Thinking in “jobs”

When and why did we start doing it?

One of the things I’m curious about is the very concept of “jobs.” 

Of course, we’ve always had to “work” (meaning, take some sort of action / create some sort of change in our environment) to acquire the food and shelter we need to survive.

But when did we start thinking of it as “work” or as a “job”?  When did we begin compartmentalizing that experience as separate from the rest of living? What societal purpose did that serve?

Let alone: when did (some of us) start to wrap our identity around our “job”?  

I already have some reading material singled out to dive into, and I’m sure there’s a lot more out there that isn’t yet on my radar.  Can’t wait to report back here on this topic periodically, but for now, we’ll just sit with the question:

Why do we think in “jobs” in the first place?