hunter-gathererswere col- spreadof agriculturein everyregion. Indeed, impor- lecting wild seeds, probablythe ancestorsof wheat tantadvances in our understandingof the originsof and barley,and were huntingthe wild ancestorsof agriculturehave resultedfrom pursuitof the histor- domestic goats and sheep. At the 9000 B.P. site of ical detailsof particularcases (Bar-Yosef1998; Flan- Jarmo,the team excavatedan earlyfarming village. nery 1986). Using much the same seed-processingtechnology Nonetheless,we proposethat much about the ori- as theirhunter-gather ancestors 2,000 years before, gin of agriculturecan be understoodin termsof two the Jarmopeople were settledin permanentvillages propositions: cultivatingearly-domesticated varieties of wheatand Agriculture WcasImpossible During The Last barley. Glacial. Duringthe last glacial, climates were vari- Numerous subsequentinvestigations now pro- able andvery dry