The co-evolutionary relationship between cows and grass is one of nature’sunder-appreciated wonders; it also happens to be the key to understanding just about everything about modern meat. For the grasses, which have evolved to with stand the grazing of ruminants, the cow maintains and expands their habitatby preventing trees and shrubs from gaining a foothold and hogging the sunlight; the animal also spreads grass seed, plants it with his hooves, and then fertilises it with his manure. In exchange for these services the grasses offer ruminants a plentiful and exclusive supply of lunch. For cows(like sheep,bison, and other ruminants have evolved the special ability to convert grass which single-stomached creatures(like us can’t digest-into high-quality protein)They can do this because they possess what issurely the most highly evolved digestive organ in nature: the rumen. About thesize of a medicine ball, the organ is essentially a forty-five-gallonfermentation tank in which a resident population of bacteria dines on grass.