I’ll throw this in the ring as a possible explanation for why schizophrenia didn’t exist 200 years ago:
High explosive put fear in a new frame. But the essence of it lay in this, that it happened to passive men. Since the discovery of firearms, science has been pushing armies apart, and as long ago as the war with Napoleon, a surgeon with Wellington’s army in Spain found hardly any bayonet wounds. Hand to hand fighting is vanishing out of war, and even veterans have never met cold steel, which was the way death came to the ancients. Once when I had a bayonet a few inches from my belly I was more frightened than by any shell, but it left nothing behind it. It went out of my mind, it would never happen again. Fear takes new shapes, but it used to come upon men suddenly and was gone. The real difference between the war of 1914 and the wars of history lay in the absence of a close period, when men safe for the moment could rest and build up a reserve. It ended inevitably in the breaking of men who would have passed the test of any single day’s fighting with credit; many too were broken for good, they could not come again. There was no rest, no moment’s peace.-Lord Moran, The Anatomy of Courage (emphasis added)
The idea I’m getting at is that schizophrenia may be analogous to repetitive motion injury for the exercise of self-control.
The airman’s need for rest explains the nature of courage. It is the long drawn out exercise of control, which is three parts of courage, that causes wear and tear. This is our homely way of speaking of nervous fatigue, and this fatigue can be measured. One day the barometer of courage will be graduated and we shall be able to watch the glass rise and fall. The worker at his bench needs rest too for he is suffering from the same malady. How many hours in the day and how many days in the week can he work without staleness lowering production? And how much is the work of men of consequence in every walk of life slowed up by this blind industry? The crowds that are now clamouring for the seaside after four years of grinding toil are an expression of a want which can be met only by cancelling some hundreds of trains carrying essential supplies.
Sadly, Moran’s prediction assumed that a society would want to measure courage. (More like Lord Moron.) I think if a researcher pulled that off he’d be burned at the stake by a bipartisan coalition with unanimous support in the broader population.
In an oversocialized environment (ref. Kaczynski) there is no time for rest to replenish this self-control because society is monitoring your every move. This would tend to bother k-selected people more, due to their higher social anxiety, and bother an individual less who’s genetically closer to the norm of his society because following that society’s norms wouldn’t require much self-control. Just think about how much easier it is to study things you enjoy and you’ll have a feel for it. You’d still get fatigued after putting in consecutive 16-hour days, but certainly less fatigued.