Well I'm not a mother but I want to give a clear scientific point of view:
As it is right now, we haven't even been able to identify all of what the breast milk contains (and that's not a small thing, we even mapped the human genome) . There is so much complex proteins and unique molecules that we still don't know at witch extend they help and start your baby on the right path. Breast milk contains a lot of unique component that help your child brain growth, don't forget that it is still growing a lot after birth. One other thing sure is that steadily, new research shows how it cannot be replaced by any known artificial substitute. It is clearly the best thing for your baby, unless it's not a possibility. They found out (along with other things) that chronic disorders of the intestine are way more prone in persons lactated with artificial milk when they were baby.
I understand that some baby's are allergic to milk and stuff so please don't throw me rocks, but these information's don't come from the random internet. I'm a lot into science, studied it for years and still doing it, my best friend is a MD and I have an other good who is a pharmacist, all freshly graduated, with new knowledge of the modern practice (and Canadian MD's are well reputed all around the world). We talked about breastfeeding recently because I have a girlfriend who don't want to breastfeed because in her head, milk come from cows not women. I was profoundly disappointed in her views. It's the more natural thing on earth, believe me, human body is so complex, nature's know how to take care of herself, usually: we mess it up.
Pls excuse my english
