>>> Has any source ever seriously examined the question of why humans
>>>would have gravitated toward cereal grains as a primary crop for
>>>agriculture?  Do these plants yield a superior caloric density or
>>>protein content to other vegetation, such as tubers?

Sorry if this is redundant, but we had some posts about this topic a week
or two ago, and someone offered this article:

http://www.vegan-straight-edge.org.uk/GW_paper.htm

-- with some very interesting insights.