There's an article in this month's Scientific American about drug-resistant bacteria that help their more vulnerable counterparts survive onslaughts from antibiotics. The resistant bacteria secrete a molecule called indole which helps the non-resistant bacteria by activating drug-exporting pumps on their cell membranes. The catch is that secreting indole weakens the resistant bacteria, adversely affecting their own growth.
Obviously this is nothing like altruism in the sense we talk about it in humans or other primates. Our own altruistic behavior is driven by a deeply embedded biological tendency toward empathy, stirred together with a vast array of ever-shifting sociocultural ideologies. Bacteria, lacking brains, aren't capable of feeling empathy and certainly not of developing sociocultural norms.
But there is a lesson here that I think is worth shoving in the face of creationists, and that includes "theistic evolutionists" who believe our moral intuitions are derived from a divine being: that contrary to the popular misconception, nature is not "dog eat dog". Populations of species, even on the microscopic level, survive and thrive through cooperation, and self-sacrifice for the greater good is by no means a uniquely human phenomenon – it's something we can observe at a fundamental biological level across an astonishing spectrum of species.