Whether or not agriculture was the “worst mistake in the history of the human race,” the choice, once made, was made for good. With a global population of seven billion people, heading rapidly toward eight billion, there’s certainly no turning back now (even if paleo does, in fact, prevent zits). Pound for pound, beef production demands at least ten times as much water as wheat production, and, calorie for calorie, it demands almost twenty times as much energy. Livestock are major sources of greenhouse-gas emissions, not just because of the fuel it takes to raise them but also because they do things like belch out methane and produce lots of shit, which in turn produces lots of nitrous oxide. One analysis, published in the American Journal of Clinical Nutrition, concluded that, in terms of emissions, eating a pound of beef is the equivalent of driving forty-five miles. (Grass-fed beef—recommended by many primal enthusiasts—may produce lower emissions than corn-fed, but the evidence on this is shaky.) Eating a pound of whole wheat, by contrast, is like driving less than a mile. All of which is to say that, from an environmental standpoint, paleo’s “Let them eat steak” approach is a disaster.