What are some acts of altruism you have experienced or heard about?

Personally, I don't think I have ever heard of experienced true altruism. Can something really be done without the person wanting anything in return? Yes. I think of Mother Theresa, but have only heard about what she did. I have no personal experiences with altruism. Does it happen often? I'm not sure about that. I once paid for someone's purchase at Wal Mart. They had just moved here and her debit card wasn't working, they didn't have cash, and she had her little girl with her. I wasn't trying to eavesdrop but I could tell she was on the verge of tears and trying to explain to the woman on the phone who was with the credit card company that they had to buy whatever it was they were buying. The purchase was close to $200 and we don't really have a lot of money but I told the cashier to put her purchase with mine, which was only around $12. I paid for it and walked out and just told the lady it was taken care of. I didn't want recognition so I walked out quickly. I would like to think I did that altruistically but I did feel good when I did it. Maybe I did it because I felt good helping someone. I'm not sure, but I believe someone can do something altruistic.