Bacteria often provide vivid examples of
how powerful the forces of evolution can be.  In keeping with that,
Hershberg, et al., in a paper published in PLoS, show that evolutionary forces may increase the number of drug-resistent strains of Mycobacterium Tuberculosis (MTB).

They attribute the increase of these strains to both human
demographic conditions (global travel, urbanization, population growth)
and genetic drift.

This is a case when the intersection of evolution and of economics
can have an unsavory effect.  Every 15 seconds a person dies of MTB.

Furthermore, we found that the global
diversity in tuberculosis strains can be linked to the ancient human
migrations out of Africa, as well as to more recent movements that
followed the increases of human populations in Europe, India, and China
during the past few hundred years. Taken together, our findings suggest
that the evolutionary characteristics of tuberculosis bacteria could
synergize with the effects of increasing globalization and human travel
to enhance the global spread of drug-resistant tuberculosis.

References

High Functional Diversity in Mycobacterium tuberculosis Driven by Genetic Drift and Human Demography Hershberg R, Lipatov M, Small PM, Sheffer H, Niemann S, et al. PLoS Biology Vol. 6, No. 12, e311 doi:10.1371/journal.pbio.0060311