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For most of human history, we have foraged (hunted, fished, and collected wild plants)for food. Small nomadic groups could easily supply the necessities for their families. No one needed more, and providing for more than one's needs made little sense. The organization of such societies could be rather simple, revolving around age and gender categories. Such societies likely were largely egalitarian; beyond distinctions based on age and gender, virtually all people had equivalent rights, status, and access to resources.
Archaeologist Donald Henry suggests that the combination of a rich habitat and sedentism (permanent, year-round settlement) led to a dramatic increase in human population. In his view, nomadic, simple foragers have relatively low levels of fertility. Their high-protein, low-carbohydrate diets result in low body-fat levels, which are commonly associated with low fertility in women. High levels of physical activity and long periods of nursing, which are common among modern simple foragers, probably also contributed to low levels of female fertility if they were likewise common among ancient foragers.
In Henry's view, the adoption of a more settled existence in areas with abundant food resources would have contributed to higher fertility levels among the sedentary foragers. A diet higher in wild cereals produces proportionally more body fat, leading to higher fertility among women. Cereals, which are easy to digest, would have supplemented and then replaced mother's milk as the primary food for older infants. Since women are less fertile when they are breast-feeding, substituting cereals for mother's milk would have resulted in closer spacing of births and the potential for a greater number of live births for each woman. A more sedentary existence may also have lowered infant mortality and perhaps increased longevity among the aged. These more vulnerable members of society could safely stay in a fixed village rather than be forced regularly to move great distances as part of a nomadic existence, with its greater risk of accidents and trauma.
All of these factors may have resulted in a trend of increasing size among some local human populations in the Holocene (since 9600 B.C.E.). Given sufficient time, even in very rich habitats, human population size can reach carrying capacity, the maximum population an area can sustain within the context of a given subsistence system. And human population growth is like a runaway train: once it picks up speed, it is difficult to control. So even after reaching an area's carrying capacity, Holocene human populations probably continued to grow in food-rich regions, overshooting the ability of the territory to feed the population, again within the context of the same subsistence strategy. In some areas, small changes in climate or minor changes in plant characteristics may have further destabilized local economies.
One possible response to surpassing the carrying capacity of a region is for a group to exploit adjoining land. However, good land may itself be limited-for example, to within the confines of a river valley.Where neighbors are in the same position, having filled up the whole of the desirable habitat available in their home territories, expansion is also problematic. Impinging on the neighbors' territory can lead to conflict, especially when they too are up against the capacity of the land to provide enough food.
Another option is to stay in the same area but to shift and intensify the food quest there. The impulse to produce more food to feed a growing population was satisfied in some areas by the development of more-complex subsistence strategies involving intensive labor and requiring more cooperation and greater coordination among the increasing numbers of people. This development resulted in a change in the social and economic equations that defined those societies. Hierarchies that did not exist in earlier foraging groups but that were helpful in structuring cooperative labor and in organizing more-complex technologies probably became established, even before domestication and agriculture, as pre-Neolithic societies (before the tenth millennium B.C.E.) reacted to the population increase.
B选项说定居民族与游牧民族相比更少地依赖蛋白质了，是对的，因为他们吃谷物多了；来源于：第二段第三句说游牧民族蛋白质高“Their high-protein, low-carbohydrate diets ”，以及第三段第二句说定居民族吃的谷物多“A diet higher in wild cereals”。
A选项说定居民族吃的野生谷物没有游牧民族多，与第三段第二句”A diet higher in wild cereals produces proportionally more body fat”相悖，错误。
C选项说定居民族比游牧民族体力劳动更多，与原文第二段游牧民族“High levels of physical activity”相悖；错误。
D选项说女人更愿意去母乳喂养孩子，原文第三段第三局说是用谷类食物代替母乳喂养“ Cereals… replaced mother's milk as the primary food for older infants”，与原文相悖，错误。