" The obvious question is, what are the “conditions to which presumably we are genetically adapted”? As it turns out, what Donaldson assumed in 1919 is still the conventional wisdom today: our genes were effectively shaped by the two and a half million years during which our ancestors lived as hunters and gatherers prior to the introduction of agriculture twelve thousand years ago. This is a period of time known as the Paleolithic era or, less technically, as the Stone Age, because it begins with the development of the first stone tools. It constitutes more than 99.5 percent of human history—more than a hundred thousand generations of humanity living as hunter-gatherers, compared with the six hundred succeeding generations of farmers or the ten generations that have lived in the industrial age.
It’s not controversial to say that the agricultural period—the last .5 percent of the history of our species—has had little significant effect on our genetic makeup. What is significant is what we ate during the two and a half million years that preceded agriculture—the Paleolithic era. The question can never be answered definitively, because this era, after all, preceded human record-keeping. The best we can do is what nutritional anthropologists began doing in the mid-1980s—use modern-day hunter-gatherer societies as surrogates for our Stone Age ancestors. "

― Gary Taubes , Why We Get Fat: And What to Do About It