When our ancestors set off from the cradle of civilization on their journey toward populating the planet forty-thousand years ago, tuberculosis hitched a ride with us and has been with us ever since. Mycobacterium tuberculosis, the organism responsible for TB, has learned through natural selection to be an almost perfect pathogen. The bacterium can enter into a latent state when a host's immune system is strong, only to come back to life when the immune system has become weakened. TB even has come up with clever ways to avoid being killed by antibiotics. Throw in the compounding problems...