The worlds oldest profession is being a Chef.
I'd say religion. Before there were ever laws or military or even civilization, there were the religious leaders, shamans, medicine men, healers, prophets, etc. Past food and sex and survival, human's oldest need is how to explain the world around them and how does it work. That's where the role of religious leaders rose.
I would say military. As soon as the spear was invented, there were people who specialized in using it. Certainly law came last, after reading and writing. You could make a case for education being very early, as parents taught their children how to survive, and elders taught the tribe.
The oldest job title in the world is "Parent".
My guess is waring factions among the uncivilized that had to change the face of the world..... Military, Religion, Law, Education.
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