Even in a very rational, non-idealistic approach, it's clear that there is a very good argument that altruism is essential to our survival and evolution favoured its development:

Sober argues that, even if we accept an evolutionary approach to human behaviour, there is no particular reason to think that evolution would have made humans into egoists rather than psychological altruists. On the contrary, it is quite possible that natural selection would have favoured humans who genuinely do care about helping others, i.e. who are capable of `real' or psychological altruism. Suppose there is an evolutionary advantage associated with taking good care of one's children -- a quite plausible idea. Then, parents who really do care about their childrens' welfare, i.e. who are `real' altruists, will have a higher inclusive fitness, hence spread more of their genes, than parents who only pretend to care, or who do not care. Therefore, evolution may well lead `real' or psychological altruism to evolve. Contrary to what is often thought, an evolutionary approach to human behaviour does not imply that humans are likely to be motivated by self-interest alone. One strategy by which `selfish genes' may increase their future representation is by causing humans to be non-selfish, in the psychological sense.

http://plato.stanford.edu/entries/altruism-biological/

See also:

DECEMBER 26, 2005

VOICES OF INNOVATION

Nobel Winner Yunus: Microcredit Missionary
Economics professor Muhammad Yunus wasn't afraid to turn the rules of banking upside down

Editor's Note: Bangladesh's Muhammad Yunus and the bank he founded, Grameen Bank, which created a new category of banking by granting millions of small loans to poor people with no collateral--helping to establish the microcredit movement across the developing world--won the Nobel Peace Prize on Friday. On its Web site, the Norwegian Nobel Committee said it awarded the prize to Yunus, 65, and the bank "for their efforts to create economic and social benefit from below."