The origin and erratic global spread of tuberculosis. How the past explains the present and is the key to the future.

Although tuberculosis is a disease known in antiquity, it was not distributed equally or simultaneously throughout the world. Recent genetic studies of the various species of mycobacteria give strong evidence of evolution of M. tuberculosis from saprophytic soil bacteria to M. bovis, which attacks a wide spectrum of lower animals, and then to M. tuberculosis, with the pathogenicity largely limited to humans. The great discrepancies in the time of arrival of this organism to diverse parts of the world, and in its ability to kill the young, account for significant differences in the emergence of innate resistance to tuberculosis in various populations. Innate resistance to particular infections are highly specific, and are derived from whatever scourge one's ancestors had to survive.