Disease and intelligence: Mens sana in corpore sano | The Economist
"Places that harbour a lot of parasites and pathogens not only suffer the debilitating effects of disease on their workforces, but also have their human capital eroded, child by child, from birth."
It's interesting to note that malnutrition will also cause the brain to develop poorly, so feeding the hungry is not the only answer. Niether is tending to the infirm the answer. It requires both to help us lift each other up.
This might also help to explain the why there was such an up lift along the nile. Nubians where dosing themselves with antibiotics using beer as far back as 1,700 years ago. It makes me wonder if other culture that fermented foods received a comparable boost.