It's in man's nature to watch out for himself before anyone else but greed (a selfish or excessive desire for more than is needed or deserved, especially of money, wealth, food, or other possessions) is not part of the human nature. Greed and selfishness are traits that are developed over time.
For most people, greed develops as a result of fear of loss or as a result of pain suffered when they were a lot younger. Freed becomes a survival technique for these people. Some people are just greedy by nature, the good thing about this is that, character can be learn and unlearn. A greedy person can work on himself or herself to become generous.
Greed has a firm biological basis, and it has an even stronger social base. The definition of greed is extreme or excessive desire for resources, especially for property such as money, real estate or other symbols of wealth. A person who is dominated by greed will often ignore the harm their actions can cause others.
The customs and cultures we create have a significant effect on the outcome of our behavior, and it modifies our biological reactions. Sometimes the roots of greed in people lie in the lack of understanding among them about the importance of sharing resources and sharing them equitably. Some people do not possess the kind of morality that is necessary to care about others.