The Headland Hypothesis argues that foraging or non-agricultural tribeshave been unable to collect adequate carbohydrates in the rain forest due to itslack of starch producing species, and were thus forced to develop tradeLine relationships with agriculturalists. This hypothesis has been shown to rest on(5) impossibly idealized conceptions of virgin rain forest, forager behavior andhistory, such that one may argue something diametrically different: millennia oftrade relationships with agricultural peoples have led to changes in foragerbehaviors and in the composition of the forests they inhabit. Supposing thathumans modify their environments in ways that are generally favorable toward(10) their continued survival, it follows that an increased reliance on agriculturalistsfor carbohydrates might lead to the gradual disappearance of rain foreststarches. Horticulturalists are likely to dedicate the majority of their effortstoward staple starch crops such as rice or wheat, which in some environmentsmay provide a more efficient source of carbohydrates than does foraging.(15) Foragers, then, would be inclined to assume the "professional primitive" role,and trade more tasty and nutritious rain forest resources such as meat and fruitin exchange for carbohydrates, as Headland himself observed in a multitude ofcultures around the world.Foragers may have also lost some of their knowledge and technologies(20) related to carbohydrate extraction from the rain forest, and the carbohydrate-rich rain forest species may have arrested their co-evolution with foragers,leaving the impression that rain forests have always possessed insufficientquantities of such resources to support humans. A co-evolutionary argument isnot, however, necessary to this line of reasoning, for rain forests may adapt(25) purely in terms of the quantity and availability of extant carbohydrate-richspecies, as the case of sago palms evinces in two ways. Firstly, the selectiveharvesting of some trees has been shown to have a "thinning" effect which helpsthe species to gain sunlight and to thrive, positively affecting its long-termsurvival, reproduction and distribution at the expense of carbohydrate-rich(30) species. Secondly, the sago palm has two means of reproduction: vegetatively,or through "suckers", and through seed disbursal, which whether intentionaland inadvertent is likely to increase when humans are harvesting the trees.Although sago palms are particularlv nrevalent in the areas where, for instancethe Penan foragers exploit it, there has been no study to show that this would(35) remain the case if the Penan were to move, or to cease exploiting the trees.Admittedly, this response to the Headland Hypothesis has problems, fornot all carbohydrate producing species are disbursed by seeds, nor have they allbeen shown to benefit from human foraging behaviors. Theories of co-evolutiondo, however, predict that such relationships would be likely to evolve, and the(40) simple fact that disturbing the rain forest through fire, sago harvesting, andcountless other means available to foragers can lead to better environments forcarbohydrate growth, illustrates that significant changes could have occurred inmuch less time than one might expect. The passage is primarily concerned with discussing（）

A. how anthropologists ought to explain the origins of the trade relationship between foragers and agriculturalists
B. why it is difficult to measure the amount of time necessary for the disappearance of carbohydrate-rich plant species in the rain forest
C. why a particular account of the unavailability of carbohydrates to rain forest foragers is inaccurate
D. what ought to be included in any account of the effects of forager peoples on rain forest ecology
E. what data are most relevant for an accurate account of the relations between rain forest foragers and agriculturalists