The Virus That Learns

If you don’t have an immune system, you don’t last long in this parasite-riddled world. Your body receives a steady stream of invaders–viruses, bacteria, and other pathogens–which it has to recognize and fight. In many cases, it’s a brutal battle with an ultimate goal of eradication.

http://phenomena.nationalgeographic.com/2013/02/27/the-virus-that-learns/