Lullabies and music to help soothe babies are used by many different cultures around the world - and they may have evolutionary roots. Infant-directed songs may have evolved as a way for parents to signal to children that their needs are being met - while still giving parents enough time for other tasks like obtaining food or caring for other children. These infant-directed songs may then have evolved into the more complex forms of music we hear today. Singing gives parents many opportunities to indicate that they're giving their children attention - such as adjusting their singing, altering their melody and rhythm and adding hand motions, bouncing and facial expressions Researchers aren't sure why music appears in so many cultures around the world, especially because it has no known connection to reproductive success. But a new research paper co-authored by doctoral student Samuel Mehr and Assistant Professor of Psychology Max Krasnow of Harvard University proposes that parents and babies are engaged in an'arms race' battle over their parents' attention.