It's an interesting question. There are tons of folks here infinitely more knowledgeable than I on how early man lived. But I like questions that make me think, so here goes.
Before the Nine to Five structure took over our lives, the stress of providing nutrition to ourselves and our children was probably stressful in some climates while being easy as pie in others. But either way, the stress was basically, "Find or kill enough to eat." Though food is plentiful and available now, what we have to do to get it is far from stress-free. We have to be educated enough to find the kind of work that will put food on our tables. Once we get that education, we have to put on a public facade that is acceptable to the PTB that have the jobs to give us. And once we have the job, we have to keep strict hours and compete with others to hold it. And being one's own boss can be even more stressful.
Even getting to that job isn't a matter of taking the wife and kids out to forage, but is squishing in to public transit, or sharing the road with other stressed and tired drivers.
We've also become hypercompetitive in almost everything we do. It's not enough to be a good provider; the 6-figure money mover garners more respect than the 5-figure college professor. It's not enough to be healthy; you have to look like a body builder or fashion model. It's not enough to get good grades; you also have to play soccer, cheer, etc. It's not enough to be pious; you have to show up at church every Sunday so the neighbors know you are. It's not enough to be clean and neat; you have to wear the "uniform" of your peers. Driving a certain kind of car gives you status.
Ever changing technology can be stressful. Being bombarded by news and quasi news.
All of these things are things that stress us if we let them. And that is chronic stress. It's much more than, "Crap, it's getting cold out, now I'm going to have to eat field mouse stew for two months." It's more internal, and it won't kill you from starvation, but it could be shredding you slowly both physically and emotionally.
(All the "you"s above are generic "you"s and not aimed at the op.)