Where do genes come from? Traditionally, most models for new gene evolution invoke modifications of ancestral genes.
The human microbiome (microbial communities and their gene content) is composed of trillions of cells in multiple ecological niches. Although the lung was initially believed to be sterile in the normal host, recent data indicate that microbial communities are detectable in individuals without lung disease.
Bacterial pathogens have evolved a plethora of different adaptations that confer high-level resistance to certain antibiotics. However, it remains unclear whether the observed adaptations are randomly drawn from a much larger set of possibilities or represent the best of only a few options for obtaining resistance.