Altruism happens usually among members of a tightly knit group, like family members or soldiers of a given unit. Teachers sacrificinng their life to save children. FOSS-developers, are they really producing software out of altruism? Maybe some of them are but it is hard for us to know whether that is so or not.
But the truth is - so do I - as a humble contributor to a document, test, bug fix, or feature add to a FOSS project - where's the beef?
Totally altruistic!