To this day, I can recall watching “Predators of the Mara,” a rerun of “Mutual of Omaha’s Wild Kingdom,” on a quiet Sunday afternoon in the early 1980s. In that episode, a cheetah chases down and kills a young wildebeest. It is a remarkably brutal scene of struggle for the wildebeest to get free from the cat’s jaws locked on its neck. The horror I felt as I watched one animal kill another was tempered only by the calming voice of Marlin Perkins, who explained that the herd was ultimately stronger because predators in the Maasai Mara National Reserve helped to cull the sick and the weak. This was natural selection — survival of the fittest.