Sampling the mobile gene pool: Innovation via horizontal gene transfer in bacteria

In biological systems, evolutionary innovations can spread not only fromparent to offspring (i.e. vertical transmission), but also ‘horizontally’ between individuals, who may or may not be related. Nowhere is this more apparent than in bacteria, where novel ecological traits can spread rapidly within and between species through horizontal gene transfer (HGT). This important evolutionary process is predominantly a by-product of the infectious spread ofmobile genetic elements (MGEs). We will discuss the ecological conditions that favour the spread of traits by HGT, the evolutionary and social consequences of sharing traits, andhowHGTis shaped by inherent conflicts between bacteria andMGEs. This article is part of the themed issue ‘Process and pattern in innovations from cells to societies’.