Cordain and Audette allow seeds, but not grains, whereas some Paleo dieters
don't eat seeds for reasons similar to some of those that Cordain and
Audette give re: grains. Why are seeds like sunflower and flax seeds Paleo
but not grass seeds (grain)? What is it about cereal grass seeds that made
them less desirable to Stone Age peoples? 

Here are some reasons that have been given for why grains might not have
been consumed much by Stone Agers (and my questions):
> limited range (Did other kinds of seeds have had wider distribution across
Africa and Eurasia than cereals?)
> short harvesting season--wild grass seeds fall to the ground as soon as
they are ripe (Do other kinds of seeds stay on the plant longer? Flax seeds
were spread through the feces of nomadic Stone Agers who followed the herds
of large game, so why couldn't this have happened just as quickly with grain
seeds?) 

There must have been other factors than these to explain why Stone Agers
didn't eat cereal grass seeds much.

Wrangham of Harvard believes fire-roasted barley seeds at an ancient site in
the Levant 690,000 years old indicates grain eating. Even today Tibetans
roast barley in the sands of a fire. Stone Agers could also have soaked wild
grain before roasting, to reduce the toxins and increase vitamin
availability. Wrangham's evidence is questionable and his conclusion
speculative, but if it turns out to be correct, it would push back the
earliest grain consumption by 663,000 years. Then the reason for lack of
adaptation to eating grain would have to be that people ate only small
quantities or the geographic distribution of the plants was very limited,
rather than that there hasn't been enough time for humanity to adapt.

A vegetarian made this claim in an earlier post: "In some regions wild grass
seed stands are reported to have been so rich, that one person could with
little effort collecte the necessary food for a very long time (that was
*wild* grains, Hans). That was in regions with strong seasons , where plants
have the biggest advantage to produce big annual seeds (and die then),in the
[near] east."

Other related post excerpts:

"*Wild* grains were in fact beginning to be gathered by 17,000 B.C. by
people in the Levant (Middle East) and being ground into flour with
mortar-and-pestle at this time, though cultivation did not begin until
considerably later as Andy states. The Natufians were the successors to the
very earliest grain-gatherers, and were themselves also gathering wild
grains intensively (also using grindstones) around 13,000 B.C. prior to the
introduction of agricultural cultivation." (from Ward N. at
http://maelstrom.stjohns.edu/CGI/wa.exe?A2=ind9705&L=paleodiet&P=R2214 )

"Seed gathering activity was a major activity for the Bagundji [Aborigines]
in the Darling River Basin, although in the Murray River area, tubers were
the main dietary staple.   Early in the last century Mitchell (one of the
first European explorers of Australia) observed as  he travelled down the
Darling River that grass had been gathered and piled in heaps.  Sometimes
the heaped grass (native millet or Panicum sp.) was burnt and the seed
collected [from] the ground."
(http://maelstrom.stjohns.edu/CGI/wa.exe?A2=ind9706&L=paleodiet&P=R608 )