Haplodiploid sex determination operates within the hymenopterans, eusocial insect species used as living proof of Hamilton's theory of kin selection as an explanation for the origin of altruism. But there are other eusocial species where this is not a factor, most notably termites and mole rats. Why should these animals be apparently altruistic as well? I can only conclude that haplodiploid sex determination is an incomplete explanation for eusocial kin selection and altruism. It is hard to explain what a soldier termite gets from suicidal altruism, autothysis - it can only be that this self sacrificing behavior benefits kin selection all the same. There are less extreme examples of cooperation, such as cooperative breeding - "if we work together, more offspring will survive to reproduce". The Handicap principle is another explanation for altruism - "I can afford to be impressively wasteful with my resources, therefore I have better genes than most". The Handicap principle is altruism as a demonstration of fitness, a signal, and not entirely for its own sake as it is with the soldier termite whose altruism is not a signal, or means to an end, but an end in itself! "I die that the colony may live." I think that any animal capable of using altruism as a signal can also use altruism for its own sake, but not vice versa, as signals require a certain level of cognitive ability to decode that not all animals possess.
Let's tackle this from another angle and change our perspective - consider the situation from the level of individual cells. A multicellular organism such as a human is composed of billions of cells that are "born" and die, most of which are non-reproductive. So we may easily consider eusocial species to operate as a super-organism, as the single organism and the single insect colony are largely similar. Kin selection operates within my body just as it does clearly in the insect colony. If an animal cannot physically reproduce, how is it any different from a non-reproductive cell within my body? Each, colony and human, operates as the basic unit of sexual reproduction. E.O. Wilson earlier made this same comparison. Are my body cells therefore altruistic, just like the soldier termite? I think so. This analogy allows me to make the following proposition: altruism as an end in itself is something that primarily occurs within the basic unit of sexual reproduction, whereas altruism as a means to another end (as a signal, or handicap) primarily occurs between units of sexual reproduction. Although some have suggested that humans are eusocial, that society forms a super-organism, we are no where near the borg-like eusocial insects, the hymenopterans and termites. Our altruism is at least as well explained by the handicap principle as it is by kin selection. (Besides, if you're helping someone closely related, is it really altruism?) But more to the point I think kin selection and the handicap principle are capable of operating in parallel due to the different processes they affect. Kin selection is natural selection, whereas the handicap principle, so far as altruism is concerned, is sexual selection (a special case of natural selection).