Perspective

Our relationship with the living world is constantly changing. Human population growth and technology alter ecosystems, and other organisms of the Earth adapt as best they can. Some pathogens, such as those that cause smallpox and typhus, fade into the background, whereas others come forward. Examples of the latter are the human immunodeficiency virus and community-associated MRSA. Some changes we can easily understand: a vaccination program eradicated smallpox, and good hygiene plus delousing with DDT knocked typhus out of the headlines. Origins are sometimes unclear, as with CA-MRSA. As we expose bacteria in our bodies and in our surroundings to massive amounts of antibiotics, we strongly favor the growth of microbes with resistance gene....