"...began to fall in 1963, when the Partial Nuclear Test Ban Treaty was enacted, and by 2008 it had decreased to only 0.005 mSv/yr above natural levels. This has made special low-background steel no longer necessary for most radiation-sensitive uses, as new steel now has a low enough radioactive signature."
I mean natural variation as in genes. Trauma often triggers mental health problems, but there usually needs to be genetic susceptibility as a foundation for it to happen.
Could it be that everything we call mental illness is just natural variation of people's psyche, at the ends of the bell curve?
Many of the mental illnesses are of course bad, but in an evolutionary perspective it makes sense that we have these variations in a population, to optimise adaptation.
I remember having the iPhone 2G back in 2007, and that someone created a way to store a 5GB wikipedia dump (the complete wikipedia at that time, but without photos) on it, so you could have the whole Wikipedia in your pocket. At the time it felt pretty amazing.