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CHAPTER 15 • Humans and Preindustrial Climate  281


           Evidence of cultivation in the Fertile Crescent is  The first advanced civilizations of the early Egyptian
        derived from preserved remains of grains found in   dynasties developed between 6000 and 5000 years ago,
        regions where the grains did not naturally grow and  when the monsoon was still considerably stronger than
        where their presence must have been aided by human  it is today. Then and now, Egyptian life centered on the
        efforts. Evidence of permanent occupation of villages  river Nile, fed by monsoon rains in the Ethiopian high-
        comes from the dental remains of animals from the   lands and flowing northward through hyperarid desert
        settlements. Layering in the teeth of these animals indi-  (Chapter 8). When the Nile ran strong, large floods pro-
        cates the season when they died. Because the animals  vided fertile soils and moisture for farming along the
        were killed in all seasons, the people must have stayed  floodplain.
        in the same place throughout the year. By 10,000       Climate in sub-Saharan North Africa turned much
        years ago, people had begun to domesticate cattle and  drier after 5000 years ago as the summer monsoon
        other livestock in the Near East. Near the same time,  weakened. This drying trend affected the civilizations
        people also began to grow barley and other crops in  that had come into existence and grown in size dur-
        northern China.                                     ing the wetter monsoon climates in the preceding
           Because of the close association in time between the  millennia. The weakening of the summer monsoon
        later stages of the deglaciation and the origin of agricul-  after 5000 years ago greatly reduced the extent of
        ture, several cause-and-effect links have been proposed.  summer flooding of the Nile. This change put greater
        One seemingly plausible link is the possibility that the  stress on populations that had expanded in response
        change from the harsh (colder and drier) glacial climate  to the stable food supply from large crop yields in a
        to the more accommodating (warmer and wetter) cli-  monsoonal climate.
        mate provided conditions more favorable for humans to  The Akkadian empire, centered in what is now Syria,
        begin the grand experiment of growing crops.        was the dominant civilization in Mesopotamia until
           On the other hand, climatic data have been used as  4200 years ago. Evidence from archeological investiga-
        the basis for a totally different hypothesis that centers on
        the Younger Dryas climatic reversal between 13,000 and
        11,700 years ago (Chapter 13). According to this idea,                Yucatán
                                                                                18
        the Younger Dryas episode intensified the already dry              lake δ O (    )
        conditions across the eastern Mediterranean region and             1  2   3   4
        forced people to retreat to dependable water sources.           0
        In these more closely clustered conditions, people who
        harvested and ate wild grains may have accidentally
        scattered some grains near their threshing sites, with the                       Cultures
        discarded grains sprouting in succeeding years as a form
        of primitive farming. Some evidence places the time of        500
        the earliest domestication of crops during the Younger
        Dryas.                                                      Years ago                  Mayan collapse Mayan collapse Mayan collapse  Postclassic
           Neither of these directly opposed hypotheses is easy
        to test. One problem is that agriculture may have begun                            Classic
        earlier than the record indicates because the record is      1000
        still incomplete (see Figure 15–7). Another problem is
        that the beginnings of agriculture in each region on                               Late
                                                                                        Late Preclassic
        Earth were one-of-a-kind events. Many such events, each
        related to a similar change in climate, would be required
        for a cause-and-effect relationship to be really conclusive.  1500                 Early

        15-5 Impacts of Climate on Early Civilizations

        Climate change has been hypothesized as the cause of or
        at least a major factor contributing to the deterioration  FIGURE 15-11 Did drought destroy Mayan civilization? Lake
        or collapse of early civilizations. One hypothesis focuses  sediments indicate periods of prolonged drought during the time
        on the role of an early flood (Box 15–1), but drought is a  that Mayan civilization disappeared. (Adapted from J. H. Curtis,
        more commonly invoked factor. In low-latitude regions  D. A. Hodell, and M. Brenner, “Climatic Variability on the Yucatán
        where water was scarce, civilizations were more suscep-  Peninsula (Mexico) During the Past 3500 Years, and Implications for
        tible to drought than to changes in temperature.    Maya Cultural Evolution,” Quaternary Research 46 [1996]: 37–47).
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