216 climate and geography: Africa the time, this habitat was limited to tropical Africa’s savannawoodland border Climatic conditions that produced a moist, warm period in southern Africa from approximately 900 to 1300 allowed for the development of the Mapungubwe civilization (ca 1075–ca 1270) in present-day Botswana and Zimbabwe This herding and trading civilization boomed during the moist period but disappeared in the mid-13th century, just as the climate began to change Shona pastoral settlements then developed in the highland areas to the north, around the city of Great Zimbabwe, between 1275 and 1450 This Shona civilization collapsed during the latter half of the 15th century, but the impact of the great numbers of humans that had lived in the area left the landscape forever changed, denuded and stripped of many of its native trees Climate and Disease Disease shaped human settlement and migration patterns throughout the African continent during the medieval period The rainfall boundary of 40 inches was then quite important to humans, because it represented the lower limit of the tsetse fly habitat Herders tended to live farther north, where rainfall levels were lower, to prevent infection of their herds by sleeping sickness, which was particularly fatal to large livestock Since the Intertropical Convergence Zone moved farther to the north during part of the Medieval Warm Period, so also did the pastoral inhabitants who made their livelihoods in the grasslands free from the tsetse fly Although rainfall was sufficient to grow certain cereal crops in the area just south of the Sahel, inhabitants of this area could not use large plow animals to cultivate the soil, also due to sleeping sickness, which limited the expansion of farmland Sleeping sickness further necessitated the use of human porters, rather than large domestic animals, for trade in areas where the tsetse fly was common Another African disease that affected human societies was bilharziasis, or schistosomiasis, which was transferred to humans through contact with bodies of water that were home to the disease’s snail hosts Malaria and measles were also common concerns, though low population densities served to limit the capacity of these diseases to become endemic during the medieval period The threat of widespread endemic diseases accompanied the increases in population densities seen from this time period onward, as the rising of the great medieval civilizations led to the growth of urban areas and more frequent use of close living quarters Livelihoods Many of the common livelihoods of the medieval period were closely related to and shaped by the climate and by the geo- graphic nature of the land Farmers were constrained by the need for rainfall sufficient to grow crops; after the decrease in rainfall between 1100 and 1400, farmers largely remained below latitude 18 degrees north Pastoralists, again, were geographically constrained by sleeping sickness Human groups in the central rain forests tended to maintain their huntergatherer livelihoods because the soils could not sustain longterm fertility if cleared for farming As such, population densities were lower in this region Pastoralists from dry areas of the Sahel-Sahara border region tended to engage only in herding, rather than making livings through a variety of occupations, because entire communities needed to possess particular specialized skills to ensure the survival of their herds and themselves In the Great Lakes region of eastern Africa, on the other hand, pastoralists found the raising of cattle and other animals much easier owing to the plentiful rainfall and kinder environmental conditions They were therefore able to devote additional time to the development of agriculture, establishing productive banana and fishing industries The nature of the ocean currents off the shores of Africa, in fact, produced certain areas with rich fishing grounds Cool currents provided particularly plentiful ocean harvests near the shorelines of present-day Morocco, on the western Sahara coast, and Namibia, on the western Kalahari and Namib desert coasts Trade through both the Arabian and trans-Saharan networks developed, and it was sustained because of Africa’s rich supplies of natural resources Thus, social interdependence only grew during this time period, both within communities and between communities In turn, increased opportunities for trade allowed persons to specialize more frequently in one particular skill, such as craft work Greater supplies of goods, in turn, fostered further increases in trade and specialization as well as the development of castes based on professional trades and of hierarchically organized social systems Natural Resources Many African groups had the technology to smelt copper and iron long before the start of the medieval period This technology had reached southern Africa by the turn of the 11th century The process of iron smelting required the harvesting of grand numbers of trees for the production of charcoal As such, the clearing of forests transformed the landscape, exposing the soil to the elements, which led to increased erosion and decreases in soil fertility However, this process also aided human settlement because forest clearing opened up land for farming—at least until the soil nutrients were sapped—and eliminated the habitat of the disease-carrying tsetse fly Furthermore, the invention of iron tools increased agricultural