Correlation is not causation. There are many ways that these two traits could become correlated. For example, poverty is associated with both poor childhood nu

Correlation is not causation. There are many ways that these two traits could become correlated. For example, poverty is associated with both poor childhood nutrition (which is possibly the biggest cause of low IQ) and with more outdoor activities (due to more unskilled physical labor, more rural living, fewer electronics at home to keep kids entertained indoors, etc.).