The article makes reference to this phenomenon being global: > Yuval Harari says that the worst choice in the history of human societies is when humans made th

The article makes reference to this phenomenon being global: > Yuval Harari says that the worst choice in the history of human societies is when humans made the transition from nomadic hunter-gatherers to sedentary farmers. With this, humans became much more susceptible to malnutrition, disease, and famine. Their grain-heavy diets lacked critical nutrients that are essential to proper brain function. But, we see brain shrinkage in the aboriginal people of Australia and South Africans, who never succumbed to agriculture until recent times, and we see the same amount of shrinkage in these populations as well. It's possible as you say that founder effects and reverse migration and interbreeding could account for this, but an alternative theory is that trade emerged as a driving force of human activity, incentivising new behaviours, and so ultimately it was memetics that changed the selection parameters that shrunk brain sizes