Evolution towards digesting Starchy foods better.

[We] know our human digestive systems DID evolve to deal with agriculture. With agriculture, some human populations evolved extra copies of amylase genes, arguably so as to better be able to deal with starchy foods.
Rob Dunn - http://blogs.scientificamerican.com/guest-blog/2012/07/23/human-ancestors-were-nearly-all-vegetarians/