What Is Instinct?

What is it about Human Nature that makes our minds naturally revert to the idea of survival?
 For some instinctual reason we have this behavior mode where we naturally prepare of lives for  the fall of civilization. Just for the  simply fact that the possibility of that scenario could happen in our lifetime. For  example , the actions of replacing a razor blade in my box cutter made me think to fill up the secret compartment within the box cutter with extra razor blades so that if one day a horrible earthquake  was to occur and destroy  everything  in sight, I would be able to use my Box cutter knife to chisel  kindling  so I could make a fire to stay warm at night. How  detailing interesting that  so much thought could  derive from one simply  unthought action. Is it because at some point in  my  existence have I lived threw a devastating earthquake  only to realize I had wished that I was better repaired for the situation I was in and had no control  of.   Is Instinct really past lives lesson we have learned and then later the lesson we learned become a part of soul.