Sluyter (1993) makes some useful points, but his criticism of Drennan's arguments is unsound. Sluyter is incorrect in thinking that there is no limit to the distance from which human bearers could carry food staples at a net energy profit. Drennan did not take into account that feeding bearers meals supplied at way stations is more efficient than requiring them to carry all their food with them, and he is unrealistic in thinking that a center will rarely procure food from a distance too great to allow more than half of what is procured to reach the center. At least during shortages, food may be procured at a much smaller net energy profit. Nevertheless, Drennan is correct in arguing that there is a limit beyond which (other things being equal) no further increase in procurement radius can increase the food potentially available to the center.