COLD AND DRY, YES, BUT ABOVE ALL VOLATILE: THE INHOSPITALITY OF PLEISTOCENE CLIMATES TO TRANSITIONS TO AGRICULTURE
VASEY, DANIEL E. Divine Word College.
Pleistocene climatic instability played as large a role in preventing transitions to agriculture as did the widespread cold and aridity. This proposal is based in part on the demography of historic Arctic foragers and other peoples living under highly unstable exogenous conditions. Such
conditions favor systems of small, mobile local populations that gain adaptability to short-term resource variation but tend to maintain wide distances between them and to incur high risks of extinction. Such systems were ill suited to transitions to agriculture.
A high-resolution temperature proxy, oxygen isotope ratios in the GISP2 (Greenland) ice cores, shows swings during Pleistocene stadials that are about 2 1/2 times as large as those during the Holocene. Figure 1 charts 20-year averages from 16490-4000 BP (after Meese et al 994; Stuiver et al 1997; Stuiver, Grootes, and Braziunas 1995; Steig, Grootes, and Stuiver 1994). Figures 2 and 3 show observations during periods in the Younger Dryas and early Holocene, respectively (after Grootes, Stuiver 1997; Grootes et al 1993; Meese et al 1994; Stuiver, Grootes, and Braziunas 1995; Steig, Grootes, and Stuiver 1994). Temperatures decrease towards the bottom of each graph. The data were obtained from the World Data Center for Paleoclimatology.
Agriculture arose independently, involving separate sets of domesticated plants and animals, in at least eight places, probably eleven, and possibly more. All domesticates whose identification is generally accepted and unambiguous date from the Holocene, though in one place, the Levant, domestication and intensified management of plants probably began during the Younger Dryas.
The absence or near absence of agriculture during the Pleistocene begs explanation. A partial one lies in the widespread cold and aridity. Holocene climates in which agriculture emerged ranged from tropical to middle temperate and from semiarid to humid. Excluding other climates, as well as the Americas, whose occupation is uncertain before ca. 15,000 BP, the area of favorable biomes during stadials was about a third of its extent at the Holocene Optimum, when the Americas are included. Nonetheless, all the plants and animals that were later domesticated survived somewhere in the Pleistocene. Anatomically modern humans occupied the habitable parts of Africa, Asia, Europe, and Australia-New Guinea before 35,000 BP, warm parts well before that. Opportunities for human exploitation of the plants and animals that were later
domesticated thus extended over a very long period before the Holocene, compensating the reduced favorable area. More is needed in the way of explanation.
This paper reverses the logic of previous climatic explanations of transitions to agriculture. In them changes in temperature or precipitation stressed populations of foragers, forcing change, or created conditions favorable for unintentional domestication. Holocene climates have been particularly stable. If climatic change alone led to agriculture, it should have happened many
times during the Pleistocene. Holocene domesticates had survived Pleistocene climatic shocks, but the food available to humans, whether from these same plants and animals or others, possibly varied greatly under Pleistocene conditions. This paper relates resource variation to the proposed population system.
Grootes, P.M., and M. Stuiver. 1997. Oxygen 18/16 variability in Greenland snow and ice with 10^3 to 10^5-year time resolution. Journal of Geophysical Research 102:26455-26470.
Grootes, P.M., M. Stuiver, J.W.C. White, S.J. Johnsen, and J. Jouzel.1993. Comparison of oxygen isotope records from the GISP2 and GRIP Greenland ice cores. Nature 366:552-554.
Meese, D.A., R.B. Alley, R.J. Fiacco, M.S. Germani, A.J. Gow, P.M. Grootes, M. Illing, P.A. Mayewski, M.C. Morrison, M. Ram, K.C. Taylor, Q.Yang, and G.A. Zielinski. 1994. Preliminary depth-age scale of the GISP2 ice core. Special CRREL Report 94-1, US.
Stuiver, M., T.F. Braziunas, P.M. Grootes, and G.A. Zielinski. 1997. Is there evidence for solar forcing of climate in the GISP2 oxygen isotope record? Quaternary Research 48:259-266.
Stuiver, M., P.M. Grootes, and T.F. Braziunas. 1995. The GISP2 18O climate record of the past 16,500 years and the role of the sun, ocean and volcanoes. Quaternary Research 44:341-354.
Steig, E.J., P.M. Grootes, and M. Stuiver. 1994. Seasonal precipitation timing and ice core records. Science 266:1885-1886.
Figure 1. Bidecadal Oxygen Isotope Ratio Averages, 16490-4000 BP, GISP2 Ice Core.
Figure 2. Oxygen Isotope Ratios, 11600-11900, GISP2 Ice Core.
Figure 3. Oxygen Isotope Ratios, 7300-7600, GISP2 Ice Core.
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