High Functional Diversity in Mycobacterium tuberculosis Driven by Genetic Drift and Human Demography
(A) Global human population size during the last 50,000 y. The letters above the graph indicate the time periods corresponding to (B), (C), and (D), respectively (data source: http://en.wikipedia.org/wiki/Image:Population_curve.svg). (B) Hypothesized migration out of Africa of ancient lineages of MTBC. Colored arrows correspond to the six main human-adapted MTBC lineages shown in Figure 1. The hypothesized common ancestor of the three modern lineages (in red, purple, and blue) is indicated in black.
(C) Recent increase of global human population. Each dark grey dot corresponds to 1 million people (data source: http://www.pbs.org/wgbh/nova/worldbalance/numb-nf.html). The population increase was strongest in Western Europe, India, and East Asia (Figure S3). These three geographic regions are each associated with one of the three modern MTBC lineages (red, purple, and blue). Recent human migration, trade, and conquest have promoted global spread of these modern MTBC lineages.
(D) The human population has reached 6 billion. The distribution of the six main human-adapted MTBC lineages we observe today is shown (colors correspond to Figures 1 and S2; based on data from [19,21]).