Why is it that we feel any need to do something for someone else? It is a unique feature of humanity in that nowhere else from the animal world would such a characteristic be found. Animals will do what they have to in order for them to survive, live as a group and to attract a mate. There is no evidence of altruistic behaviour yet in the human world, we find it is quite common.
Human nature is a complex phenomenon to explore that will continue to consume many lifetimes of study. Part of this nature is an inborn need to project ourselves to the world in a manner that we would like to be seen. There are of course exceptions however for the purpose of exploring the nature of doing good deeds, we can exclude those that fall outside any generalisation that follows.
An act based on true altruistic desire is rare because the most noble of good deeds are usually for a specific purpose. This purpose can be as simple as to make the benefactor feel good about himself or herself, or as subtle as expecting something unspecified in return at some time in the future. Good deeds are more often than not the foundation of a harmonious relationship between two or more people, or even between nations. In communal existence, it is therefore a function of survival that we ensure the maintenance of good relationships internally, and with external groups.
Another aspect of good deeds is the fact that we feel a need to nurture those perceived as incapable or weak. In the animal kingdom a weakness is usually considered a liability to the survival of a group and the weak are either killed or left to distract predators from killing the more useful members of a herd. Humans generally protect those unable to fend for themselves and will often do so without any expectation of reward other than perhaps expressions of love.
Groups and organizations founded on values and altruistic systems of belief often train young and old to develop themselves through service to others. Scouting is a worldwide group that promote good deeds', as do Rotary and Lions clubs. The Red Cross along with its international equivalents are renowned for looking out for those in terrible danger, in prisons or in war zones, sometimes at the risk of extreme peril for those attempting to help.
Good deeds come in many guises, and serve an endless variety of purposes however the fact remains that it is only really human nature that sets us above other life on this planet. We are the only ones that have the ability to do good deeds' without necessarily having a good reason.