What is an example of altruistic behavior?

Someone who is unselfishly concerned for the welfare of others exibits altruistic behavior. Some examples are:

• Someone who stops at an accident in order to help the victims, even though she will be late to a meeting.
• A student giving someone who does not have money for lunch half of his lunch, even though he is very hungry that day.
• A parent buying a child a new pair of shoes to wear to a dance, even though the parent's shoes are very worn.
• Sterile bees working for a queen.