Meat — despite popular movements to decrease the amount humans consume — is still a central part of diets around the world. People who live in industrial countries (like the United States) eat roughly 210 pounds of it each year. And consumption in the developing world, where people eat closer to 66 pounds each year, is climbing fast. Growth is such that by 2030 the average human is expected to consume just under 100 pounds per year, 10 percent more than today. Our collective affinity for meat likely began out of circumstance — humans that lived inland from the coast...