system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Is fear of Death an instinct or a learned behavior?
gpt
“Try to imagine a life without timekeeping. You probably can’t. You know the month, the year, the day of the week. There is a clock on your wall or the dashboard of your car. You have a schedule, a calendar, a time for dinner or a movie. Yet all around you, timekeeping is ignored. Birds are not late. A dog does not check its watch. Deer do not fret over passing birthdays. Man alone measures time. Man alone chimes the hour. And, because of this, man alone suffers a paralyzing fear that no other creature endures. A fear of time running out.” 

- Mitch Albom, The Time Keeper

While other animals certainly mourn the loss of other group members when they die (e.g. chimpanzees, elephants, bonobos), it is unlikely they understand the more abstract concept of their own mortality and death. Thus fear of death is not an instinct, but learned through a higher cognitive understanding of the workings of life. Fear of things that cause death is instinct, because fear and pain are essential for survival.