The Dobe subgroup of the! Kung San were studied by Richard Lee in the 1960s, and provide an example of these interacting constraints. For the Dobe, water is the overriding factor that dictates the location of camps. The camp serves as the home base for 30-40 people, who move out each morning in groups of 2 or 3 to collect plant foods (especially mongongo nuts) or hunt game. All groups must return before evening if they wish to share the common meal. After moving to a new camp, the food resources of the local area (defined by the Dobe as the area within a 2-hour hike) are exploited first. By fanning out in all directions and moving at about 5 km/hour with pauses for rest and work, an area within a 10-km radius can be worked in the space of a 6-hour day.
Once the low-productivity/low-risk resources within this local area have been depleted (i. e., the plant foods and easily collected small game), it is more efficient for the group to move to a new camp than it is for people to spend more and more time walking. A division of labor becomes evident, with younger, more active people making longer trips to mongongo woodlands and the older people and children staying close to the camp and searching for less desirable foods. Any who are not prepared to walk further for the staple mongongo must eat foods such as bitter melons, roots, acacia gum, and the heart of the ivory palm. Richard Lee showed that for mongongo nut foraging, the round-trip distance was the best measurement of the time and energy ‘‘cost’’ of obtaining this desirable food. Camps are moved quite frequently (five or six times in the year), but never very far. A rainy season camp in the mongongo woodland is seldom more than 16-20 km from the previous one, but this is sufficient to shift the spatial focus of exploitation to a new and almost unexploited area.
A 10-km radius is a relatively small territory for hunting the larger game animals, which can move over long distances. Potentially, Dobe hunters must be more mobile than the gatherers and small-game hunters, and the Dobe hunters do sometimes range up to 30 km from a home base using overnight stops, in pursuit of high-yield but high-risk game. However, to do so involves the carrying of much equipment, including water, and the return journey with an animal carcass can be equally arduous. Even for these hunters it is generally more energy efficient to focus on those game available within a 10-km radius.