A Type D personality is distressed, Type D's have a negative outlook towards life and are pessimistic. A small event that is not even noticed by type B can ruin type D's day. Type D personalities are more subject to depression than other personality types.
For most of human history, horses were seen as prey to be hunted for sustenance. During the late Pleistocene, around 55,000 years ago, Neanderthals scavenged off of horse carcasses and made occasional kills of their own.
Thousands of years ago, before horses were domesticated, their main predator was the wolf. Wolves were one of the few animals that were fast enough and smart enough to chase, catch, kill and eat horses. Even now, the wolf is one of the few predators that eats wild horses. Grizzly bears and mountain lions may also occasionally attack a horse.