Here's some new ammunition for the mommy wars: the largest study ever done on the subject of breastfeeding and intelligence has found a correlation between "prolonged and exclusive" breastfeeding and smarter babies. The study, authored by Michael Kramer from the Montreal Children's Hospital, started by identifying about 17,000 Belarusian mothers with newborns. Half of the mothers were given a UNICEF/World Health Organization course—which advised long and continuous breastfeeding—while the other half were left alone to breastfeed at whim. The research team then tracked down about 14,000 of the children six and a half years later to give them IQ tests and examine their school evaluations in reading, writing and math. Sure enough, the babies that were breastfed longer and more continuously scored 7.5 points higher on verbal intelligence than their less-breastfed peers, 2.9 points higher on non-verbal intelligence, and 5.9 points higher on tests for overall smarts—a relatively modest difference, but still significant. This study is the latest in the long string of pro-breastfeeding research linking it to everything from decreasing a mother's risk of developing rheumatoid arthritis to lowering the child's chances of cardiovascular disease later in life. It's also the most recent in the tidal wave of studies linking breastfeeding to higher intelligence—many of which were found to have methodological flaws. While this study appears to be the most conclusive evidence so far of a breastfeeding-IQ link—a fact emphasized by the slew of headlines proclaiming that breastfeeding is the key to baby Einsteins—its conclusions still leaves open the question of why. Is the IQ increase explained by a biochemical response linked to breast milk itself? Or could it be, as Kramer suggests, "something related to the physical contact or the emotional contact between the mother and the baby"? Prior studies point to the former—though as with most things, it may all be in the genes.