Why do we strive for survival?

I'm not sure where this topic goes, so I'm gonna go ahead and stick it into Free Thoughts.

Why do we, human beings (or any other living thing on Earth, really) try to survive for as long as we possibly can? Is it something in our genes, something in our brains or just totally unknown? I mean, it doesn't exactly matter when you die for death arises upon everyone anyway. So why, why do we try NOT to die? Is it the fear of death?

I just want to know, what is it that makes you people, die to survive.
(See what I did there? ;P)

Because all life is built upon this foundation.
Consider this: if some form of life would not strive to survive,  it would be dead thus nonexistent.