We are - according to the neuro-scientist Jonathan Haidt. He sees altruism - acting for others rather than out of self-interest - as an evolutionary development. Even a very young child will come to you aid if you are struggling to open a door, which suggests that this trait is at least partially heritable. Co-operation gives humans a comptetitive advantage over other species - it's our giraffe's neck!
More fascinating insights into some new ideas in psychology here: http://www.nytimes.com/2011/05/17/opinion/17brooks.html?ref=davidbrooks
The Happiness Hypothesis: Finding Modern Truth in Ancient Wisdom by Jonathan Haidt
The Social Animal: The Hidden Sources of Love, Character, and Achievement