Infection

Most microorganisms are harmless to humans: indeed, our very own eukaryotic cell can be understood to be several different kinds of microorganisms that evolved into a single physical entity several billion years ago. Thus we are a collection of microorganisms that we attempt to control and modify with our genes. Beyond this however, the external surfaces of our bodies are extensively colonized by bacteria, many of which can be seen to be absolutely key to the maintenance of life.