The article has a lot of information about this but just to start formula, while it is fortified with iron and other vital vitamins it doesn't contain half of what breastmilk can provide. This even includes certain antibodies that can be transferred from mother to child. Interestingly, nursing is said to foster a closer relationship between the mother and child...I'm not a mother but I've heard people talk about this and I think that psychological bonding through nursing is just as important as anything else.