Abstract: When do we care for others as we care for ourselves? William Hamilton showed that we should be expected to care for our family members in proportion to our degree of relationship to them. Such reasoning explains why eusociality evolved independently at least twelve times in the order Hymenoptera, which includes ants, bees, and wasps, but only three times elsewhere in the animal kingdom. It also verifies Thomas Hobbes' answer to the question: Why cannot mankind live sociably one with another as bees or ants?

Keywords: sympathy, empathy, degree of relationship, kin selection, Hamilton's rule, social insects, eusociality,