Evolutionary Theory in action. Babies cry to prevent parents from procreating. It is a survival strategy for maximizing resources without the interference of those pesky infant siblings that sap up the bulk of resources such as attention and investment of time. Keep parents occupied and no brothers or sisters 🙂    Read about it here:

http://www.independent.co.uk/life-style/health-and-families/health-news/babies-cry-at-night-to-stop-mothers-procreating-scientists-claim-9265668.html