Years ago I could hardly contain my repulsion as I watched a group of chimps eating the guts of a screaming monkey. The film was one of a series of British Broadcasting Corporation nature films being shown at an international ethological conference. Only our being ethologists gave us entry into the forbidden world of chimp aggressiveness because the film had been censored to keep public ecological enthusiasm up and running. Who would support conservation efforts after seeing a scene of such cruelty? The BBC crew assured us that adult chimps normally kill their prey before eating it and that these were young chimps training in the art of hunting. Or maybe they were just playing with their food?
Years later, in the Toronto Zoo, I watched an orangutan mother play with her newborn in a way that looked very much like child abuse. I also remember watching from a shore
Brunner D. Demonic Males: Apes and the Origins of Human Violence. JAMA. 1997;278(21):1791-1792. doi:10.1001/jama.1997.03550210089048