What evolutionary explanations are there for death?
Death is not only for humans. All 'complicated enough' organisms die (with a notable exception of Hydra, though you may argue when it comes to the complexity). It is is easier to create a new organism from scratch than to repair both internal factors (free radicals, metabolic by-products, ...) and external (physical damage, exposure to toxins, ...).
Underlying causes of death actually can be evolutionary beneficial. For example, shortening of telomeres offers protection against cancer (on a cellular level), but also bounds lifespan.
So actually they may be evolutionary competition (within the same species) of young and old. Mutations helping young but harming older may be preferred to the opposite ones.