The story behind the brain-destroying mad cow disease vividly illustrates why it’s not a good idea to eat your own species. For cattle, cannibalism had nothing to do with survival or grisly rituals and everything to do with economics.
The first so-called mad cows (the sickness is formally called bovine spongiform encephalopathy) were identified in 1984 in the U.K. They were probably infected a few years earlier by eating feed derived from the parts of sheep, cows and pigs that people avoided—diaphragms, udders, hooves, spinal cords, brains, and the like. The process of separating the ground-up components of slaughtered animals to make feed—and other products such as soap and wax—is called rendering and has existed for hundreds of years. In the mid-20th century in the U.K., rendering demanded the use of solvents and hours of boiling. The procedures presumably destroyed any pathogens that might have come from diseased creatures—pathogens that include the prion, a dangerous, malformed version of a protein found in all mammals.