What proof has been found that proves there was specialization of jobs?

Different working tools.

Explanation:

Many historians often debated whether ancient civilizations already understand the concept of job specialization. (where the people are divided into groups based on their expertise).

To proof Specializations of job exist in ancient civilizations, many historians pointed out to different varieties of tools that is found from their archeological sites. The tools were specifically designed to help the people with specific tasks that can only exist if there was specialization of jobs in that society.

i believe the answer is: returns on investments, no wages

people who belong in upper class society would most likely get there by obtaining multiple source of income, which a certain percentage of ownership for businesses. since most of them are job creator, they would most likely get their money from profit, not wages.