Human Ancestors Were Nearly All Vegetarians | Guest Blog, Scientific American Blog Network

Paleolithic diets have become all the rage, but are they getting our ancestral diet all wrong?
Human Ancestors Were Nearly All Vegetarians | Guest Blog, Scientific American Blog Network

Extracts :

• In other words, there is very little evidence that our guts are terribly special and the job of a generalist primate gut is primarily to eat pieces of plants. We have special immune systems, special brains, even special hands, but our guts are ordinary and for tens of millions of years those ordinary guts have tended to be filled with fruit, leaves, and the occasional delicacy of a raw hummingbird4.
• Which paleo diet should we eat? The one from twelve thousand years ago? A hundred thousand years ago? Forty million years ago? IF we want to return to our ancestral diets, the ones we ate when most of the features of our guts were evolving, we might reasonably eat what our ancestors spent the most time eating during the largest periods of the evolution of our guts. If that is the case, we need to be eating fruits, nuts, and vegetables?especially fungus-covered tropical leaves.
• But if you want my bet, the majority of the recent (last few million years) changes in our guts and digestion will prove to have had more to do with agriculture than with meat-eating. As hominids and/or humans switched to eating more meat, their bodies might have evolved so to be able to better digest meat. I could be convinced. But, 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. With agriculture, several human populations independently evolved gene variants that coded for the persistence of lactase (which breaks down lactose) so as to be able to deal with milk, not just as babies but also as adults. With agriculture, the species in our guts seem to have evolved too. Some populations of humans in Japan have a kind of bacteria in their guts which appears to have stolen genes for breaking down seaweed, 
• But the truth is, for most of the last twenty million years of the evolution of our bodies, through most of the big changes, we were eating fruit, nuts, leaves and the occasional bit of insect, frog, bird or mouse. And so while some of us might do well with milk, some might do better than others with starch and some might do better or worse with alcohol, we all have the basic machinery to get fruity or nutty without trouble.
• There are, however, trillions of microscopic caveats, trillions of tiny ways I could be wrong. What might be different, either between you and me or between you and me and our ancestors is the sort of gut bacteria we have to help us digest our food. The new era in study of gut bacteria (and their role in digestion)?the era of the microbiome?may reveal that our stone age ancestors, by eating a little more meat, cultivated bacteria that help break down meat, which they then passed on to us (during birth which is messy and has long been), their maybe meat-eating descendents.
• Recent research has revealed that the gut microbes of chimpanzees and gorillas do seem to work a little differently than those of monkeys