Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 38 to 42.

Very few people in the modern world obtain their food supply by hunting and gathering in the natural environment surrounding their homes. This method of harvesting from nature’s provision is the oldest subsistence strategy, and has been practiced for at least the last two million years. It was, indeed, the only way to obtain food until rudimentary farming and the domestication of wild animals were introduced about 10,000 years ago.

Because hunter-gatherers have fared poorly in comparison with their agricultural cousins, their numbers have dwindled, and they have been forced to live in marginal environments, such as deserts and arctic wastelands. In higher latitudes, the shorter growing season has restricted the availability of plant life. Such conditions have caused a greater independence on hunting, and along the coasts and waterways, on fishing. The abundance of vegetation in the lower latitudes of the tropics, on the other hand, has provided a greater opportunity for gathering a variety of plants. In short, the environmental differences have restricted the diet and have limited possibilities for the development of subsistence societies. Contemporary hunter-gatherers may help us understand our prehistoric ancestors. We know from observation of modern hunter-gatherers in both Africa and Alaska that society based on hunting and gathering must be very mobile. While the entire community camps in a central location, a smaller party harvests the food within a reasonable distance from the camp. When the food in the area is exhausted, the community moves on to exploit another site. We also notice seasonal migration on patterns evolving for most hunter-gatherers, along with a strict division of labor between sexes. These patterns of behavior may be similar to those practiced by mankind during the Paleolithic Period.

With which of the following topics is the passage primarily concerned?