What separates humans from animals? The more we research animal intelligence and behavior, the more we see that we are not so different. At one time, communication was thought to be the main differentiator, but research into chimpanzees, dolphins, and even prairie dogs has found that these animals are also capable of complex communication.
Throughout history, there have been stories of animals committing suicide. Two thousand years ago, Aristotle wrote about a horse that was so ashamed after unknowingly mating with his own mother, that he killed himself. While these types of stories sound improbable, there are cases where animals kill themselves, and no one knows why.