The record of human modification of the environment spans at least 2.5 million years. During this period, changing climates would have resulted in changes and uncertainties in the availability of critical resources (e.g., food and water). Hominins that survived such uncertainty must have adapted to these challenges, with key evolutionary innovations altering the ways in which human ancestors interacted with their surroundings. New technologies variously involving the use of stone, the intensified hunting of animals and reaping of wild plants, and the potential to build shelters, to clear landscapes using fire, and to play a role in extinctions of other organisms, together with the developing ability to communicate and plan coordinated activity—all set the stage for a fundamental change in human ecology involving the transition from mobile hunting-gathering to food production and the emergence of human-dominated ecosystems. Framed in the context of late Pliocene and Pleistocene climate change, the capacity to make tools, exploit new foods, control fire, build durable shelters, and organize complex social activity reflect evolutionary responses that enabled human ancestors to survive and adapt to environmental risks and uncertainties (Potts, 1996b, 1998). The initially simple capacities to alter their immediate surroundings proved so successful that they enabled humans to spread over the planet and thus, ultimately, to induce environmental change on a global scale.

The most profound human modifications of ecosystems resulted from the transition from food foraging (e.g., hunting-and-gathering) to food production (e.g., farming, herding). This fundamental change in how humans acquired food involved a transition from dependence on wild food sources sought and found each day, involving much of the population, to dependence on food that could be grown and stored by a much smaller subset of the population (Flannery, 1986; Zeder, 2006). The investment in fields and food production meant that originally highly mobile groups became sedentary. Populations grew in size due to the existence of a more stable food supply, which also enabled some members of the population to become specialized craftsmen, artists, inventors, religious and political figures, along with the many other roles that people adopt in modern society (Diamond, 1997). The following is a summary of several distinct developments over the long course of human evolution that provided the antecedents to this critical transition.

Technology At present, the oldest documented stone tools attributable to hominins are dated to nearly 2.6 Ma (Semaw et al., 2003). Pliocene toolmaking involved the manufacture of sharp-edged stones (by using other stones as percussors) and the use of rocks for crushing and pounding. Even the simplest cutting and crushing activities enabled early hominin toolmakers to gain access to new higher-quality foods (e.g., animal fat and protein, or buried tubers and roots) (Potts, 1996b). From this simple technological beginning, a large array of food

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