pMother#39;s milk may be the first food, but it is not created equal. In humans and other mammals, researchers have found that milk composition changes depending on the infant#39;s gender and on whether conditions are good or bad. Understanding those differences can give scientists insights into human evolution./p a href=http://www.scientificamerican.com/article.cfm?id=boys-and-girls-may-get-different-breast-milk[More]/a