As human societies in the pre-Neolithic period shifted from nomadic to sedentary lifestyles, their organization became more complex and hierarchical. A. The shift to sedentism did not occur in rich habitats, where groups were able to maintain nomadic, foraging lifestyles because of easy access to food sources. B. Changes in diet and activity associated with a sedentary life may have resulted in higher fertility levels and better chances of survival. C. In general, the higher the proportion of protein to carbohydrate in a female individual's diet, the higher the level of that individuals fertility. D. As human populations increased during the Holocene period, they began to exceed the number of people that could be sustained by the local environment. E. The carrying capacities of certain types of regions such as river valleys were limited by the presence of neighbors competing for the same resources. F. Societies responded to the limitations of their environment by developing more complex social and technological strategies that enabled them to produce more food within the same area.