Could be that there is a kind of developmental switch. If life is tough as a child, it makes sense to speed up development to improve odds of survival. If you find yourself in a safe, loving and caring place, then you have the option of spending more time and energy developing the brain.
> life was hardship and adversity
Not necessarily. Many argue that hunters and gatherers lived a much better life than during most of recorded history. There is plenty of evidence for this. It's entirely possible that a child would find itself in a small, well functioning group of people, without any major adversity during childhood.
> Could be that there is a kind of developmental switch. If life is tough as a child, it makes sense to speed up development to improve odds of survival.
Sounds reasonable. In crowded waters fish start to mature at a much younger age.
Source: studied farming and a non trivial part of the curriculum was related to taking care of fishing and hunting resources.
Agriculture is also more intensive than hunting / gathering, supporting more humans per area. When the two conflicted, the agriculturalists won by strength of numbers.
Generally, more intensive civilizations outcompete less intensive ones, even though the average individual may be worse off in that society.
> life was hardship and adversity
Not necessarily. Many argue that hunters and gatherers lived a much better life than during most of recorded history. There is plenty of evidence for this. It's entirely possible that a child would find itself in a small, well functioning group of people, without any major adversity during childhood.