A guest blogger at Discover magazine tackles some recent evidence that our hominin ancestors ate more grain than we might think. Her conclusion:
So while there remains little doubt that many modern humans eat too much sugar and processed foods, these studies show that identifying a particular “paleo” diet is impossible. Researchers are just beginning to understand what ancient humans ate, and these recent studies show that grasses and grains have been part of the human diet for millions of years.
Read the rest. You may find the comments interesting.
Paleo Diabetic 
That article was nonsense.
The original research shows that our distant ancestors shifted their diet from C3 carbon sources (which actually includes wheat, fruit and so on AND the animals and insects that fed on these) to C4 carbon sources (including grasses and corn – a new world food our ancestors never saw and which didn’t exist then anyway) OR the animals that fed on them, and the honey made from their pollen.
http://unews.utah.edu/news_releases/a-grassy-trend-in-human-ancestors-diets/
It can be taken as evidence that these hominids ate butter as well as corn, if you like.
And it EXCLUDES these distant ancestors eating modern grains like wheat and rice, which are C3 foods.
It really just confirms that said ancestors moved from the forest to the savannah, which everybody knew.
And that the guest blogger is an idiot. I am not surprised that her other job is blogging about eating disorders.