Our instincts for fairness and obligations in the social contract evolved when we were organized into tribes. Thus, when we see members of our own tribe (i.e.,

Our instincts for fairness and obligations in the social contract evolved when we were organized into tribes. Thus, when we see members of our own tribe (i.e., those whose children are educated with our own) we instinctively feel drawn to contribute to their well-being. The same thing doesn't work for people outside our tribe. Evolutionarily speaking, these were rivals for our food or mates or whatever. So we don't feel the same compulsion to help outsiders. Here's a counter-example for you: I know several people (and I'm guessing that most of us do) that have exaggerated disability claims, so they're now "retired" and living off social security, when their disability isn't great enough to, e.g., run the machinery to dig a new septic tank. How many people do not try to minimize their tax burden? Isn't that another example demonstrating that people don't naturally contribute to the well-being of those outside their tribes?