All biological processes are under some type of logical regulatory control.  In the immune system, cells called Macrophages eat dead and worn out cells and bacteria.  If this process was not controlled we would eat ourselves up from the inside.  Worn out cells which need to be recycled have on their surface a protein euphemistically called the "eat me" signal.  And, as you might expect, there is also a "don't eat me" signal protein.  Cancer cells are able to evade detection by the immune system, sometimes by displaying the "don't eat me" signal on their surface and are thus not attacked by macrophages.  Blocking this signal with another protein can allow one's immune system to recognize and attack cancer cells.  But where did the logic behind the design of this regulatory mechanism come from?  Uplook Magazine, April 2013, p.24.  References:  http://med.stanford.edu/ism/2010/december/crt-signal.html;  http://www.genengnews.com/gen-news-high-lights/blocking-don-t-eat-me-signal-on-cancer-cells-lets-phagocytes-clean-up/81246548/