system
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human
[LOTR] Why do humans have shorter lifespan than other races? Or in other words, why do other races live longer?

Elves I do kinda understand, but it seems that Dwarves and Hobbits also tend to live quite longer than humans as well.
gpt
God's plan.

Elves are immortal. Their souls are bound to the Earth and will live as long as it exists.

This however is not something to be envied.

God gave Men the Gift. They can shape their lives outside of the Music of the Ainur and in the end the Die and depart the circles of the world.  Where they go is unknown but many speculate it is to be with God in the Timeless Halls. While Men sometimes call it the Doom rather than the Gift (Melkor instilled a fear of death in them) it is said that the Elves, and even the Valar, in time will envy Men and their fate.

Dwarves are mortal as well but their fate is unknown. Some believe they have their own place in the Halls of Mandos and wait for the the End.

Hobbits are a branch of Men and recieve the Gift.  They do tend to live a bit longer it seems (they don't come of age until 30) but not extremely so.

Note:  Aragorn lives very long for a Man (210).  However this is due to the gift of longer life granted to the Dunedain not because he has a distant Elvish ancestry as is commonly thought.