What’s funny is that it used to be that those who had a high regard for the well being of their children would breastfeed. That high regard for their children resulted in higher IQ’s, simply from the parent paying attention to and spending time with, and inherently teaching their children.
Then, the left came along and said - “look, breastfeeding makes kids smarter! Let’s push everyone to do it!”.
Well, their program worked, and those who had a low “givadam” factor joined those with a high “givadam” factor, breastfeeding their children, but still neglecting them otherwise, and it exposed the lack of causative relationship of breastfeeding to IQ.
Or it may be that breast milk has a higher fat content then formula. Fat being important in brain development.