Q. Most biologists believe that the immune system's defence against infections largely rests on its capability to distinguish self molecules from non-self molecules. This concept seems central to our understanding of immune function. Yet, like all scientific ideas, it is not beyond question. Several immunologists have developed an alternative hypothesis: that the immune system's effectiveness rests mostly on its ability to recognize damage to body tissues caused by the invaders, not on the ability to recognize non-self. If you were going to test the "damage" hypothesis, what might you look for? Which form of cell would you expect to be directly affected by damaged tissues and why? Some proponents argue that the "damage" hypothesis makes more sense from an evolutionary perspective, claiming that it is more advantageous for an organism's defence system to respond to tissue damage than to the mere presence of a foreign microbe. Do you be in agreement? Why or why not?