Did the "Three meals a day" routine come into play with the advent of the farmers?

Farming began 5000–7000 years ago. Since farming was probably the first organized form of labor, you are probably correct in assuming that this brought a more regular routine to the human race.

Before that, and in hunter-gatherer cultures, I would think they didn’t save food because meat spoils, so I’m guessing they ate soon after they caught something.

I think it developed out of our natural bodies rhythms

Probably so. Good thing I wasn’t around then, I’m of the 5–6 meals a day person. Small meal… small ;-)

@SeventhSense I think our habits dictate the rhythm of our bodies. I think the “natural” rhythm would be to eat a little here and there as it became available, and as we got hungry. I mean, we are animals…and the only animals that eat at “specific” times…I recently started eating breakfast every morning at the same time (7:30 a.m.—new job has me on a schedule) and within a week I found that I was hungry at that same exact time every morning (7:32 a.m.), whereas before I’d eat for the first time in a day around 10 or 11…or 2 or 3.

@Dutchess12
Yes probably. I mean if you’re up for 15–16 hours a day your probably going to want to eat at least every 5 hours whatever your schedule. Primitive man probably ate when the tribe had food or grazed like chimps and then this became more ordered as they were succesful in farming and agriculture.