The Headland Hypothesis argues that foraging or non-agricultural tribes
have been unable to collect adequate carbohydrates in the rain forest due to its
lack of starch producing species, and were thus forced to develop trade
relationships with agriculturalists. This hypothesis has been shown to rest on
(5) impossibly idealized conceptions of virgin rain forest, forager behavior. and
history, such that one may argue something diametrically different: millennia of
trade relationships with agricultural peoples have led to changes in forager
behaviors and in the composition of the forests they inhabit. Supposing that
humans modify their environments in ways that are generally favorable toward
(10) their continued survival, it follows that an increased reliance on agriculturalists
for carbohydrates might lead to the gradual disappearance of rain forest
starches. Horticulturalists are likely to dedicate the majority of their efforts
toward staple starch crops such as rice or wheat, which in some environments
may 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 fruit
in exchange for carbohydrates, as Headland himself observed in a multitude of
cultures 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 insufficient
quantities of such resources to support humans. A co-evolutionary argument is
not, however, necessary to this line of reasoning, for rain forests may adapt
(25) purely in terms of the quantity and availability of extant carbohydrate-rich
species, as the case of sago palms evinces in two ways. Firstly, the selective
harvesting of some trees has been shown to have a "thinning" effect which helps
the species to gain sunlight and to thrive, positively affecting its long-term
survival, 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 intentional
and inadvertent is likely to increase when humans are harvesting the trees.
Although sago palms are particularly prevalent in the areas where, for instance
the 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, for
not all carbohydrate producing species are disbursed by seeds, nor have they all
been shown to benefit from human foraging behaviors. Theories of co-evolution
do, however, predict that such relationships would be likely to evolve, and the
(40) simple fact that disturbing the rain forest through fire, sago harvesting, and
countless other means available to foragers can lead to better environments for
carbohydrate growth, illustrates that significant changes could have occurred in
much 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