(Copy and pasted from somewhere else, but it really does matter. Studies show that the body and brain composition of a formula fed infant is very different to that of a breastfed infant)
"Infant formula inevitably creates gut dysbiosis which in turn programmes different development trajectories than breastmilk would have.
So MRI studies show differences in brain white matter development and electrical activity under 12 months of age, ultrasound studies reveal differences in reproductive tissue development by 4 months of age (less testicular tissue in boys, more ovarian tissue in girls), body tissue composition and deposition is different, there is more DNA damage and chromosomal breaks in infants not breastfed (discovered by cancer researchers wanting an explanation for higher rates of childhood cancers in not breastfed children); kidneys are enlarged and thymus shrunk.. the list is much longer...as is the list of harms to the women who do not breastfeed.
Anyone really wanting to know the science should read Milk matters: infant feeding and immune disorder, which argues that the almost universal exposure to infant formula by the mid 20th century is responsible for ongoing and heritable damage. The evidence (fully referenced) comes from industry-sponsored scientists. Alas, revealing it to parents is the last taboo, with those who know some of it bullied into silence by allegations that they are simply trying to shame women. (Rather than save lives and prevent disease.)
The World Health Organisation, a deeply conservative and controversy-avoiding organisation, urges exclusive breastfeeding to around six months and continued breastfeeding into the second year and beyond for good reasons, like the free stem cell transplants it provides to every baby, rich or poor.
Breastmilk is a living tissue, and lactation an entirely natural process that bodies switch on after birth unless prevented by breast disorders or lactation mismanagement. Breastfeeding, like sex, is a learned skill, and women need help in communities where the skills have been buried under an avalanche of bottle feeding. The uncontrolled experiment of infant formula feeding since the late 19th century has been an unmitigated disaster. Formula feeding can save lives in some situations, but it still results in many more deaths than it prevents. The 21st century will see class actions by parents of preterm and sick infants damaged by formula (rather than human milk) in many NICUs. Once this begins, societal support and enabling of breastfeeding by mothers and surrogates, along with donor milk banking, will become the norm, and that most processed of all processed foods, infant formula, will be seen as the second rate alternative it really is.
The fact that fathers or friends or grandparents or siblings can bottle feed does not mean that this is natural or even a good idea. But if others do want to feed, breastmilk can be fed by bottle and is preferable to heat-damaged cows milk mixed with multiple synthetic ingredients from multiple nations (including oils made by GM fungi and algae) and inevitably carrying damaging metabolites (check out AGEs, advanced glycation end products.)"