Like any other species on this planet, human beings are ardent survivors in a challenging environment. Evolution has bestowed upon us the gift of a more exceptional brain than our primate counterparts, allowing us to break away from most of the trials and tribulations which almost every species on Earth has to contend with: Without our superior technology, Man will most likely be at the mercy of ferocious beasts (and they still do: occasionally, and sometimes quite often, stories of humans being bitten and eaten by animals remind us that without our fancy blink-blinks and weaponry, we are as vulnerable as suckling babies) in the natural environment.
Death is defined as the cessation of life: Quite clearly, death is comparable to a full-stop in a single sentence. A single sentence will still resume after a comma, which represents a single pause, but a full stop spells the inevitable end. Death works the same way: When life ceases to continue, death becomes the inevitable end to life. From the tiniest of microbes to living human beings, death is an inescapable fate of living things.