Not how we die, but either why it is more advantageous to die or why it's impossible to circumvent death despite the inclination to survive
Originally Answered: Evolutionary Biology: Why do humans die?
From a scientist's perspective, humans die because their only purpose in life is to pass on their genes. But this is a question that can be interpreted in many ways. From an engineer's perspective, humans die because their bodies are complex systems on which the accumulation of damage and malfunctions here and there cause what we call "aging", which in turn causes death. Now, if you are asking it in the same fashion as we ask "Why do humans live?" or "What's the meaning of life?" then, my opinion is that because humans live to learn, then, they die because at some point every lesson finishes :)