Biologists studying small children are finding that they naturally have a desire to help others. The children, aged 12-18 months, are quick to help an adult find something they have misplaced or dropped. This behavior changes by the time they reach three years of age--the same time at which they begin to grasp the concept of social norms. Rather than showing everyone equal treatment, they will treat those who have been nice to them in the past better than those who haven't. By this age they have experienced enough interactions in their lives to develop ideas of the correct way to act.
In the end, it seems to come down to a battle between the in-built altruistic nature and the in-built selfish nature of humans. Cooperating in humans goes back to hunter-gatherer societies; a group working together can gather more food than a single man working alone. The necessity to communicate and work together to find food served as a basis of human nature, introducing cooperation and language into society. We have been conditioned to help, because we need it to survive
Image: "fantos fastens" by Brightroyalty on Flickr courtesy of Creative Commons LicensingTweet