Abundance and absence: Human-microbial co-evolution in the Anthropocene

Human-microbe relations have undergone a profound shift over the past 100 years. The discovery of antibiotics, increasing levels of pollution, and urban and agricultural intensification have led to the proliferation and diversification of novel resistance genes and microorganisms. This abundance has unfolded against a backdrop of microbial absence that is the other side of the antimicrobial coin; reductions in the quantity and diversity of human-microbe interactions are now registering as epidemics of chronic non-communicable diseases in urban populations. Building from this paradoxical situation of 'abundance' and 'absence', this article reviews the molecular-genetic, macroscale-infrastructural, and community-ecological aspects of microbial evolution at a time when human actions are a critical force in shaping their directions.