Evolutionary theory would be compatible with altruism if we could expect the same in return. One monkey picks the parasites from the back of his monkey friend, then his monkey friend returns the favor. But it is hard to see how the 'you scratch my back, I'll scratch yours' gene could ever gain dominance in the first place.
Across many universities beside York, from St. Andrews to Chester, university Christian Unions are known for their regular acts of goodwill and their members' enthusiasm. 'Grilling a Christian' is not the first time that the University of York's Christian Union has hosted an atypical event on campus and it won't be the last.