The world quietly reached a milestone in the evolution of the human diet in 2011. For the first time in modern history, world farmed fish production topped beef production. The gap widened in 2012, with output from fish farming—also called aquaculture—reaching a record 66 million tons, compared with production of beef at 63 million tons. And 2013 may well be the first year that people eat more fish raised on farms than caught in the wild. More than just a crossing of lines, these trends illustrate the latest stage in a historic shift in food production—a shift that at its core is a story of natural limits.