Researchers at Durham University have found that the longer a child is breastfed, the bigger the size of their brain, and that there is a direct correlation between the size of a mammal's brain and the amount of time they suckle. The scientists were not sure whether it was the energy that milk supplied or the nutrients that made the difference. The team studied 128 mammal species, including humans. They found that the length of the gestation and suckling periods affected the size of the brain. The study was published in Proceedings of the National Academy of Sciences. -- Daily Telegraph, March 29, 2011