I was formally diagnosed with ADHD and it continued into adulthood. The only way to suppress it is a diet of raw veggies fruits and meats, combined with like 3 hours of exercise a day and time in nature with silence which my evolutionary ancestors presumably did to survive. The way to make it worse is the combination of sugars, processed foods and flashing stimulus.

Point is I think MOST mental illness is the modern world. If you dumped people with severe depression into their ancestors supposedly worse lives 6,0000 years ago, hunting with tribe and sleeping under starry sky, they’d be fine.