Mr. Nice Guy gave a good example in another thread in where you have two infants playing with the same toy. You give one infant a bigger, shinier toy, and the other infant now wants that very same toy. Why is the infant without the bigger toy satisfied with what it has? Why does he now want that bigger, shinier toy? These are infants that have gained LITTLE external experience and are mostly driven on innate traits at this point.
Props for remembering that, because I had forgotten about it lol.
I know you do some charity stuff, right? Does it make you feel good that you help out? If so, then you are still doing that for self, as well as helping others out. As I said, EVERYTHING we do is to either gain pleasure or avoid pain...it is the basic rule of motivation and incentive. EVERYTHING we do has motivation behind it, and every motivation is followed by an incentive. Therefore, every action we take is to gain incentive.
Another good reason why humans tend to do good things for others or essentially practice altruism is that our brains have not had time to evolve out of the tribal, small community mentality. In other words, we have lived in large, connected societies for such a short time relative to our otherwise that our brains have not yet evolved to change our characteristics to maximize our survival and reproduction in these circumstances.
In the same way that we have an inherent fear of snakes but not of cars even though cars kill many more people a year then snakes, our brains have not evolved at the same pace as our societies, leaving us with characteristics and impulses best suited for life in a small, hunter/gather or possibly nomadic community.
Therefore, our brains tells us to be altruistic because while you may help someone and never see them again in a big city, in a small community, you can expect your favor to be remembered and returned; and our brains still live in that small community.
This is the same thing many sociologists look to when analyzing humans interest and sometimes over the top emotional attachment to sports teams. In our mind we identify with those teams like we were part of the same tribe, and sports plays off our evolved characteristic to fight for our tribe and dislike other tribes, which explains why people will sometimes fight and kill over something as irrelevant and arbitrary as watching other humans compete in some athletic activity.