In light of the world's outpouring of aid, Philosophy etc considers the old problem of altruism. But as Sock Thief points out, from an evolutionary perspective, there is no such thing as altruism, only a higher form of selfishness. Biologists examining the problem quickly realised that altruistic organisms would be less fit than selfish ones which invested all their resources in themselves rather than sharing with others. But at the same time, "altruistic" behaviour was widespread in nature, ranging from food-sharing in numerous species of animal, the complex social structures of the social insects, and wealthy humans assisting both members of their own communities and others in far-off countries struck by natural disasters. How can this be explained?
One explanation revolves around the genes and the concept of inclusive fitness. One gene is more "fit" than another if more copies of it are present in the next generation. The conceptual breakthrough behind inclusive fitness was realising that those copies need not be present solely in the genomes of direct descendants, but could be anywhere; all copies are equal as far as the genes are concerned. The fitness of an individual organism therefore depends not just on the survival of its descendants, but also on the survival of its close relatives and their descendants, who are statistically likely to share its genes. This leads directly to the idea of kin selection - that organisms will help their relatives because doing so is (to some extent) helping themselves.
These two ideas have been remarkably powerful in explaining animal behaviour, particularly that of the social insects (and their creepy mammalian mimics, the naked mole rats). But they're by no means the whole story; animals do not limit altruistic behaviour to their close relatives, but help non-relatives as well. Here biologists fall back on game theory. It's intuitively obvious that a strategy of undiscriminating altruism will be beaten by a strategy of exploitation or cheating (accepting help and giving none in return). But once you add discrimination into the mix, then everything changes. In particular, a strategy of discriminating strongly against people who have cheated you in the past - holding grudges, in other words - can outcompete both (it is what is known by biologists as an Evolutionarily Stable Strategy, or "ESS"). And once you add communication, allowing individuals to share information about who the cheats are<, the balance tips even further. This explains the leftover altruism in higher animals (those capable of distinguishing different individuals and tracking past behaviour).
So according to biologists, we're not really altruistic. All that money is being contributed not because we genuinely care for the victims of the tsunami, but because we expect them to one day pay us back.
Does this leave any space for altruism? Yes. The important thing to remember is that we are not our genes. Instead, we are "survival machines" built by them to assist in their replication. And most importantly, we are survival machines with minds of our own. Yes, those minds are shaped by our genes - but beyond establishing some broad personality traits and default desires to guide us in the right direction, we are on our own. Those broad personality traits include some designed to promote kin selection and reciprocation - concern for close relatives, sympathy for those in need, and anger at those who cheat us - but they certainly don't dictate, and they certainly don't rule out altruistic behaviour. Our genes may be selfish, but we don't have to be.