A group of researchers report in PLoS Biology that Mycobacterium tuberculosis strains that affect people are more genetically diverse than had been assumed. They studied 7 megabase pairs of DNA sequence data from 108 strains of M. tuberculosis and attribute the diversity to human demographic and migratory events. The authors also say that current human population trends, global travel, urbanization, and population growth, may be contributing to the spread of drug-resistant tuberculosis