system
Given the following post, respond as if you're commenting on Reddit:
human
[LOTR] How are the Orcs created?

The only thing I took away from the first movie is that they're found underground in some sacs?
gpt
First, every single answer in this thread so far is wrong. 

Orcs do NOT originate from Elves.

Professor Tolkien did extensive research into this topic during his study and the manuscripts he found.  At first he believed the fallen Vala Morgoth created them from stone but later found Morgoth could not create life.  Then he hypothesized Morgoth took Elves and mutated thenlm into Orcs but he quickly REJECTED this idea. There was no way Morgoth could wholly corrupt a race like that,  especially so much so to remove immortality from them as a hereditary trait (orcs are mortal). Tolkien went through several other ideas. Orcs from beasts, Maiar, Men, corssbreeding... he never found an answer.   To this day no one knows the exact origin of the Orc race. Tolkien's latest writings suggest Men may have been the ultimate source, but that would mean his previous research into when Men awoke would need to be greatly reexamined.

Also, orcs reproduce like any other race, they have sex.  The mud sack thing is only in the films.