“I have no clue why breastfeeding would make a baby smarter.”
Thinking about what my wife went through to get them to finally breastfeed - it may have nothing to do with the actual milk. But the devotion and love by the mother, willing to try and do everything for her baby. That obviously doesn’t end at breastfeeding.
I’m sure many women would have just gone with regular milk and not put up with all of the stuff my wife did. I’m pretty sure that cow’s milk has also been proven to not have all the right “ingredients” - which would make sense.
And I’m not a big one on eating hormone/chemical free foods, but I imagine that stuff is present in cow’s milk and may have some adverse effects.
Breastfed babies (from a healthy, well-nourished mother) get a basically ideal mix of nutrients for their development. They also get a healthier gut flora which on its own makes them healthier, more resistant to disease, lessens inflammation, and even improves their hormonal balance - again, with effects lasting potentially decades. Children exposed to certain bacteria in infancy have half the cavity rate when they are 9. Other bacteria produce chemicals that affect mood, testosterone production, growth hormone production, and on and on.
There are a lot of ways breastfeeding could have an effect on intelligence.