Thousands of years ago doesn’t seem a good reference point. With advances in science, technology, better shelters and more accessible food - we absolutely should have way less stress today.
I would also postulate that the average human was happier 20000 years ago than the average human today. I also think that an average duck is happier than an average human.
> I also think that an average duck is happier than an average human.
Perhaps being able to think doesn't help much when it comes to happiness. Thinking is useful practically but it's as if you have to suppress it in order to experience happiness.
My snarky remark would be that with advances in capitalism, we’ve found ever more ways to generate stress.
The less snarky remark would be that Robert Sapolsky has done plenty of research on stress responses in primates and found that the single largest predictor of high stress responses is inequality, which our modern times do seem to generate in abundance.